Election of Tone Control Parameters-See Page MAR(H 1953

Selection of Tone Control Parameters-See Page MAR(H 1953

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here are the 30 BEST SELLING RECORDS OF 1952*

... and over 43% used adiotapr' for the original sound!

Like Audiodiscs and Audiotape, this record speaks Made from Audiodisc for itself. Record, Artist S Label Master Of the thirty top hit records of the year, all but BLUE TANGO (Leroy Anderson- Deeea) WHEEL OF FORTUNE (Kay Starr-Capitol) Y. one were made from Audiodisc masters! And that CRY (Johnnie R y -Okeh) Y. one - a London Record - was made abroad. YOU BELONG TO ME (Jo Stafford -Columbia) AUF WIEDERSEH'N, SWEETHEART (Vera Lynn -London) It is significant, too, that the original recordings I WENT TO YOUR WEDDING (Patti Page- Mercury) HALF AS MUCH ( Rosemary Clooney- Columbia) for over 43 per cent of these records were first made WISH YOU WERE HERE (Eddie Fisher - DugO II'in tech alter- Victor) on Audiotape, then transferred to the master discs. HERE IN MY HEART (.41 Martino -BBS) This marks a growing trend toward the use of DELICADO (Percy Faith -Columbia) Audiotape for the original sound in the manufac- KISS OF FIRE (Georgia Gibbs - Mercury) ANY TIME (Eddie Fisher -Hugo Wiaterhalter- Victor) ture of fine phonograph records. TELL ME WHY (Four Aces -Decca) BLACKSMITH BLUES (Ella Mae Morse- Capitol) Yes - Audiodiscs and Audiotape are truly a IAMBALAYA (Jo Stafford- Columbia) record- making BOTCHAME (Rosemary Clooney- Columbia) combination -in a field where there GUY IS A GUY (Doris Day -Columbia) can be no compromise with Quality! LITTLE WHITE CLOUD THAT CRIED (Johnnie Ray- Okeh1 Trade Mark HIGH NOON (F'rankie Laine- Columbia) t I'M YOURS (Eddie Fisher -Hugo Winterhalter- Victor) GLOW WORM (.Mille Brothers -Decca) IT'S IN THE BOOK (Johnny Standley- Capitol) SLOW POKE (Pre ITS' Ki,ny- Victor) WALKIN' MY BABY BACK HOME (Johnnie Ray -Columbia) MEET MR. CALLAGHAN (Les l'aul- Capitol) I'M YOURS (Don Cornell- Coral) I'LL WALK ALONE (Don Cornea - Coral) TELL ME WHY (Eddie Fisher-Hugo Winterhalter- Victor) TRYING (llilltoppers -Dot) PLEASE, MR. SUN (Johnnie Ray - Columbia) AUDIO DEVICES, INC.

l r turning to Retail Sales, as listed in THE BILLBOARD. 444 MADISON AVE., NEW YORK 22, N. Y Export Dept.: 11 East 40th St., New York 14, N. Y., Cables "ARLAS's

Audiodiscs are manufactured in the U.S.A. under esderiys license from PYRAL, S.A.R.L., Parir

www.americanradiohistory.com Successor to 1917 1 ,7c7 -Established AUDIO INCLUDING > PHYSICISTS EPVGIIIEERING; AND ENGINEERS C. G. McProud, Editor and Publisher Harrie K. Richardson, Associate Editor Ec gar M. Villchur, Contributing Editor ATTENDING THE Eve Drolet, Product on Manager Henry A. Schober, Business Manager Edgar E. Newman, Circulation Promotion S. L. Cahn, Advertising Director Elizabeth Beebee, C rculation Manager H. N. Reizes, Advertising Manager

Editorial Advisory Bcard Representatives CONVENTION H. Thorpe Covington Special Representative NEW YORK CITY Howard A. Chinn 677 N. Michigan Ave.. Chicago 11, Ill. z3 lohn D. Calvin Sanford R. Cowan, Mid -West Representative MARCH -26... 67 W. 44th St., New York 18, N. Y. C. I. LeBel

I. P. Maxfield West Coast lames C. Calloway J. W. Harbison Inquiries are George M. Nixon 816 W. 5th St., Los Angeles 17, Calif. invited regarding CONTENTS MARCH, 1953 Vol. 37, No. 3 openings Audio Patents -Richard H. Dorf 2 on our Staff Letters 8

Employment Register 10 RADAR LABORATORIES New Literature 12 GUIDED MISSILE LABORATORIES Audio Photographer's Checklist -Eugene F. Coricil 14 ADVANCED ELECTRONIC LABORATORIES Effect of Load Impedance on Magnetic Pickup Response -Norman Pickering 19 ELECTRON TUBE LABORATORIES A Power Tubé Figure of Merit -Warren G. Bender 21 FIELD ENGINEERING DEPARTMENT The Selection of Tone -Control Parameters -Edgar M. l'illchur 22 Audio in the Year 1693 -Allen H. Fry 25 For the convenience of Auxiliary or Emergency Broadcast Control Room- Harold Reed 26 > those attending the I. R.E. The Columbia "360"-Peter C. Goldmark 28 meetings and Radio Engineering Theater in Sound A Small Package -Part 2- Thomas R. Hughes 30 Show, members of the Handbook of Sound Reproduction-Chapter 10 -Edgar M. I'illehur 32 Laboratory Ste will be available 1953 Radio Engineering Show 38 for interviews at the First Inventor Under the 1952 Patent Law- Albert If'oodruff Gray 40 Convention hotel. For appointment telephone Hughes New York Audio Fair -Los Angeles Rated Huge Success 42 office, LAckawanna 4 -935o. Equipment Report- Pilottnler and Pilotone Amplifier 44 Record Revue- Er:yard Taman Canby 46 New Products 54 Errata 55 Industry People 71 Advertising Index 72 HUGHES COVER Recording voice on previously made film by means of magnetic sound track is becoming increasingly important in radio and TV. Reeves Soundcraft's Magnestripe process is being demonstrated RESEARCH AND by Georgia Landeau, DEVELOPMENT LABORATORIES NBC -TV featured actress. At the left is shown the RCA Model 400 projector which reproduces both optical and magnetic Scientific and sound tracks, and which incorporates a recording Engineering Staff amplifier for use with the Magnestripe process. CULVER CITY, LOS ANGELES COUNTY, CALIFORNIA RADIO MAGAZINES, INC., P. 0. BOX 629, MINEOLA, N. Y. Assurance is reàuired that relocation AUDIO ENGINEERING (title registered of the applicant will not cause disruption II. S. Pat. OIT.) is published monthly at 10 McGovern Avenue, Lancaster, Pa. by Radio Magazines. Henry Inc.. A. Schober, President; C. B. McProud, Secretary. Executive and Editorial Offices: of an urgent military project. 204 Front St., Mineola. N. Y. Subscription rates -United States, U. S. Possessions and Canada. $3.00 for 1 year, $5.00 for 2 years; elsewhere $9.00 per year. Single copies 35c. Printed in U. S. A. All rights reserved. Entire contents copyright 1953 by Radio Magazines, Inc. Entered as Second Class Matter Februay 9, 1950. at the Post Once. Lan- caster, Pa. under the Act of March 3, 1879

AUDIO ENGINEERING MARCH, 1953 1

www.americanradiohistory.com ISS umitez RICHARD H. DORF

I SEEMS that it is time once again to really good thinking and problem repeat a definition given a long time ago solving. This column is a review rather ::f the purpose of these monthly patent than a normal article, selecting as many articles. The thought arises because among interesting (to the writer, anyway) patents your letters sometimes appears one pointing as space allows and turning the abstruse out that for this and that technical reason patent -specification language into technical SONOCRAFT one of the patents described here is not English. We make every effort to either all it is cracked up to be, as far as per- reject or plainly label patent ideas that are FM TUNER formance is concerned. truly unworkable, but -paraphrasing the Now, don't get me wrong : such letters common radio parlance-the opinions ex- America's Most Advanced Tuner are as welcome as other mail. They show pressed are almost entirely those of the knowledge and astuteness on the part of the inventors. COMPARED ... by engineers and writers, and they often give additional While on the subject of mail, here is an critical music - lovers for audio-quality. food for thought. But sometimes they say answer for those who would like circuit and technical advancements. Consen- in effect (often between rather than on the component values in all the schematics. sus of comment: "Amazing tonal qual- lines) that since the deficiency is present Whenever the patent furnishes them, we ity" ... "True fidelity of reproduc- we ought not to describe the patent. And put them there in plain sight. If we haven't tion" ... "Live programs really sound there's the point of disagreement. done so, they aren't available. live!" These articles are different from most And now, on to this month's review. and found con- others. They don't purport to give ab- M sistently e ective for fringe-area re- solutely reliable information right from the Distortion ement ception at distances from 40 to 80 writer's or other engineer's mouth ; they Owen E. DeLange's patent No. 2,618,686 miles from New York City ... New, don't mean to imply that the inventions de- shows a visual method of distortion meas- super- sensitive circuit assures perfect scribed are either good or bad; they don't urement using the outphasing principle. signal pick up with sufficient quieting even indicate that the inventions will The purpose (probably used in wideband for excellent reception even in remote positively work. What they try to do is amplifiers-the patent is assigned to Bell locations. Automatic Frequency Con- present ideas that seem interesting for any Labs) is to check distortion in terms of trol (AFC) prevents station drift. of dozens of reasons -because the approach compression or expansion- nonlinearity- to a problem is new or ingenious (or both), rather than in terms of harmonic produc- . . . because of its because there is an idea that could be de- superior per ormance, its compact tion, though the two are, of course, rigidly veloped further, because the invention shows related. The method is simple, requiring no dimensions for easy mounting into a somewhat different- though not neces- any enclosure, its new type precision equipment, and is shown in block almost sarily better -way of doing a common tuning indicator (simpler to use) and form in Fig. 1. thing, because, although the object of the The principle is to generate a wave of many other exclusive features .. . invention may be unnecessary or impracti- definite form, such as a sawtooth, and feed * * * cal, somebody did put together a weird it through the system under test. The wave SPECIFICATIONS: New black -out tun- brainstorm of a circuit, parts of which is simultaneously fed through a "balancing ing indicator; 3 gang inductive tun- might give someone an idea that would be branch." The waves from the two branches ing; dual limiter; all coils slug -tuned; practical, and so on. are applied to a balancing circuit in which 5 microvolt sensitivity for 20db quiet- To a large extent, the technological his- their levels are equated and the phases are ing; 200 KC bandwidth at 6db down; tory of the United States is represented by made opposite. This produces cancellation adjacent channel down 60db; eleven its patent files. Not many of us are ingeni- provided both waves are the same (no miniature tubes plus neon- tuning in- ous and original enough to solve every distortion in the tested system). If there dicator; AFC with disable switch; design problem right from scratch ; and has been a change in waveform in the test compact size: 10 "w., 4 "h., 8 "d.; new the wealth of ideas present in the flood of branch, the resultant signal out of the bal- design for simplified installation. patents issued monthly (to which most ancing circuit contains the difference be- people don't have access and the time to tween the original and distorted forms, SONOCRAFT FM TUNER $89.95 spend) furnishes many a take -off point for which is shown on an oscilloscope. Write for descriptive bulletin ER which Operation is as follows : Attenuator A is contains a complete equipment report on *255 W. 84th St., New York 24, N. Y. adjusted so that the signal furnished the this tuner.

SYSTEM Gitt: ?y U"OE TEST Come in and pick up or write for your free copy of 4--TEST BRANCH I: "Sound Advice" written --. for Music Lovers, by Irving Greene. 124 pages of vital information in .TOOT" stPe. n TTE"uATO. high fidelity. 4ExfiW

BALANCING BRANCH -. Asco SOUND A CORPORATION C 115 WEST 45th STREET, 3rd FLOOR NEW YORK 36, N. Y. Fig. 1

2 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com 9- 19. a Búl REK»O-KUT

hz -12aig 'I' Record Reproduction begins with the rotating motion of the record! This motion expresses passage of time. And each rotation is an interval or segment of that time. This important function is en- trusted to the turntable.

The faithfulness with wh:ch the turntable, a purely mechanical device, can perform this task, is related entirely to its design and construction. It is pretty generally known that any mechanical vibration will impose itself as undesirable elements of distortion in the reproduced sound, and that speed deviation will result in a variation in time or tempo, and in undulating pitch. There is no compromise with turntable quality if the best in sound reproduction will be had. Engineers know this, and the name of REK-O-KUT is a byword in professional circles as the standard of turntable quality. But whether professional sound engineer or simply a lover of good sound, only a fine turntable can justify the fine equipment of a modern high fidelity system. _ t/ {, .;

Among the seven REK-O -KUT Turntables available are: Model LP743- Induction Motor Three Speeds, 33%, 45 and 78 $ 54.95 Model T -12H- Hysteresis Motor Two Speeds, 331 and 78 119.95 Sold by Leading Distributors Model T-43H- Hysteresis Motor Two Speeds, 33% and 45 119.95 Write for Descriptive Literature

R EK - O -KUT CO. 38 -038 QUEENS BOULEVARD LONG ISLAND CITY 1, NEW YORK

Export Division: 458 Broadway, New York 12, U. S. A. Caales: Morhanex In Canada: Atlas Radio Corp., Ltd., 560 King Street W., Toronto 2B

AUDIO ENGINEERING MARCH, 1953 3

www.americanradiohistory.com Fig. 2. test branch is within the nominal capabili- ties of the tested system. Then the switch in the test branch is opened and attenuator B is adjusted so that the oscilloscope trace has a peak vertical deflection of 10 divisions. Next the switch is closed and attenuator C adjusted so that the two branch outputs are balanced by placing as much as possible of the center of the resultant wave on the zero horizontal axis on the oscilloscope screen. The peak deflection of the resultant wave then shows the amount of difference between the undistorted wave of the balancing branch and the distorted wave of the test branch. Since the original wave was set to 10 divisions peak value, each division for the resultant is equivalent to 10 per cent distortion. If the distortion is less than 10 per cent, the loss of attenuator D may be reduced by 20 db, which gives a factor of 10, making each division equal to 1 per cent distortion. In high- frequency systems or video amplifiers time delay in the tested system may make coincidence of the outphased waves impossible. This can be cured by placing a variable delay line in the balancing branch to make the delays equal. At audio frequencies the delay would be very much smaller than the period of the test waveform, so that delay would not be a problem. The balancing .circuit might be any of Meet the Redheads... several. The inventor shows a simple but quite suitable one, redrawn in Fig. 2. V, is tape recording a phase -inverter stage which allows selec- tops for tion of output from either plate or cathode, the one wanted depending on the output See how the latest additions to the Brush family of magnetic phase from the tested system. The input recording components can improve your tape recorders! potentiometer is equivalent to attenuator C in Fig. 1. The BK -1090 record -reproduce head has the standard track The output of the phase inverter is ap- width designed for dual track recording on /. inch tape. It pro- plied to the cathode of the balancing (really vides unusually high resolution and uniformity over an extended simply a mixing) stage, while the test range. resin construction assures dimensional branch output coming through a potenti- frequency Cast ometer acting as attenuator B, is applied stability, minimizes moisture absorption, and affords freedom from to the grid. The output of the stage can be microphonics. Its balanced magnetic construction, precision fed to an oscilloscope, with the vertical lapped gap, Mu -metal housing, and single -hole mounting provide amplifier gain control acting as attenuator important design advantages. D. The BK -1110 erase head has the same basic construction as the Phase Splitter companion record- reproduce unit. Its outstanding feature is its There are probably more phase -splitter device in efficient erasing at low power consumption -less than I/: voltampere. circuits extant than any other the audio world. Almost all give unbalance Investigate these new "Redheads" for your magnetic recording. problems at the extreme ends of the fre- Your inquiries will receive the attention of capable engineers. Write quency range, which gives rise to response is a circuit Brush Electronics Company, Department ZZ- 3,3405 Perkins Avenue, dropoffs and distortion. Here the inventor claims will remain in perfect Cleveland 14, Ohio. balance between 20 and 150,000 cps. Illus- trated in Fig. 3, it was invented by Louis R. Bourget of Sacramento, Calif., and is the BRUSH ELECTRONICS COMPANY subject of patent No. 2,618,711. formerly uses three triodes (two of RESEARCH INSTRUMENTS The Brush Development Co. The circuit INDUSTRIAL AND IM be, as shown, the halves of a PIEZOELECTRIC MATERIALS ACOUSTIC DEVICES in Brush Electronics Company which may .AIM is as a MAGNETIC RECORDING EQUIPMENT =S. is an operating unit of dual- triode). The first operated (IC(T ROMICS ULTRASONIC EQUIPMENT Clevite Corporation. cathode follower, with R, the volume con-

4 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com Here is the first basic advance in tone arm design in many decades!

The GRAY "Viscous- Damped" 108 -B Tone Arm

Gives you perfe ^t contact and tracking on all records at lowest stylus pressure- virtually eliminates tone arm resonances- cannot damage record if accidentally dropped.

The entirely new suspension principle of The 108 -B satisfies every requirement of the Gray 108 -B makes it hug the grooves .. . high fidelity reproduction. A plug -in feature prevents stylus skidding on worn records - permits instant change from 78 -rpm to 33%. overcomes groove -jumping caused by floor rpm or 45 -rpm, with automatic adjustment to vibrations. Its "viscous-damped" design pro- the correct stylus pressure. See and try this vides perfect tricking, virtually eliminates "viscous- damped" arm soon - solve all your tone arm resonances, and prevents any pos- transcription problems with this revolutionary, sibility of record damage if the arm is dropped. versatile arm! r Cray Research & Development Co., Inc. I Hilliard Street. Manchester, Conn.

Please send me your Bulletin RF -3 on the new Gray "Viscous-Damped" 108.8 Tone Arm. G Rsiat NAME AND DEVELOPMENT CO., INC., HILLIARD STREET, MANCHESTER, CONN. ADDRESS Division of The CRAY MANUFACTURING COMPANY-Originators of the Cray Telephone Pav Station and the Grit, Audograph and PhonAudograph CITY STATE

AUDIO ENGINEERING MARCH, 1953 5

www.americanradiohistory.com 50.000 .3 like it fr°14Tps

ay RAY ANTHONY The Yount' Mon Wh o Hord'

... about the famous new fig. 3. trol and R, the cathode resistor. The secret slender gradient' of the circuit's success is said to be that the actual phase-splitter tubes V, and V, are fed from the same low- impedance source high -fidelity bi- directional and the antiphase outputs are symmetrically obtained from identical plate circuits. V, is fed as a grounded -grid stage by microphones paralleling its cathode with that of V,; the plate output is therefore in the same phase as the circuit input. V, is a conventional grounded -cathode amplifier but the low - impedance source effectively eliminates input capacitance effects. Its output is, of course, out of phase with the circuit input. The output capacitances of both V. and V, should be the same, causing no unbalance such as would be obtained from the "long - tailed" or "split- load" circuits. Miller ef-

"315" General Purpose

LIST PRICE $7 5.00

Fig. 4. fect is probably less in V, than in J/, because there is some cathode degeneration in V,. For high -fidelity, true -tone reproduction of The latter probability is cleared up in the voice and music, these small and rugged microphones are modification of Fig. 4, where the cathode destined to be the favorites of leading recording artists resistor of V, is left unbypassed. Cathode degeneration is then probably about equal singers -instrumentalists bands everywhere. ... -and in both tubes. This reduces the amplification of V,, which is compensated by tapping the These microphones will outperform all other input for V. down on R. and adding the "slender" microphones- because of their 500 -ohm resistor for bias compensation. The circuit of Fig. 4, by the way, is suitable for advanced acoustical, electrical, and mechanical d.c. amplification because of the elimination features. Both models provide a hi- directional of the V, cathode bypass capacitor and the pickup pattern -permitting greater per- output blocking capacitors. This may inter- former freedom (performers can stand at a est instrumentation workers and direct - 73% greater distance from the microphone!) coupling fiends in the audio field. In either should be equal The "300" and will pick voice music circuit, R. adjusted for "315" up and plate currents through V, and V,. In Fig. from front and back -yet discriminate against unwanted 4, the tap on R. may also be touched up a noises from the sides. They reduce reverberation and the little if necessary for equal audio outputs. pickup of distracting random noises by 66%! R, need not be adjustable, of course (the best setting was found to be at 3,000 ohms) but may be useful when tubes get old or are replaced if precise balance is wanted. .cA n.. Poem. Pending Video Beckons a MANUFACTURERS of MICROPHONES I should like to close this chapter with SHURE BROTHERS, suggestion which may provoke some audio Inc. and ACOUSTIC DEVICES engineers and enthusiasts (the terms are 225 West Huron Street, Chicago 10, Illinois Cabre Address: SHUREMICRO (Continued on page 56)

6 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com The Inside Story I

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HERMETICALLY SEALED IN CAST EPDXY. EXCEEDS MIL R -93A SPECIFICATION

Scientific progress has made the demand and we believe the CE series resistors are the answer: - In the cross -section above, we illustrate the single homogenous mass that means so much to stability and provides the ample moisture vapor barrier of this new resistor. Bobbin and encapsulation become one homogenous mass, surrounding the resistance wire with a minimum of strain. Write today if your requirements are for a hermetically sealed resistor to withstand a wide variety of environments. Ask for the literature covering the CE series resistors.

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AUDIO ENGINEERING MARCH, 1953 7

www.americanradiohistory.com here's LETTERS Help Wanted!

SIR : absolute reliability A number of months ago I took up the subject of beats and combination tones with the technical editor of Radio and Hobbies in Australia. We consulted L. L. Beranek's "Acoustic Measure- ments," E. G. Weaver's ''Theory of Hearing," Watson and for heavy duty Tolan's ''Hearing Tests and Hearing Instruments," and Harvey Fletcher's "Speech and Hearing." As yet we have not established where in the auditory system the difference between the two exists. We would appreciate any comments on this subject which audio your readers would care to put forward. JOHN F. MCDERMOTT, Flat 36, 2 Anderson St., amplification Kingsford, N.S.W., Australia. Stereo Photos

SIR : .- It is now a year since you first used stereo photos in the magazine, and I have been waiting for further use. I feel that they are 41471 a very good way of presenting devices that have interesting spatial features. I hope that you are continuing to solicit their r '`91d I'417%o use in future articles where they would be appreciated. ROBERT P. ST. JOHN, 6606 Woodlawn Ave., oltim Chicago 37, III. (We still want stereo photos to illustrate articles if they will submit them, and if they do we will print them. However, it ap- 'tipi pears that few of our authors remember our offer, and we shall have to use this interesting form of photography to illustrate our r own articles in the future. ED.) Editorial Distortion 1 SIR: Figure 11 of "Distortion in Voltage Amplifiers" in the Febru- ary issue is quite interesting. The "Horrible Example" shows about 0.1 per cent intermodulation distortion at 1 volt output, while the improved circuit shows 10 per cent. A circuit diagram illustrating the good engineering practice needed to achieve this result %mould be enlightening. TUNG-SOL W. H. FROLICS, M. D., Steptoe Valley Hospital. BEAM East Ely, Nevada.

SIR : POWER I have read W. B. Bernard's article "Distortion in Voltage Amplifiers," in the February issue, with great interest, and with AM PLI FI some dismay, particularly in regard to the curve of Fig. 11, page 55. As I interpret the curve, the improved circuit gives very much more intermodulation distortion than the unimproved cir- If you've been looking for an audio output tube that's stable cuit. This is just the type of "improvement" that my little under the most severe conditions -completely dependable - nephew makes in some of his experimental amplifiers. then this is it! The Tung -Sol 5881 is rugged both mechanically and It appears that the curve is either an extreme attempt at hon- esty, so that Diogenes can blow out his lantern and go back to electrically -and directly interchangeable with the 6L6. his barrel ; or that there is a drafting error somewhere. Which? In creating the 5881, Tung -Sol engineers have made lavish use RONALD L. Ives, of the design and production techniques which have proved them- 5415 Main St., 21, N. Y. selves over the past fifteen years -zirconium coating over the Williamsville we did it again. But this time we can't blame the drafts- metal plate and pure barium getter to effectively (Well, carbonized man or the author. We rechecked the author's curve, and found absorb gas for the life of the tube -gold plated wire to minimize that we had made an erroneous notation before sending it to the grid emission. These are but a few of the major design improve- draftsman. We bow our editorial head in shame until the next ments in the 5881. similar error occurs. Seriously, we have requested Mr. Bernard to supply us with the improved circuit to enlighten our readers Tung -Sol produces the 5881 under laboratory conditions, to and ourselves. ED.) assure peak efficiency and maximum uniformity. You'll find this tube has the stuff to take the whole range of audio service require- Frudd Resurrected ments from protracted standby periods to repeated heavy over- SIR : The stripped -down, or utility model, circuit schematic ex- loads. So, if absolute reliability is essential in your audio circuits, hibited in conjunction with the disquisition on the Frudd Audio the Tung -Sol 5881 is a "must." Order it from your regular supplier. System ought to prove no more baffling than the Frudd speaker enclosure disclosure. Detailed minutiae in a schematic are of little interest, anyway, to the intransigent audio enthusiast who invariably disregards trivia and introduces his own circuit modi- TUNG -SOL ELECTRIC INC., NEWARK 4, N. J. fications with the utmost savior savior. My particular modifica- a highly in constructing the circuit Sales Offices: Atlanta Chicago Culver City (Calif.) tion, heterodox one, consisted precisely as diagrammed. Of course, as in any high -quality audio Dallas Denver Detroit Newark system, care in construction pays off in performance. I can attest

T ono-Sol mates All -Glass Sealed Beam Lamps, N inlatere that in assembling the circuit only the best components should lumps, Signal Fluahers, Picture Tubes, Radio. TV and not be used. Special rarpose Electron Tubes. I happened not to have available the pair of 211's specified. However, a search under the mattress (my habit of hiding my stock of components in this fashion derives from the war years

8 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com "Bill, that's what I call professional sound"

You'll never know how professional the sound you record on your tape recorder can be, until you use Soundcraft Magnetic Recording Tape. You'll be thrilled by Soundcraft t.igh- fidelity, delighted by the true- to-life reproduction. Soundcraft engineers are engaged in ccnstant research for new methods, materials, processes. As a result, SOUNDCRAFT MAGNETIC RECORDING TAPE sound engineers throughout the industry - recording studios, radio and television stations, motion picture studios Top quality for top fidelity. The kind of high -fidelity demand Soundcraft Magnetic Recording Tape for the you always associate with professionals. - performance perfection they need. Next time you visit your nearest dealer, ask for Soundcraft Tape. Hear for yourself the professional FOR HOME MOVIE MAKERS! results of the sound you record. Wonderful Way to Make "Talkies" REEVES Soundcraft Magna- Stripe* lets you make sound movies as easily and inexpensively as silent =alms. Add sound to old silent filns. Erase and SOUNDCRAFT.. change the sound any time at all! Dept. B, I O East 52nd Street, N. Y. 22, N. Y. Magna- Stripe service is availaale to you at your photographic store. FREE! SOUNDCRAFT BOOKLETS Ask your dealer abou it. Compete iitormation on Soundcrcft

T .M RS. Magnetic Recording Tape and Magna -Stripe. Ycurs for the asking - just write? www.americanradiohistory.com during which electronic parts shortages drove the service shop next door to larce- nous desperation) did turn up an old WD11. (That had been under the mattress since CANNON the first World War.) This proved to be quite satisfactory as a substitute for two 211's when operated Class AB% in push PLUGS get good reception pull with itself by means of an ingenious feedback circuit. Details of this circuit will not be given as it is felt that any audio man would prefer to design his own... . This system resulted in one which was far superior to any others I have employed, and I "felt" it give forth with pure, 100 per O SERIES cent fidelity, quite unadulterated by anything else. It is also the first audio system I have encountered that can be operated at all hours without arousing the wrath of one's neighbors. With my previous installation, consisting predominantly of a one- kilowatt final feeding an unduly elaborate speaker network in a cathedral enclosure, I was continually beset by the neighbors' pounding on the floor and ceiling. As I was living by myself five miles out in the country, I found this puzzling and strangely disturbing. It has remained for the Frudd system to demonstrate that for once the experts were perfectly right and that any lowbrows who thought otherwise were la- boring under a gross delusion. I must close now because I have two visitors on the front porch. Apparently they think this is a formal affair, for they are both wearing white coats. NORMAN F. STANLEY, P. 0. Box 895, Rockland, Maine. Book Review F UNUAMENTALS OF AUTOMATIC CONTROL SYSTEMS, by G. H. Farrington. 285 pp. -B1 XKW SERIES New York: John Wiley & Sons Inc., $5.00. Automatic control system design is rapidly becoming the most far -reaching K SERIES branch of engineering, crossing the bound- aries of all the other sciences. Although automatic control systems are not new, their study as a separate subject has only been begun recently. Audio engineers V SERIES are most familiar with them in the form of feedback amplifiers and phonograph speed regu- TELEPHONE RECORDER lators. This book is both fundamental and comprehensive. It is divided into clear logi- WRITE FOR cal chapters which do not include material greatly detailed in other works. In partic- PRICE FOLDER ular it is assumed that the reader has some C -109 familiarity with transient response studies using the Heaviside Expansion Theorem and the unit function. The matter of La- The high quality audio connectors shown place transforms, which by now has been above are available from all Cannon Fran- thoroughly labored in books on mathemat- ics, transients, and is chised Distributors. In their great variety of servomechanisms, not M1 SERIES mentioned although it may be more familiar sizes, shapes and contact arrangements there to many of the post War II engineering is no problem or technical requirement in the graduates. Much material on types of con- radio, sound, TV or related fields that cannot trolled systems controllers, and their re- be met. Cannon plugs are standard on leading spective transfer functions is discussed. makes of audio equipment and microphones. These systems are not always electrical or electrically controlled but include hydraulic and mechanical controls. Three chapters of particular interest are Transmission Lines CANNON ELECTRIC and Distributed Constants, Multiple Con- See Cannon Electric trol, and Plant Analysis. Since 1915 Booth 2 -512 Radio The book is well illustrated and includes Engineering Show, numerous text examples but no exercises Factories in Los Angeles, Toronto, New Haven, Benton Harbor. Repre- March 23 to 26, Grand are given, which might limit its use as a sentatives in principal cities. Address inquiries to Cannon Electric college text. Company, Dept. C -109, P.O. Box 75, Lincoln Heights Station, Los An- Central Palace, N. Y. geles 31, California. -L. S. Goodfriend

10 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com in this room... there's no room for doubt There can be no room for doubt in the continuity and fidelity of your broadcast. Precisely the reason you demand -and get -the best in transmitting and studio equipment. Nor should you compromise with quality in the tape recorder you select. In AMPEX Recorders you will find the same matchless reliability and performance you expect of your transmission equipment ... and for the same reason - they are engineered to the highest professional standards. AMPEX brings you these cost - saving operating advantages: UNINTERRUPTED SERVICE Under the demand of heavy -duty programming, AMPEX Re- corders deliver thousands of hours of unbroken service. Recently a set of AMPEX heads was returned from Honolulu for routine replacement after 11,000 hours continuous use, 17 hours a day. The heads were still within AMPEX specifications for new heads and had several thousand more hours of use remaining. MINIMUM "DOWN TIME" AMPEX Recorders are designed for thousands of hours of continuous operation with minimum "down time," resulting in low maintenance costs and protection from sudden broadcast failures. ACCURATE TIMING AMPEX split- second timing accuracy protects your programs and commercials from embarrassing time overlaps. HIGHEST FIDELITY Even when programs are repeatedly transcribed from one tape to another there is no noticeable build -up of noise level, "wow" or distortion. LONG LIFE AMPEX Recorders are designed and built for years of service dependability. Its recordings match established NARTB standards. When you have an AMPEX, you have a machine built for years -ahead performance. IF YOU PLAN FOR TOMORROW, BUY AN AMPEX TODAY

AMPEX MIMS MAGNETIC RECORDERS AMPEX ELECTRIC CORPORATION 934 CHARTER STREET REDWOOD CITY, CALIF.

AUDIO ENGINEERING MARCH, 1953 11

www.americanradiohistory.com NEW LITERATURE Mastro- Voice, Inc., Buchanan, Mich., will mail free upon written request copies of Bulletins No. 185 and No. 189, describing and illustrating E -V Aristocrat, Reg- ency, and Baronet speaker enclosures, as well as complementary single and 2 -way speaker systems. Also listed and shown is the E -V Peerage equipment console, together with a comprehensive table of various changers, amplifiers, and tuners with YOUR PRODUCTION DEMANDS which it may be used.

THE EXCELLENCE OF Minnesota Mining and Manufacturing Co., 900 Fauquier St., St. Paul 8, Minn. discusses uses of "Scotch" electrical tapes in industrial and house wiring, under- ground cable splicing, and other heavy - duty applications in a new 12 -page hand- somely- prepared booklet. In addition there is an interesting passage which covers the Precision use of "Scotch" glass cloth tape with ther- mosetting adhesive in sealing, holding, and insulating where elevated temperatures are involved. This booklet is an impressive example of effective industrial publishing. Prints Available upon written request. David Bogen Company, Inc., 29 Ninth Ave., New York 14, N. Y., under the title "Electronics for Audio -Radio -Television," is now issuing a handsome, 24 -page three - color booklet revealing the design features, specifications, and prices of the company's extensive line of high - fidelity amplifiers, STEP PRINTING public -address systems, FM -AM tuners, boosters, and allied equipment. Irrespec- ELIMINATES tive of your interest in audio, this is a CONTACT SHIFTS book you should have -truly one of the more worthy and complete listings of The sharpness of a print depends on quality equipment to cross this desk in close contact between original and many months. print stock. In step printing at Pre- cision, the two films are absolutely Hudson stationary during exposure. Timing Radio as Television Corp., 48 W. 48th St., New York 36, N. Y. has just re- and effects are produced without leased a new catalog devoted in its en- notching original. tirety to sound reproducing equipment. Intended essentially for music lovers and high -fidelity enthusiasts, the catalog is a complete directory of fine audio equipment, including information on public ad- YOUR ASSURANCE OF dress systems, intercom systems, and replacement parts. Available free upon request by mail or in person at Hudson BETTER 16mm PRINTS salesrooms. 15 Years Research and Spe- enable us to offer service un- Wells Bales, Inc., 833 W. Chicago Ave., cialization in every phase of equalled anywhere! Chicago 22, Ill. describes and illustrates a 16mm processing, visual and wide variety of capacitor types in a new 16 -page catalog. Of interest principally aural. So organized and equip- Newest Facilities in the 16mm to are available to quantity buyers, the booklet is designated ped that all Precision jobs are field customers Catalog C -10, and will be mailed on re- of the highest quality. of Precision, including the most quest. modern applications of elec. Individual Attention is given tronics, chemistry, physics, optics, Wasserlein Mfg. Co., Inc., 126 W. Cass each film, each reel, each scene, sensitometry and densitometry- St., Joliet, Ill., is distributing an illustrated brochure titled "The New Way to each frame - through every including exclusive Maurer- Solder," in which is described the rudi- phase of the complex business of designed equipment -your guar- ments of resistance soldering, as well as processing - assuring you of the antee that only the best is yours its uses for production and maintenance very best results. at in industry. Also contained in the booklet Precision! are operating instructions for using the Wassco Glo -Melt resistance soldering Our Advanced Methods and unit. Requests for copy should specify our constant checking and adop- Bulletin No. 105 -D. tion of up -to -the- minute techniques, plus new engineering Aomiola Distributing Co., 602 W. 52nd principle-. and ..peeial machinery St., New York 19, N. Y. lists the complete line of Acmiola film editing, film viewing, PItF OiSION and sound reproducing machines for professional use in a new sales bulletin. All FILM LABORATORIES, INC. equipment is well described Precision Film Laboratories di- and effectively -a 21 West 46th St., Illustrated. vision of J. A. Maurer, Inc., has 14 New York 19, N.Y. years of specialization in the 16mm Equipto Division of Aurora Equipment field, consistently meets the latest de- JU 2 -3970 Co., Aurora, Ill., recently announced an mands for higher quality and speed. 8 -page catalog especially for the electronics industry. Inclu.ded in the listings are such items as work benches, chassis stands, sales counters, steel shelving and bins, test stands, and warm -up racks. All are priced. Catalogs are available singly for individual use and in quantity for jobber salesmen.

12 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com Easy, Reliable ACOUSTIC MEASUREMENTS

with the SOUND -SURVEY METER e for Acoustic Engineers and Audio Enthusiasts

The Type 1555 -A Sound- Survey Meter is a low -cost, instrument is extremely useful to sales engineers, portable and accurate sound meter. It enables every acoustical field engineers and consultants for pre- audio consultant or enthusiast to make measurements liminary survey work where the refinements of the permitting proper installation of reproducing systems larger Type 1551 -A Sound -Level Meter are in theatres, halls, offices, plants, and living rooms. This not necessary.

The G -R Type 1555 -A Sound -Survey Meter permits There is no substitute for a good frequency - - response characteristic. Yet, the accurate * speaker placement for best coverage determination of overall system response * selection of optimum quantity of ab- is not easily accomplished. orting material for a given speaker housing If sound -pressure level is meas- * adjusting of base -reflex systems ured at a fixed point in a room for best performance as frequency is changed, * detection of room absorption the response curve so ob- defects, enabling corrective measures tained will be very irregu- lar, even in regions of fre- * adjusting of cross-over net- quency where the system works, and correct setting of levels response is actually flat. Sig- in multiple- speaker systems nificant characteristics, such * determining levels for as a "notch" produced by an systems using tone-compen- improperly adjusted cross -over sated volume controls network, may be completely obscured. This effect is a result of rapidly changing standing -wave patterns with changes in frequency. That is, combinations of in -phase and out-of -phase waves cancel and reinforce each other at certain frequencies, causing abnormal "highs" and "lows" in response curves.

With the aid of the pocket -size Sound - Survey Meter, measurements at each frequency may be made at several points within a room, and the results readily averaged. Re- sults obtained may then be put in the form of a relatively smooth curve, representing the aver- Finger -tip control age sound level as a function of frequency, and turns instrument on illustrating the combined effects of speaker and off, selects one of acoustic power output room losses. three frequency character- and total istics, checks batteries - Such results represent the performance of the sound-pressure level is speaker system in its setting and thus help deter- simply the sum of meter and mine effects due to absorption, room -dimensions, attenuator readings - range speaker directivity, and standing -wave patterns. is 40 to 136 db. - flush - mounted crystal microphone has good characteristics - For Complete Information Write for the G -R Sound instrument has stabilized ampli- Measurement Bulletin. fier and level indicator. G -R Type 1555 -A Sound -Survey Meter $125

Admittance Meters it Coaxial Elements* Decade Capacitors Decade Inductors tk Decade Resistors * Distortion Meters GENERAL RADIO Cómpany Frequency Meters* Frequency Standards *Geiger Counters Impedance Bridges 275 Massochustts A , Cambria.. 39, Masfachusa/ts, U. S. A. * Modulation Meters tr Oscillators Hr,iSIM[arOe 9JU.S,N,A.on Art CICAOCf 1t.o,S,Sr,ordSI LOS AM JIM III Varian 4 Light Meters tr Megohmmekrs tr Motor Controls Noise Meters it Null Dekdora tr Precision Capacitors Pulse Generaors tr Signal Generators* Vibration Meters* Stroboscopes* Wass Fillers P-H -F Mea.uing Bqui Intent ir V -T Voltmeters tr Ways Analysers tr Polariscopes

AUDIO ENGINEERING MARCH, 1953 13

www.americanradiohistory.com NEW! Audio Photographer's 3 Super Standard Checklist Output EUGENE F. CORIELL Transformers

UDIO TECHNICIANS and hobbyists rack with gleaming panel assemblies is are understandably proud of their not helped by a cluttered test bench A equipment and of course want to visible in the rear. ±1 db 20- 30,000 cycles photograph it for themselves and poster- 9. Make sure all meters and controls ity. posterity are in their desired positions. If a VU High Unfortunately, even won't Efficiency be impressed if the pictures do not do meter is to be shown with the pointer at Small Size justice to the installation. The following mid -scale or other position, move it to checklist is based on considerable ex- the desired point by connection to a perience in "shooting" audio facilities flashlight battery. If the shot is a close - and while it will not make the reader an up, make sure the channel and master gain and VU S- 510 -F, 10 watts expert, it may help him avoid the more attenuators the range common errors of audio photography. selector are set for the VU reading de- Pri: 10,000i1CT- 8,000s1CT 1. Decide in advance exactly what sired. shots are desired and from what 10. Clean up the equipment and the Sec: 16 -852 angles. 2. Make up your mind as to whether room. Make sure that wastebaskets, you are aiming for art or exposition. dangling wires, and other impedimenta Both are certainly legitimate but this are out of sight in the viewfinder. checklist is principally for the latter. 11. Scratches and dents in panels, S- 526 -F, 20 watts 3. People add interest to pictures of racks and table- mounted cabinets show up embarrassingly well on the finished Pri: 6,600QCT- 5,00011CT equipment, but be careful they do not steal attention from the console, custom prints, so take care of these beforehand. Sec: 16 -8.412 installation, etc. Soldering paste covers scratches in 4. Make sure the camera is level, ex- wooden and plastic cabinets, and grease cept for angle shots, and that you get pencils or crayons of appropriate colors what the viewfinder shows. This usually do a pretty good job on metal rack surfaces. (But item 25, in S- 542 -F, 40 watts calls for a tripod which will also avoid see just the blurring often resulting with a hand- case ... ) Pri: 5,00011CT- 4,0009CT held camera. 12. Allow no smoking while the pic- 5. Resist the temptation to use a wide - tures are being set up . . . the smoke Sec: 16 -8 -4g1 angle lens on close -ups. It gets a wide may fog the picture. area into the picture all right, but may 13. Is the hour of the day important Dimensions Wt. introduce considerable distortion. You to the photo? If so, be sure the clock ap- Inches lbs. do not want your turntables leaning at pearing in the picture shows the desired or get rid of S-510-F 2 %- 23/4 -21/a 2 odd angles and bulging at the top. time ... the clock. 6. Some highlights 14. Do certain elements in a close -up S-526-F 433' -31466 -2'/ 3 are desirable. There's nothing like a lustrous sheen to require emphasis-for example, the re- S-542-F 4'i(o -3/16 -3316 5;2 convey the impression of quality audio cording head of a disc recorder ? Experi- gear. Carrying handles, knobs, switch - ment with spotlighting to brighten de- handles, hand-rubbed wooden cabinets - sired areas. Write these are some of the items that should 15. In close-ups, is the apparatus to be shined up for highlights. be shown alone, or in its normal setting? today 7. Be careful that highlights do not Sometimes a shot of a console is more for the obscure equipment details you want to effective if it is framed by portions of stand out. If flash bulbs are to be used, the adjacent racks and turntables nor- new test for highlights in the wrong places mally associated with it. 1953 by holding floodlamps in the proposed 16. What about shooting through con- flash bulb positions. Attenuator dials trol room windows? Such pictures are Peerless and meter faces are often obscured by often spoiled by glare and multiple images reflected from the inclined double Catalog the glare of highlights. If changing the Now in Stock lighting positions or angles does not panes. Make sure the windows are clean, help, try a light film of vaseline on the and then experiment with lighting on offending areas. both sides of the glass. By using photo- 8. Look out for undesirable back- flood lamps instead of flash bulbs, the grounds which have spoiled many a pic- lighting can be adjusted exactly as re- PEERLESS ture. Keep them out by careful choice of quired before the shutter clicks. Images locale and angle, proper depth of focus, reflected to the bottom of the panes Electrical Products adjustment of lighting, and careful from unimportant surfaces like check- cropping (cutting out undesired border ered -tile foreground floors can be elim- areas) with subsequent enlarging if inated by covering that portion of the A DIVISION OF necessary. An impressive speech -input floor with a dark rug. 17. If considerable detail is wanted on patch panels, omit all patch cords. If 9356 Santa Monica Blvd., Beverly Hills, Calif. * Major, USAF; Radio Technical Of- the latter must be used for effect, use 161 Sixth Avenue, New York 13, New 'fork ficer, Armed Forces Information School, Fort Slocum, N. Y. (Continued on page 70)

14 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com SILECTROC-CORES... BIG or LITTLE ...an.y>quuiitity and any size

For users operating on government schedules, Arnold is now producing C -Cores wound from 1/4, 1/2, 1, 2, 4 and 12 -mil Silectron strip. The ultra -thin oriented silicon steel strip is rolled to exacting toler- ances in our own plant on precision cold -reducing equipment of the most modern type. Winding of cores, processing of butt joints, etc. are carefully controlled, assuring the lowest possible core losses, and freedom from short -circuiting of the laminations. // W'j' We can offer prompt delivery in production quantities-and size is no object, from a fraction of an ounce to C -Cores of 200 pounds or more. / Rigid standard tests -and special electrical tests where required -give ' pA,966° AS:e you assurance of the highest quality in all gauges. Your inquiries ' n/) are invited.

Al .00 THE ARNOLD ENGINEERING COMPANY SUBSIDIARY OF ALLEGHENY LUDLUM STEEL CC= :PORATION General Office & Plant: Marengo, Illinois

DISTRICT SALES OFFICES

New York: Empire State Bldg. Los Angeles: 3450 Wilshire Blvd.

AUDIO ENGINEERING MARCH, 1953 15

www.americanradiohistory.com EDITOR'S REPORT

AUDIO FAIR -LOS ANGELES removed the grille cloth and trim, increased the port dimensions to 11 by 22 inches, using a saw attachment WELL, 111EY DID II ! -\'ter a series of impossible on his electric drill, so as to permit getting his head predictions as to the attendance they would have and shoulders inside the box to unbolt the precious at the Audio Fair in Los Angeles, they even speaker. Remember, this front panel was a one-inch went further and beat the New York attendance record slab of slate. by almost 50 per cent. No matter what you say, you The remainder of the box remains in the house, can't beat those Californians -and this from one who where its new owner is using it as a woodbox, since it hails from there, many years ago. is right next to the fireplace. And our reader is looking We can't help taking our collective hat off to the boys all around Montreal for a 30 by 40 inch slab of half to on the \\rest Coast, though, for their concentrated ef- one -inch slate. fort in putting over a new event in their city. Perhaps Our first reaction to this is that the enclosure must "the four -year build -up of interest in the whole idea of have been pretty good to warrant so much work, and we 'exhibiting audio equipment in a situation where it could invite readers' experiences with similar installations. be heard as well as seen served to swell the desire of Our second reaction is simply one of reminiscence-we the Southern California audio hobbyists and music lov- once sold a house which had an eight cubic foot bass ers into a great flood which was unleashed when the , reflex enclosure built in -wood, of course, but quite ;doors opened on the Audio Fair -Los Angeles for the solid. The new owner sawed out the front panel and first time. used the opening as a niche to accommodate his six -tube The Los Angeles Section of the Audio Engineering open-backed radio console. Society deserves plenty of credit also for its establish- At this late date, we wonder what the effect of such ment of an Industry Advisory Council to work with a niche was on the frequency response of the radio set. the Fair officials in putting over the entire show. It indicates what can be done when enough people put their shoulders to the wheel simultaneously with the benefit FM STATION PROMOTION of the whole industry at heart. One interesting method whereby listeners to a favorite FM "good music" station may help to ensure the SOLID LOUDSPEAKER ENCLOSURES continuance of broadcasting has been inaugurated by KISW -FM, in Seattle, Washington. In a letter ad- With what appears to be good reason, one of our dressed to subscribers to the monthly program maga- British contemporaries has been talking for years of zine, KISW listeners are described as a minority among a conventionally shaped corner bass -reflex enclosure radio listeners in the area, but they are of the type of constructed of masonry as the ultimate in speaker minority who support the symphonies, the art museums, mounting. From an abstract viewpoint, this idea of G. the drama productions, and the good music programs A. Briggs' seems to be valid, yet relatively few of us in a city. Since the station's commercial revenue is in- have the courage to try it out-perhaps because of not sufficient to meet operational costs, some other means owning our homes, or perhaps because it seemed to of augmenting the income is necessary. be too much work, or perhaps because we weren't com- One solution to this emergency that appears to be pletely convinced. However, we can't help but feel a workable is the formation of a KISW Listeners' Com- little sympathy for one of 4 's readers who was con- mittee which would purchase KISW broadcasting time. vinced and who did have the courage to build such an The Listeners' Committee will therefore become a arrangement in his Vancouver, B. C., home. This en- KISW advertiser, and money raised by the Committee closure consisted of an eight- and -one -half cubic foot will not only meet the station's operating deficit but bass -reflex speaker cabinet constructed adjacent to a will enable the station to extend and improve its pro- fireplace in the living room, and housing a well -known gramming. 18 -inch British woofer with a free -air cone resonance Listeners can join the Committee by mailing their of 27 cps. With a port area of 54 square inches- dimen- subscriptions in care of the station. If KISW is worth sions being six by nine inches -his enclosure exhibited the price of a one-dollar movie ticket per month, listen- two resonant peaks of equal intensity at 30 and 40 cps. ers are asked to send in twelve dollars ; if it is equiva-

The box ( ?) was constructed of . Zonolite concrete lent to a theatre or concert ticket per month, they are poured around asbestos cement -board forms, and with asked to send $36 or $48. The first two dollars will be the front panel of one -inch slate. used for a subscription to the monthly program maga- Nothing was wrong with this installation except zine-or a renewal thereof -and the balance goes into that our reader obtained a new position in Montreal, a fund to be used to purchase broadcasting time. necessitating the sale of the Vancouver house. Removal Many music lovers would welcome an opportunity to of the enclosure would have involved considerable ex- aid in the furtherance of this type of broadcasting, and pense in new carpentry, painting, and so on, but leaving if such a plan were put into effect in many stations of the 18 -inch woofer was unthinkable, as we would all this type throughout the country, it is probable that agree. some of the financial problems would he alleviated. We Therefore, using considerable ingenuity, this reader shall watch with interest the results of this plan.

16 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com " a7 la nie -2/ Pf ,/1 ... it comes to you in the subtle shading of a piano .. . in the clean brilliance of violins, the purity of a flute. Your ear detects the sweet mellowness of cellos. the roundness of a clarinet .. yes. even the iridescense of clashing cymbals. And, as the symphony swells to crescendo. its dynamic energy acids a flood of color to your musical canvas.

For those who can hear the difference. these are the elusive pleasures that often remain hidden in the grooves of fine recordings. These are the thrilling new listening experiences that are released for your enjoyment when you use quality components by Pickering.

PICKERING COMPONENTS y4 Gloóe telo cast 'teait t'li/tence "

P I C K E R I N G and company, incorporated

Pickering High Fidelity Components are available through leading Radio Parts distributors everywhere; detailed literature sent upon request. Address Department A 1

Oceanside, L. I., New York 1111! I!I,I!II1!

AUDIO ENGINEERING MARCH, 1953 17

www.americanradiohistory.com "Check your air, Sir?"

Air compressor and tank are at right. Long cyl- inders on rack dry air before it enters cables.

He's checking the air pressure in a branch cable, one of scores serving a town. The readings along the cable are plotted as a graph to find low -pressure points which indi- 1 cate a break in the protecting sheath.

To keep voices traveling strongly through telephone cables, you have to keep water out. This calls for speed in locating and repairing cable sheath leaks -a hard job where cable networks fork and branch to serve every neighborhood and street.

At Bell Telephone Laboratories, a steam of mechanical and electrical engineers devised a way to fill a complex cable system with dry air under continuous pressure. Pressure readings at selected points detect cracks or holes, however small. Repairman can reach Master meters keep watch over the various cahle networks which leave a telephone office in all the spot before service is impaired. directions to serve a community. Air enters the system at 7 pounds pressure, but may drop to 2 pounds in outermost sections -still enough to It's another example of how Bell Laboratories works out ways to keep dampness out. keep your telephone service reliable -and to keep down the cost to you.

BELL TELEPHONE LABORATORIES

Imp oving telephone service fo America provides careers for creative men in mechanical engineering

www.americanradiohistory.com Effect of Load Impedance on Magnetic Pickup Response

NORMAN PICKERING

A discussion of operating conditions for the four popular types of magnetic pickups, together with a series of useful curves showing the effects of resistance and capacitance across the pickup on the over -all frequency response.

AUDIO SYSTEMS DESIGNERS and users ducers, at certain frequencies, two or are always greatly interested in three playings may make a particular frequency response; in fact, one band unfit for further use. The mechani- might say that they are obsessed with o cal impedance of many reproducers is it. And well might they be, since nowa- T such that at very high frequencies with days it is taken for granted that any E VOLTAGE MEASURED AS 'MECHANICAL RESPONSE' small stylus radii, inelastic deformation audio system worthy of the name will OF THE PICKUP of the record material may occur. have a frequency- response characteris- L INDUCTANCE OF THE PICKUP COIL tic which is asymptotic to perfection. RA. RESISTANCE OF THE PICKUP COIL AND LEADS Another more cynical reason has often RL LOAD RESISTANCE ACROSS THE TERMINALS Mechanical Response been advanced to explain the general C TOTAL SHUNT CAPACITANCE BETWEEN PICKUP TERMINALS it is not the purpose of this paper to and devoted attention to frequency re- analyze the situation sponse: existing in the it is so easily measured. mechanical system of the pickup. It will The accepted procedure for measure- Fig. 1. Equivalent electrical circuit of a mag be shown that whatever the basic re- ment nctic pickup. of this parameter is to apply an in- sponse of the pickup, however, it will be put signal of known amplitude and fre- altered by the following electrical cir- quency and to measure the amplitude of Even if we ignore cuit, and such modifications may have the output signal at each frequency. The "absolute" re- a harmful sponse, then, how do we or a corrective effect upon difference between input and output sig- determine even the frequency response. nal amplitudes is the relative frequency response of a the absolute gain of If a frequency record is played by a pickup to a fair ? the device, when due allowance for im- degree of accuracy The given pickup, mechanical signal source is the open circuit response pedance ratio has been made. When all obviously at the pickup terminals gives of these of prime importance, and for practical the desired differences have been plotted information about the way in which against frequency, measurements in the field is invariably me- a frequency- response chanical excitation of the stylus curve results. If the a special phonograph record. This rec- tip is device being meas- converted to electrical energy. This, ured is an amplifier it is ord may he an ordinary "frequency" for a simple matter lack of a better term, might be called to achieve great accuracy. As soon as record, a "glide- frequency" record or a "sweep- frequency" the "mechanical response" of the pickup. a transducer is involved, however, the record. The usual This measurements become frequency record consists of a number response curve must be added to much less reli- the electrical response about to be disable, although hardly more difficult to of bands of discrete frequencies recorded make. at what is hoped is a known amplitude. cussed to give the complete frequency The glide record traverses the indicated response curve of the reproducer. Transducers frequency band at a slow rate, covering all of the frequencies For one thing, absolute gain has no between the start- Electrical Response meaning in transducer measurements. ing and the final one. The sweep record Figure 1 gives a very close approxi- It is necessary to settle arbitrarily on a does the same thing, but at a rapid rate (usually about 20 times per second) so mation to the equivalent electrical cir- definition of gain in order to compare cuit for a magnetic pickup connected transducers. For a phonograph pickup, that an oscilloscope can be synchronized to to the sweep rate and the amplitude - an amplifier. for example, "absolute gain" might be: The microwatts frequency characteristic observed di- useful signal voltage is that de- output per centimeter per veloped across RL. second rectly on the screen. r.m.s. velocity at the stylus tip. Each Even this is incomplete, though, since of these records is useful -and each is subject to considerable no allowance has been made for the error. Network Equations mechanical impedance at the stylus tip. The fixed -frequency record is the only Whenever such definitions are pro- one which can be calibrated, and this The total impedance in the circuit is: posed they usually meet with an apa- procedure must be carried out on each thetic reception for one or more of the pressing if precise results are to be Ra obtained. The general willingness following reasons: 1. It is hard to agree to Zt = jwL + Ro + C) rely upon frequency records indicates a on units, since metric and English units RL are all mixed up in the lack of awareness, on the part of the coC recording busi- user, of the many ness. 2. Most engineers feel that possible chances for pickup error in which becomes: efficiency is not important, since ampli- this method of measurement, yet what is the poor fellow fier gain is cheap. 3. Absolute gain meas- going to do? (RLw'LCC RoRL 1 About all that is possible is to purchase (RoRL +0+ j urements require much care and some Zt relatively expensive equipment. a well -made record which shows a "flat" light -pattern and to discard it as Pickering and Co.. Inc.. Oceanside, soon as the noise level shows that severe N. Y. wear has taken place. With some repro- If E is assumed to be unity, the current

AUDIO ENGINEERING MARCH, 1953 19

www.americanradiohistory.com in the circuit is pacitive component, the frequency re- 100K E sponse may be calculated from Eq. (2). Figure 2 shows the results of such cal- SOK Ze r0K RL- culations for a pickup of 150 millihenries C inductance and 600 ohms resistance. It 70K will be becomes RoRc) seen that the response 60K ( RaRc+C)+j(R`w'L asymptotic to 6 -db- per -octave roll -off at the high frequencies, and this fact ° 50K The voltage across the parallel combina- may be used to advantage in equaliza- 40K tion of C and Ri is /Zr where tion circuits for pre- emphasized record É30K characteristics. It will further be noted 1 20K - j RL that the low-frequency level of the vol- mC 10K0 Zs - tage output is uniformly attenuated be- 100.200 .300 400.500 .600 .700.000 .900 RL-j(mC) cause of the resistance Ro of the pickup COIL INDUCTANCE HENRIES coil. This constitutes a practical limit Multiplying I by Zs, the signal voltage to the amount of attenuation which can across the load becomes: profitably be done with only a resistor Fig. 4. Nominal impedance of a magneti pickup as a function of coil inductance E out= RL+ jmRt'C [RL+Ro-Rtro'(2LC+Roc')] + j [w(RL'C+2RLRoC+L-RiVLC')] (1) ing some capacitance shunting the pickup coil. Since virtually all high - When C = 0, the expression becomes across the terminals. In cartridges which impedance installations have one pickup RL have a high ratio of L to Ro, more high - lead grounded, it is the sum of all the E out= frequency attenuation can be achieved RL +Ro+ jtaL (2) capacitances from grid to ground which before low- frequency losses exceed a is the value of C in Fig. 1. On inspection it can be seen that the practical maximum (say 4 db). Referring to Eq. (1), it will be seen output voltage in Eq. (2) will fall off at Figure 3 shows the frequency re- that C figures prominently in the fre- high frequencies unless RL is very large sponse for a cartridge with a high ratio quency response of the cartridge, but compared to 2 n f L. It is not so easy to of L to Ro. L is 0.472 henries and Ro since it appears both in the numerator tell from Eq. (1) exactly what is likely is 370 ohms. It will be noted that the and in the denominator, and both posi- to happen. effect on low frequencies is very much tively and negatively, it is difficult to less than in the cartridge of Fig. 2. see by inspection what the net effect Practical Values This information gives a good indica- will be. It is in order at this point to examine tion of the nominal "impedance" of the Since C always occurs with RL, it is the equivalent circuit and assign prac- cartridge. Since the generator imped- apparent that the factor RLC is more tical values to the parameters. The user ance is reactive, the load resistance for significant than the absolute value of C. has no control over Ro and L, so the flat response will depend on the induc- It may be of interest to examine actual values found in four popular pickups tive element. This is usually specified by installations in order to determine pos- will establish the region of operation the manufacturer to include effects of sible actual values of C encountered in generally encountered. mechanical response, but for a working practice. figure, the nominal impedance of the cartridge will be the value of 2 re fL at Practical Values of Capacitance TABLE I Eo =1.25 x 10' (approximately 20,000 Inductance and Resistance of cps). At this point the electrical re- The Miller -effect capacitance of vari- Typical Pickups sponse will be down 3 db. Figure 4 ous input tubes is listed in Table II. The indicated L Ro shows the nominal impedance as a func- tubes are those usually en- Pickup countered in phonograph preamplifiers Audak L -6 0.780 Hy. 630 ohms tion of coil inductance. This illustrates clearly how the pickup with 780 milli - used for magnetic pickups. G. E. RPX -050 0.470 Hy. 370 ohms The input connection to the preampli- Pickering 140 henries inductance can have a nominal & 120 0.150 Hy. 600 ohms impedance of 0.1 megohms, although its fier is usually made by means of shielded Clarkstan 0.720 Hy. 1660 ohms d.c. resistance is only 630 ohms. wire. The capacitance per foot of various types of wire is shown in Table III. Effect of Capacitance In addition to these capacitances, there Frequency Response with Resistive Load It is impossible to have a cartridge is generally an additional capacitance of When the load has no appreciable ca- connected to an amplifier without hay- [Continued on page 60]

10 10

_ " RESISTANCE -¡ -- -'LOAD LOAD RESISTANCE 20000 0 -

700 0 00 c 10 jj% 10 oM J EO to FREOOENCY RESPONSE CALCULATED G. E. CARTRIDGE WITH VARIOUS LOADS D120 I. 472KKI RF 370 OHMS L 130. RG 600 OHMS

11 . me.. K fOOX MI las OOm las Icsae FREOUENCY IN CYCLES a PER SECOND FREQUENCY IN CYCLES PER SECOND

Fig. 2 (left). Curves showing the frequency response of a Pickering Dl 20M pickup with various resistive loads. Fig. 3 (right). Frequency response of GE RPX -050 pickup with various resistive loads.

20 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com A Power Tube Figure of Merit

WARREN G. BENDER

The author presents a simple method of evaluating power output tubes which takes into account most of the factors which are of importance in any tube application.

IT IS CUSTOMARY to define figures of while a standby for almost a generation, It must be remembered that the Tube- merit in order to have a numerical suffers from the need of a special fila- Manual figures used to derive these means of examining how well a spe- ment voltage and old fashioned socket values assume among other things, 100 cific job is being done. Such figures of requirements. The six -volt equivalent - per cent efficiency of the output trans- merit as the "Q" of a tuned circuit or the 6A3 -has almost been completely former and perfect regulation of the the gain -bandwith product of an ampli- replaced by the 6B4G and 6A5G. Of power supply. The first condition will fier stage are typical examples. This these, the latter with its unipotential not effect the value of a comparison. The article attempts to define a figure of cathode brought out to a separate pin, second condition however, will affect merit for power output tubes used in is the more modern and probably more the validity of a comparison between home amplifiers, and to compare on this preferable tube. class A and All operation if the regula- basis the tubes commonly used for this The 6AS7G suffers because of the ex- tion of the power supply is not perfect. application. tremely high driving voltages required. From this point of view, when using a The following characteristics of The other triodes listed with their some- conventional power supply, class A power tubes are evaluated in the figure what better figures of merit include those operation, with its smaller current vari- of merit: power output, driving voltage, types whose use is becoming more and ations with signal, is distinctly advan- distortion, and internal impedance. more popular. tageous, although schemes to regulate Other factors such as cost and ease of Of particular interest is the triode - the screens of beam power tubes in class eliminating hum, for example, do not connected 6AR6, which in this evalua- AB. do much to decrease the advantage appear in the figure of merit, and must tion seems to be a very desirable tube of class A operation. be taken into account separately. for future exploitation. All reference to the triode vs. beam - Since amplifiers for serious home use Beam -power tubes in general, with power controversy has been purposely are almost without exception, push pull their modest drive requirements and omitted. The figures do not show any in operation, the evaluation of the figure good power sensitivity, average a bit clear advantage for either type. It is felt of merit is in every case for two push - better than triodes. It is significant to that this is a realistic representation of pull tubes. Also since home amplifiers note the high figure of merit obtained the situation. The high power sensitivity are considered, only A and All opera- by class A 6L6's which are very com- of beam power tubes makes the application are tabulated. monly used. tion of larger amounts of negative feed- The value of the figure of merit is Non -beam-power pentodes which are back easier, which makes up for the given by: less modern compare rather poorly with higher generator impedance of this type (100D) beam power tubes. Class A 6L6's at 10.5 of tube. FP watts output have a figure of merit of It is interesting to note the correlation RL E0 1.75. The figure of merit of class A between high figures of merit and popu- where 6K6's at 9.8 watts is only 1.54. larity of application. The use of this If into is com- F = Figure of Merit operation AB, allowed the figure of merit enables a numerical figure of merit increases markedly, of various P = power output in watts al- parison of the desirability though this increase is attended with tubes consideration for a given D = distortion at rated output under greatly increased difficulties of If it is desired to evaluate new RL = load impedance in thousand ohms driving amplifier. power, power supply requirements, etc. tube types or other operating points, the Ea = peak grid driving volts. Fixed -bias 6L6's with 47 watts of out- calculations to obtain a figure of merit The available power appears in the put power have a figure of merit of are straightforward and easy. Thus it numerator of the figure of merit ; thus 16.82. Similarly connected KT66's yield is a simple matter to keep the table of a larger amount of power results in a a value of 11.9. figures of merit up to date. larger or more desirable figure of merit. Conversely the peak grid driving volt- TABLE I age and the load impedance, which is a Figurc of Merit function of the internal impedance, appear in the denominator. Thus, the fig- Triodes Class Bias Voltage Power (watts) Figure of Merit

ure of merit is an index of the power 2A3 -6B4 etc. AB 1 Self 300 10 1.22 available as modified by other factors 2A3 -6B4 etc. ABI Fixed 300 15 3.94 which make the use of the tube more or 6AS7G A Self 250 13 0.83 less desirable. The larger the figure of 6AS7G A Self 200 11 I .47 merit the better is the tube. 300A A Self 450 35.6 4.90 A number of values for commonly KT66 ABI Self 250 4.5 4.42 KT66 AB1 Self 450 14.5 4.38 used is tubes given in Table I. 807 -1614 AB1 Self 400 15 5.40 The calculations for the 2A3 family 6AR6 A Self 400 20 14.5 show a marked preference for the use Beam Power of fixed Class Bias Voltage Figure bias. However the choice of bias Tub es Power (watts) of Merit

method must depend on the decision of 6V6 AB 1 Self 285 14 4.45 the designer as to the return for the 6V6 -6AQ5 ABI Self 250 10 3.17 extra trouble of providing fixed bias. KT66 AB 1 Self 250 17 I 1.30 Within this group of tubes are many KT66 AB 1 Self 450 30 5.05 differences which are not reflected in the 6L6 -5881 A Self 270 18.5 9.06 common figures of merit. The 2A3, 6L6 -5881 A Fixed 270 17.5 9.80 6L6 -5881 AB 1 Self 360 24.5 4.58 6L6 -5881 ABI Fixed 360 26.5 8.78 * 62 Park St., Tenafly, N. J.

AUDIO ENGINEERING MARCH, 1953 21

www.americanradiohistory.com The Selection of Tone-Control Parameters

EDGAR M. VILLCHUR*

Proper design of tone controls requires a study of the conditions which must be cor- rected. The author delineates these conditions, and explains the requirements for each.

ARIOUS TONE- CONTROL circuits with given transition frequencies' 15 and i i iilin I I I lii rates of boost or cut have been ex- - -- SPEAKER RESPONSE (PRESSURE) - TONE CONTROL RESPONSE (VOLTAGE) ' 1 tensively discussed in technical litera- RESULTANT SPEAKER OUTPUT ture. Little has been written, however, HO - - about considerations involved in the 3 selection of the response -curve param- _s I eters, which sometimes seem to be Fig. 3. Resultant fre- chosen more or less arbitrarily. While quency response of "flat" power an audio system us- rl\I I amplifier stages are care- ing a commercial '. fully designed for $ r LLL an audio- frequency speaker in the $50 / response which is kept to a maximum J class and the treble s l/1 I random deviation of a fraction of a boost of (A), Fig. 1. ' i decibel, improper tone compensation Ill (either manual 10 or automatic) in the t1! same amplifier may introduce, or leave i uncorrected, very large inaccuracies of 'S 'coxM frequency distribution relative to the IM IO M perceived original. These inaccuracies FREQUENCY IN CYCLES PPER SECOND have on occasion completely over- shadowed the benefits of the above -mentioned careful design, and have become a primary factor in determining over -all volume level. The inclusion of such which allows for equalization of almost quality. circuits does not make variable tone any frequency conditions, or he can Fixed tone equalization is used when control superfluous, since there are reduce the flexibility of control, choos- the frequency characteristics for which many unpredictable conditions for ing compromise response curve param- compensation is being made are con- which it may be desirable to adjust the eters which are capable of producing stant. Modern home reproducing sys- frequency response of the reproducing approximate compensation for those tems contain several fixed or auto- equipment. conditions most likely to be encountered. matically variable audio equalization The designer of fixed equalizers does The degree of tone -control complexity circuits associated with FM pre -em- not ordinarily have to worry about accepted in non-professional equipment phasis, recording characteristics, pick- what parameters to use; with certain has increased quite a bit since the day up frequency distortion, or changes of exceptions his transition frequencies, of the single treble -cut switch, and the and the required rate of boost or cut, most common arrangement in current Contributing Editor, AUDIO ENGINEER- ING. have been exactly determined by his audio amplifiers is a two- control, con- problem. In contrast a tone-control de- tinuously variable system. This allows I The transition frequency is the inter- section of the theoretical linear slope of the signer must furnish the means for progressive cut or boost of either bass response curve (a slope which the actual correction, by the same circuit, of all or treble, but no independent control curve only approaches) with the frequency sorts of signal aberrations. He can of the reference frequencies at which axis -see Fig. 5. either provide a complex control system the response curves begin their slopes.

25 23 20' 20 13 HS ;;y10 10 __- ... íZ 5O -5 z 0 i _ . __ ó _' '5 S 1 _- M ó 10 I

-15 1S

20 20

YS 23

ao ' mom M M IM IMM 14 MM MIMI > FREQUENCY IN CYCLES PER SECOND FREQUENCY IN CYCLES SECOND

Fig. 1. (A), Voltage response curves of a typical commercial tone control circuit of the R -C type, maximum positions. (B), Voltage response curve of a commercial tone control circuit of the L -R -C type, maximum positions.

22 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com A circuit which introduces a progres- operator's adjustment of tone controls This factor, referred to as the Fletcher - sive response slope rather than uniform is in the nature of a search for maxi- Munson effect, will be discussed in the elevation or depression of a whole band mum fidelity to the perceived original, paragraphs devoted to bass boost. of frequencies, besides being of far the psychological mid -point ceases to Equipment treble deficiencies are simpler design, provides the desired have much significance. Tone control usually most severe in electro- acoustic form of compensation in most applica- becomes tone compensation, and the devices such as loudspeakers, pickups, tions. It is common although not uni- problem of response -curve parameters and recording heads, but also occur in versal practice for dual tone controls revolves about the question of what the coupling circuits in audio or inter- to use approximately the same tran- controller must be equipped to compen- mediate- frequency amplifiers. sition frequency region, usually at or The worst offender in a given system sate for. In the following discussion it below 1,000 cps, for both bass and is ordinarily the loudspeaker. In Fig. 2 will be treble variation. Figure 1 shows the assumed that the amplifier is manufacturers' published on -axis re- response curves of two such tone con- being designed as an independent unit, sponse curves for six speakers in dif- trol circuits employed commercially. and that the brands of components with ferent price ranges are plotted. Al- The justification for selecting this which it is to be used are not known. though the performance represented by these curves will vary greatly under different acoustical conditions t h e graphs may be taken as indicators of III f I I I I IIII a general is 0 !lEItlVOSfD REFERENCE LEVELS trend. There one feature SOFO° OF 50 AND 110Mw CURVES OF which all may be seen to have in corn - S0 rEETCKII-MJN50r1 EQUAL LOUDNESS- CONTOURS. mon, and which is characteristic of the great majority of cone loudspeakers W Vzo with high- frequency droop; the fre- W; e0« quency region of the first two octaves . Fig. 4. The 50- and , 80 -phon equal loud- above 1,000 cps, far from being attenu- >Ñ ~ `%N. .1 - ness contours (from ated, is accentuated (because of the _ -1100.°: Fletcher and Mun- new resonances introduced by cone o son) superimposed. break -up), and treble droop does not `. begin before 4,000 cps or higher. This fact has a significance beyond the ob- ¢1p vious implication concerning compensation for speaker deficiencies. Any losses in the first two treble octaves s I« IM IMO '00°O which are likely to be met with from FREQUENCY IN CYCLES PER SECOND other causes will probably be compensated or even over -compensated by speaker characteristics. reference frequency region is that it is Treble Boost Crystal phonograph pickups have a considered psychologically "neutral" in The most common purposes for which typical velocity response above a few pitch. It has been pointed out that 800 treble boost will be needed are: hundred cps which decreases with fre- cps is the geometric mean between 40 quency quite regularly up to a 1. Compensation for treble rather and 16,000 cps, frequencies which may deficiencies sharp cut-off somewhere between 4,000 be taken as nominal limits of hearing in associated reproducing equipment. 2. Compensation for treble deficiencies and 10,000 cps. When this regular droop under average conditions. Since the in program material. does not conform to the desired record- perception of frequency, like that of 3. Compensation for discriminatory ing characteristic further compensation amplitude, closely follows the Weber - acoustic absorption with a frequency is properly provided by a fixed R -C net- Fechner law (in that the degree of characteristic different from that of the work rather than by the tone control. sensation varies logarithmically with hall or studio in which the sound origi- The comparatively smooth and accu- the stimulus) the geometric and not nated. rately predictable slope lends itself to the arithmetic mean of the audible fre- An additional purpose for which fixed equalization, and the recommended quency spectrum is its psychological treble boost has on occasion been con- circuits or necessary data for their de- mid -point. Thus there are about four sidered necessary, but is not, is com- sign are usually readily available from and one -half octaves of useful audio pensation for the variation in hearing the manufacturer. But whether or not frequencies on each side of 800 cps. frequency characteristics associated such a fixed network is provided, the If we assume, however, that the with changes of sound intensity level. treble boost control cannot be designed

'- I rI II I I I / 0.,{ I i_ajIIl f7 1'llI - !MiíliiQiN a = 111,/IIII r1111 = Af1IIIriS1IIi1, VIII !IRSI"'.Jil r,`'i",1 1 üI/I=íI11_ 1 I1 ° !IIrIIII 1 > YT/I1Ir nr 1H 5 --- 11 SPEAKER I11 II Hp( SpEAMER E tKANER I 10 .l Il --- , o --- tJl 12 SPEAKER in In _ E- SISEAEERE - irisdi ¡kIL , , . i RI . MOO « . . . ]0000 II« I00« I« Iae° FREQUENCY IN CYCLES RER SECOND FREQUENCY IN CYCLES PER SECOND

Fig. 2, (A) and (B). Pressure response curves of three commercial speakers in a price range of $20 to $150.

AUDIO ENGINEERING MARCH, 1953 23

www.americanradiohistory.com for correct crystal pickup equalization the compensation will not be used. This except for the second droop, because the unhappy effect is illustrated by Fig. 3, required transition frequency would be in which the tone-control and speaker - well into the bass region. response curves of two high -grade com- The contribution of high -frequency mercial units are combined. losses by other components cannot, of Determination of an optimum transi- course, be predicted, except as to one tion frequency that will best suit the factor ; it may be expected that losses various requirements of treble boost can- will be confined to frequencies above the not be made with precision, but it would second treble octave. A survey of cir- seem that present commercial practice cuit components, recording heads, etc., makes use of a frequency which is at will indicate that it is rare for treble least two octaves too low. The operator droop to set in before 4,000 cps or so. of the set may be impressed with the Even AM broa: cast band i.f. trans- dramatic power of his treble boost but formers provide, at worst, relatively may still be loath to use it. (Some even coupling to 3,000 cps. British manufacturers lean towards Treble in ma- higher deficiencies program transition frequencies for treble Fig. 6. Circuit values to approximate the terial may result from low -grade studio emphasis-one manufacturer uses 3,500 curves of Fig. 5. As many of the values of the equipment, from transmission circuits, cps.) original t circuit as possible have been and from old records. Such losses are A single R -C network can approach retained. almost always associated exclusively 6 db per octave in rate of boost. The with the third and fourth oc- simplicity of the single network is one /or treble companies subscribe. Table 1 lists some taves. good reason for accepting this slope as of the different ways in which the treble The writer has not found a cjuantita- the maximum, and it will prove ample spectrum is or has been treated by rec- tive study which compares the frequency for most purposes, particularly in view ord manufacturers. transmission of typical living rooms with of the fact that treble emphasis brings Although treble recording character- that of halls or studios, although meth- to the fore harmonic distortion in the istics are ideally equalized at the pickup, ods for room transmission measurements higher ranges. If the transition fre- variable pickup equalizers are still the have been outlined.2 Therefore no com- quency is chosen as 3,200 cps-two oc- exception rather than the rule, and the ment will be made on the subject other taves above 800 cps -an insertion loss of tone-control designer must assume that than to mention the fact that room 20 db will produce something less than at least some of the burden will fall on acoustics -notably t h e reverberation 12 db of maximum boost at 13,000 eps, the treble-cut control. If the setting for time versus frequency relationship -may including about 3 db of boost at the minimum treble furnishes close to 6 db be a factor requiring tone compensation. reference frequency itself. These char- of attenuation per octave from a transi- Reference is made to this factor under acteristics seem to represent a reason- tion frequency of 2,000 cps, approximate the heading of treble boost merely on able compromise between the require- compensation for any of the recording the basis of subjective experience, but ments of all factors. The use of an even pre -emphasis curves can be achieved. undoubtedly other compensations are higher transition frequency might be de- also involved. sirable, but would place a greater limita- TABLE 1 When treble boost is needed, then, a tion on the maximum boost of useful high transition frequency is usually de- frequencies that could be achieved with Typical Transition Frequencies sirable. The use of a lower transition a single R -C network. Transition Rate of frequency for the sake of increasing the Records Frequency Boost (cps) (db/ amount of boost available at the upper Treble Attenuation end might prove satisfactory if it were AES Standard Curve 2500 6 not for the marked tendency of loud- Treble attenuation is required for : Columbia 78 & 33 1/3' 1590 6 speakers to emphasize the frequency re- 1. Compensation for varying treble RCA 78' 1000 2.5 gion of the first few thousand cps. A preemphasis in recording. London ffrr 78' 3000 3 transition frequency of 1,000 cps 2. Reduction of record suface noise London 33 1/3' 3000 6 or -frequency EMI lower may cause treble boost and high distortion. 78' - none to accentu- 3. Compensation for rising treble re- Older records none ate a shrillness towards which the sponse of associated reproducing or stu- speaker performance is already inclined, dio equipment. of and needed boost at frequencies above 4. Tonal balance against a thin bass. Settings the treble control which yield 4,000 cps may carry such a penalty that less than maximum attenuation will also, Treble preemphasis in recording in most circuits, automatically shift the 2 E. C. Wente, "The characteristics of varies considerably, and there is no transition frequency higher, correcting sound transmission in rooms," J. Acous. standard, either of transition frequency equalization for some of the records Soc. Am., 7, p. 134, Oct., 1935. or rate of boost, to which recording with more gradual preemphasis slopes. The desirability of equalization for treble recording characteristics prior to the tone control is emphasized by the differences between the transition frequencies of some of these recording .EO----7y, vl curves and the frequencies at which the . » 1111 equipment deficiencies previously dis- =,0- I cussed introduce treble losses. For ex- .,Q I ample, an improperly equalized disc .e Fig. 5. Suggested which has been recorded with a given - 1lll tone control fre- treble characteristic can present an un- quency characteris- satisfying choice between shrill and ° _ tics, controls at muffled reproduction, because the tone maximum positions. i [Continued on page 68] ° PIPii 3 Paul W. St. George and Benjamin B. e0 .. iiii Drisko, "Versatile phonograph preampli- 11 1 111 fier," Aonro ENGINEERING, 33, p. 14, FT TRANSITION FREQUENCY March, 1949. n 4 D. T. N. Williamson, "High -quality ' Ioo w00° ,WFREOENCYD IN CYCLES SECOND amplifier modifications," Wireless World, 58, p. 173, May, 1952.

24 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com Audio in the Year 1693 ALLEN H. FRY`

Accidentally discovered in the New York Public Library during a search for some early papers of Harvey Fletcher, this book compiles much of the audio knowledge of its day.

The Collection and Transmission of Sound THE TREATISE ON SOUND whose title DE page is here reproduced was written ET JURE Acoustical ear -tubes ... work on the in 1693 by Caspar Ringelmann, NATURA principle that sound is normally dissi- probably as a thesis for the doctorate. pated in the free and open air. By using Both acoustical theory and a hypotheti- such a tube the total vibratory movement cal engineering practice are covered. AUDITUS is carried directly into the listener's ear. in the (See Fig. 2.) By listening to a sea -shell Although more profound work ac or large jug one can even hear the re- theory of vibrations had already been sidual sound produced by the otherwise performed by Galileo and Newton, and quiet ambient air. although Bacon's Nowlin Organum had SONI, Along this same line of reasoning, it In Illullri Univc fitate outlined standards of scientific method is possible to construct a building so that which Ringelmann did not always meet, CHRISTIA\- ALBERT1NA, if a person were in one central place he Sut, PrxiLla, could hear everything going on through- the description of contemporary acousti- l C5' (rv5, ri -r;r cal design makes absorbing reading, and out the entire building. Dni. REIHERT» Nova, 1673) is modern devices. SAMUELJS Kircher (in Phonurgia often prophetic of nec non Matherom. on some Acoustic devices selected passages from JCti, Codicis discourses Following are Superior. & Inferior. Prof. Ord, &c. of his which will enable one to carry on the treatise, translated from the Latin fui atatem devenerandi, a conversation from one room to another all Praceptoris (the language then standard for Die 27. Majr, anrd 41 DC .« 111. inside of a house. (See Fig. 3.) Or, out- scholarly work). dnputabit doors between two distant places. CASPAR RINGELMANN The Nature of Sound and Hearing Oldenb WclfphaL Construction of an Artificial Mechanism Sound is an oscillatory movement of x,tx.i..r,.uw. the air activating the ear locally. Typis Joachimi Rcumanni, Atad. Typogr. It will be noted that the device de- The inner ear has the sensory func- scribed below substantially constitutes tion. The outer ear collects the sound the input system of an acoustical phono- and transmits it to the inner. Fig. 1. Title page of the thesis "Of the Nature graph; it has a horn, a diaphragm The motion of the air sets contiguous and Laws of Hearing and Sound" by Caspar across the horn's throat, and bodies in motion. Thus, air movements Westphalia, who stretched Ringelmann, of Oldenburg, a mechanical device attached to the set the tympanum of the ear in motion ; "will dispute" (defend the thesis) on May 27th, this in turn moves the Hammer which 1693. diaphragm. strikes the Anvil. From here on, the mo- to a differ- The term "artificial ear" refers tion is carried by air pressure an actual working model ences. (Note: this is inaccurate; the device which is through the of the human ear. (Figure 4). It may be sound is actually propagated the mechanism of cochlear fluid.) These internal pressure used to demonstrate the hearing process, or in the case of differentials act upon the auditory nerves about a the brain. auditory deficiency, to bring which transmit them to compensation. Vitruviust well explained the nature certain degree of 1. Make a little ring of metal and of sound where he says: "Sound pro- a short increasing form the leftover end -piece into ceeds outwardly in a series of Let the very end of this circular movements. It is as though we appendage. into a pool of appendage be the Anvil (c). were to throw a stone ring with a lightly - placid water.... Starting from the cen- 2. Cover the ter the circles become larger and larger." stretched membrane. 3. Glue or fasten onto the membrane the Princeton, N. J. [Continued on page 56] t A classical Roman architect and writer. Fig. 2. Ear -tubes for voice communication.

ytttttttt1f111tt'g,Hltftt

Fig. 3. Seventeenth century intercoms, also useful as spy systems.

AUDIO ENGINEERING MARCH, 1953 25

www.americanradiohistory.com Auxiliary or Emergency Broadcast Control Room

HAROLD REED

For a total cost of $125, one engineer equipped a small storeroom to ex- tract double duty from idle remote equipment as a fixed studio installation.

THESE DAYS of intense competition was cut through to the main studio and material fed on either of these circuits III the radio broadcasting business, three panes of glass installed to afford can be dispatched to any point, the not to mention the additional bid for sound isolation. This wall, being a studio terminating resistors being automat- advertisers' dollars now being made by partition, was television, it already treated for sound ically removed from the circuit when often becomes necessary for isolation. The radio stations cost for this work, includ- the patch cord is inserted. Figure 1 to effect every possible ing painting economy in their operations. Yet the window frame was gives the layout described above and the $88.00. engineering department is frequently Nothing more was spent on this shows the tape recorder setup outlined faced with increased program and re- room except for varnish to improve the in the next paragraph. cording activities in spite of so- called appearance of the floor. A portable Magnecord tape recorder, economic operations, making the techni- Several remote amplifiers were in the normally used for remote recording cal facilities available entirely inade- plant and rarely were they all in the work, was placed on a small table near the quate to meet the demands of the pro- field simultaneously. These field ampli- 22D amplifier. This recorder is gram and commercial departments. fiers are Western equipped with a high -impedance bridg- Electric 22D models. ing input There are usually enough studios One of these amplifiers was installed and a 603 -ohm output, both on of which appear on screw -type terminal available, but a serious lack of studio a small, badly scratched, desk which was control facilities is generally encoun- strips. For convenience in removing given a coat of commercial -looking and replacing this unit, small tered when numerous auditions, re- green paint. Four connect- hearsals, and recordings lengths of flexible, ors were installed at the rear of the are scheduled, shielded, microphone cable were in addition to the program "on the air." fed chassis. The bridging input is connected Studio control through the wall and terminated in across output #1 of the 22D amplifier equipment is costly, so microphone if anything is to be done to improve input receptacles mounted and the 600 -ohm output is fed to the the in Wiremold boxes. situation it must be on the basis of The control room 30 -ohm microphone input channel #4 making the apparatus ends were terminated in connectors through a 600 -to -30 ohm, 60 -db pad. on hand do double suitable for duty and of using any spare or obsolete the microphone inputs of This provides for recording, through pieces, modifying the 22D amplifier. Two 600 -ohm out- the bridging input, any program mate- these units to perform puts a satisfactory broadcast service. are available on these amplifiers. rial going into the amplifier, and to feed One Flexible cables were such situation as outlined above was connected to these to the amplifier, through #4 mike chan- overcome with the other ends terminated in nel, any tape recording played on the in the following manner. twist Adjacent to one -lock connectors. These connectors recorder. In this way, three studio side of the main plug into receptacles studio was located a small mounted in Wire - microphones and the recorder can be room, 12 by mold boxes and installed 7 feet, which was being used for office on the wall fed simultaneously into the amplifier or, supplies. Arrangements near the desk, from which two shielded if no recording is played, four studio were made to pairs are house these supplies in taken to the main jack panel microphone channels are available. other parts of in the master control the premises and a 48 by 30 inch window room. 600 -ohm The cable from the input of the re- terminating resistors are normally corder is terminated in the same type Chief Engineer WOL, 1000 Connecti- across these pairs at the jack panel end. of connector as the microphone cables cut Ave., N.W., Washington 6, D.C. By means of patch cords, program and they are, therefore, easily inter-

Fig. 1 (left). Diagram showing interconnections between WE 22D Remote Amplifier and a portable tape recorder to provide extra studio cont of facilities. Fig. 2 (right). Block diagram to show connections for transcription turntable and monitoring amplifier and speaker.

26 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com changed. Normally three microphones switch, a push to listen, self -releasing and the recorder input are kept in posi- type is conveniently located on the turn- tion. The 600 ohm output of the re- table top, the amplifier inside the cab- corder can also be fed to either line to inet, and the speaker on the wall near the master control jack panel. the operating position. Suitable circuits For aural monitoring of programs for the cueing amplifier can be adapted and recordings an audio amplifier and from published circuits. loudspeaker are also bridged across the A block diagram showing turntable #1 output of the 22D Amplifier. No and cueing arrangement and monitor- details are given here in regard to the ing system is given in Fig. 2. Con- monitoring amplifier as many published nection between the preamplifier and circuits would be satisfactory. However, the 22D amplifier is shown in Fig. 3, one requirement of the amplifier used and details of the record cueing switch is that it must include a high -impedance wiring is presented in Fig. 4. It will be input so that it does not load the 600 - noted that dual contacts are incorpor- ohm output of the 22D amplifier across Fig. 3. Details of connections between tran- ated in this switch to avoid continuity which it is bridged. scription equipment and 22D remote amplifier. failure. The Western Electric type 92A switch is excellent for this purpose. A Transcription Facilities microphone input channel on the ampli- talkback system is contemplated so that An old transcription turntable' which fier and because these inputs are of a the control operator or producer may had formerly been used for audition low impedance value, and as the ad- talk to participants in auditions and re- purposes, was salvaged. It was in good ditional gain of the first stage of the hearsals via of a small loudspeaker in condition mechanically, but was equip- amplifier is not required, the high im- the studio. ped with a heavy, obsolete pickup pedance output of the phono preampli- It is to be observed that special care arm and cartridge. A lightweight, inex- fier was coupled into the second stage was taken to have the principal pieces pensive, Clarkstan (Pacific Trans- of the 22D through a standard phono of equipment installed in such a way ducer) #212 arm was installed and plug and jack. A gain control was that they would be easily removed for fitted with a G. E. variable reluctance mounted on the turntable cabinet to other uses for which they were intended, cartridge. The arm includes a quick - control the preamplifier output. although the apparatus is normally set- change weight adjuster so that standard So that the operator may cue up a up as described. Inter -connecting cables or long playing microgroove records record before feeding it into the con- are terminated in different type con- can be reproduced. The cartridge trol amplifier, a cue switch, amplifier nectors making it unnecessary to label holder is of the slide -in type and can be and speaker arc provided. The cue any of them to prevent the possibility changed quickly. Two cartridges are of incorrect connections between units. kept available, one with a 3 -mil stylus It has been found that about 90 per cent for playing standard records, and the of the time the equipment is available other with a 1 -mil stylus for micro- when required in this auxiliary control groove recordings. A G. E. phono pre- room. amplifier, #UPX003, with self -con- The total cost, by utilizing component tained power supply was installed in parts on hand, amounted to $125.00. the turntable cabinet to provide the This low cost has provided another voltage gain and equalization to operate program and recording channel, re- the cartridge into the 22D amplifier. lieving the pressure on the other con- This preamplifier should be mounted on trol facilities. Noise, distortion, and sponge rubber and kept as far as pos frequency response characteristics will sible from the a.c. field of the turntable Fig. 4. Wiring of record cueing switch and meet FCC specifications for radio motor. In order not to use up another amplifier. broadcasting stations.

V.W,§

March 23- 26- INSTITUTE OF RADIO ENGI- PONENTS SYMPOSIUM. Presented through SHOW AND CONVENTION, sponsored NEERS, convention. Waldorf- Astoria Ho- cooperation of AIES, IRE, RTMA, and jointly by WCEMA and Western Sec- tel, New York City. Held in conjunction WCEMA. Shakespeare Club, Pasadena, tions of IRE. Municipal Auditorium, San with California. Francisco, California. March 23-26-1953 RADIO ENGINEERING May 7 -9 -Forty -fifth Meeting of the September 1- 3-INTERNATIONAL SIGHT AND EXPOSITION, SHOW. Grand Central Palace, New York ACOUSTICAL SOCIETY OF AMERICA. War- SOUND combined with City. See page 38 for details. wick Hotel, Philadelphia, Penna. Fea- the CHICAGO AUDIO FAIR. Palmer House, April 28-May 1- Seventh Annual NA- tured subject: Sound Reproduction. Side Chicago, Ill. TIONAL ASSOCIATION OF RADIO AND TELE- trip to RCA Laboratories, Princeton, October 14-17 -Fifth Annual Convention ENGINEERING SOCIETY, and VISION BROADCASTERS' convention and N. J., on May 8. of the AUDIO 1953 BROADCAST ENGINEERING CONFER- THE AUDIO FAIR. Hotel New Yorker, ENCE. Burdette Hall, Philharmonic Au- May 18-21 -1953 ELECrlOxtc PARTS New York City. ditorium, Los Angeles. SHOW. Conrad Hilton Hotel, Chicago. October 15-17- ACOUSTICAL SOCIETY OF April 28 -May 1 -1953 ELECrRoxtc COM- August 19- 21- WESTERN ELECTRONIC AMERICA. Cleveland, Ohio.

AUDIO ENGINEERING MARCH, 1953 27

www.americanradiohistory.com The Columbia "360"

PETER C. GOLDMARK

Presenting the inside information about an interesting instrument designed to offer high quality in a ready -made form.

AT THE END of the last war, one of the programs facing the Laboratories was to develop a method whereby recorded music of the highest quality and at the lowest cost could be brought to as many homes as possible. It was apparent that this meant a new system of music recording and music reproduction which, because of the magnitude of the task, we had to tackle sequentially. The first phase of our work culminated in the development of the LP record Fig. 1. The Columbia which became the almost exclusive me- "360" phonograph, dium for recorded classical music, at a as described in the fraction of the cost of the pre -LP al- accompanying article, bums. We then entered the second phase of our development program, which involved creating the mate for the LP record. The latter can carry a sound quality which includes everything the average human ear is capable of hearing. Until now, commercial phonographs did little justice to these records and people in their homes wanted high quality in a compact, entirely self-contained, reasonably priced phonograph which can be placed almost anywhere in a room. He yet this is not what the music lover is properly blended, will approach as or she would also like to be able to bring interested in. We were in search of nearly as possible a lifelike rendition of the instrument home from the store, plug something that would approach the the music originally recorded. Sufficient it into ulti- a wall socket, and play it. To fill mate in music reproduction and felt frequency range naturally is one of these these needs, at the same time reproduc- that the and the instrument ing desired end effect could best has adequate re- virtually everything recorded on the be described as realism. The sponse between 50 and 12,000 cps. Most LP record, the Columbia Columbia "360" has been "360," shown in Fig. 1, records do not contain much usable in- developed. which is the first one of a new series of music re- formation below SO or above 10,000 cps, The term "High Fidelity" is usually producers, represents the beginning to and thus reproducing equipment with associated with wide frequency range, the solution of this problem and in the excessive capability beyond these areas following paragraphs some technical can- unless properly controlled-pro- details regarding the "360" will be dis- duce considerable rumble and surface Vice- President in Charge of CBS Lab- cussed. noise. oratories Division, 485 Madison Ave., New Realism in music reproduction in- Effects such as distortion and inter - York 22, N. Y. volves many ingredients which, when modulation in the "360" were kept down to a sufficiently low limit, but again we did not choose to go overboard. A great deal of attention was concentrated on the most important processes involved in the translation of electrical impulses to sound waves. The phonograph is only 17 in. wide, 10 in. high and 13 in. deep, yet the sound produced compares favorably with many a large "High Fidelity" installation. In designing this instrument, we Fig. 2. Internal ar- found it best to make the loudspeakers rangement of the cabinet with record "take a back seat" and let the enclosure player removed. do most of the work. The sound does not emerge from a loudspeaker in front of the instrument directed straight at the listener as has been the practice to date. We found that in order to approach the illusion of reality in a room, sound should be diffused before it reaches the listeners' ears. Thus, two speakers have been provided facing outward and mounted on opposide sides of the cabinet, as shown in Fig. 2 sound is now

28 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com developed; the arm, made of metal, produces a slight resonance of around 50 cps which plays an important role in the 1111111111111111111111111111 over -all frequency response of the sys- mlIIIIIIC:=I111111::0111I tem. The cartridge has been developed with the Sonotone Corporation and uti- lizes a ceramic element. A rotating needle assembly, Fig. 3, carries two sap- :'1illii::IIII11`CIIii phire points back to back, one with a C:aIIIIICC:IIIIIIimaiI radius of one mil and the other with a radius of three mils. Needles assembles ::IIIIII:IIIIIIC Mil IIy containing a diamond stylus for LP records will also be available. The frequency response of the cartridge -and- Fig. 5. Measured acoustic response curve , arm combination looking into a load of compared with electrical curve of Columbia A is response with 1.0 meg. and 100 µµf, is within a few db 103 test record. Curve maximum treble; B is with minimum treble. of the required reproducing characteris- Solid curve represents the test record. tic when using the Columbia No. 103 Fig. 3. Underside of the tone arm showing the test record as signal source. The car- rotating stylus assembly in the cartridge. The tridge compliance is of the order of 0.9 AINTS ° PP 351.6 x MODEL stylus is rotated to change from LP to 78. 10-6 cm /dyne and the voltage output, ~ the Columbia 103 test record, is 13323 all the in- using 0 radiated practically around approximately 0.5 volts at 1000 cps. The strument (hence the name "360 ") and stylus can easily be changed by any lay- 20 arrives at the listener after it has been man by raising the arm, lifting out the - A- RESISTOR LOAD 16 OHMS bounced around in the room, resulting entire stylus assembly and replacing it in a mixture of many different phases II -SPEAKER LOAD with a new one. 615 and amplitudes. s The "360" phonograph has a loudness R. The Record Compartment control instead of the usual volume con- IS A sp The record itself is played in the trol, and it has a treble control instead middle of a sealed sound chamber rep- of a tone control. At every setting of the resented by the solid half -inch -thick loudness control, the tonal balance is w . 5 cabinet walls. Every available air space automatically changed to give optimum 4,1 within this enclosure has been utilized reproduction for that given sound level. The treble control influences only the __...... to create the desired sound and the air 0 pressure produced by the speakers has very high frequencies; for instance, the 10 1.5 t.o 2.5 to be preserved during playing by keep- difference in output for the maximum VOLTS RMS ACROSS LOAD ing the lid closed. If, while playing rec- and minimum treble positions is 12 db at 10,000 cps, but only 3 db at 3,000 cps. ords, one were to lift the top even a Fig. 6. Intermodulation distortion vs. power trifle, the bass would disappear almost The circuit schematic is presented in output. completely. Fig. 4. The changer proper is a V -M three - The two six -inch loudspeakers are Performance speed type, floating on springs within identical and have a resonance frequency It may be of interest to explain how the sound chamber in such a way that of between 85 and 90 cps. Nevertheless, the sound pressure curves of Fig. 5. there is no acoustic feedback between the over -all sound pressure output of were taken. Instead of placing the the pickup and the loudspeakers. The the system is quite adequate below the phonograph in a sound test chamber arm and cartridge have been specially speaker resonance frequency. and carrying out measurements the conventional way, the player was set up in 7500 (TONE) a room, the acoustic properties of which

01 v2 approached home listening conditions. 351.6 T O A large number of sound pressure curves were derived using different dis- i 6. [Contin-ued on page 59] fI PP 35L6 H. P. 0.22MEG 18 ICI 200C 12AxT 01 OBSERVE 35Z5 0.1 PHASING (SEE NOTE) 0.501 SPEAKER LOAD 0.10000.4 SPEAKER V1 V2 V3 Vt v31 LOAD t T 7 Vt 331.6 POLARIZE PLUG FOR 352 II MUM lul 600 10W

24 1W 1002W 10000

13 2.0 2.5 VOLTS RBIS ACROSS 117 40,150V TOPL5OV T0,150V LOAD Goti A 4001 SPEAKER OS,400V LOAD a4001 RESISTOR LOAD 1.6 DRYS TRIBE LOCATION

e NOTE REVERSE PHASING OF SPEAKERS WILL ELECTRICAL GROUND CAUSE LOSS OF BASS.

REVERSE PHASING OF FEEDBACK WILL 1s Lo 23 C11AS515 GROUND CAUSE AMPLIFIER TO OSCILLATE. VOLTS RMS ACROSS LOAD BACK OF CABINET CUTOUT

Fig. 4. Over -all schematic of the "360." Fig. 7. Harmonic distortion vs. power output.

AUDIO ENGINEERING MARCH, 1953 29

www.americanradiohistory.com Theater Sound in a Small Package

THOMAS R. HUGHES

Part 2. Continuing the description of a speaker enclosure which is claimed by the designer to be superior to any other type with which he has had experience. Constructional details are given in this installment.

IN THE PRECEDING ARTICLE, the writer capacitors in the dividing network, the discussed the many practical and voice-coil impedance should be around technical reasons why he believes 16 ohms at 400 cps. This isn't critical, this system to be the only completely however; a value of 8 ohms is still satisfactory means of properly reproduc- usable. ing classical music in the average -size The most critical item is the sus- living room, and this installment is de- pension of this cone. It will have a much voted to the construction. The first as- greater excursion than any normal sembly is illustrated at various stages 8 -in. speaker, so both the center spider during the building, but the views shown and outer surrounding ring should be are just suggestions. The dimensions of some plasticized cloth fabric or soft and proportions can be varied to fit the leather rather than the usual molded mat particular speaker and other materials of paper. These suspensions must be at hand. free in movement (not stiff) but able The first woofer had such a large to stand the punishment of the greater field coil that the cabinet had to have Fig. 4. Detail of the speaker mounting ring to flexing. The effective working diameter considerable depth from the front, or be attached to the horn of Fig. 3. of the cone proper-its outside diameter face, back into the corner of the room. -will probably be around 6 in. This meant that the face was wider Suitable speaker frames -including also; as you can see, the base of an the magnet structure-can usually be The Intermediate Horn equilateral triangle increases with the obtained for a relatively low cost from Bolted to the mounting ring of the altitude. The second assembly was built a shop which specializes in reconing 8 -in. woofer is the direct- radiating in- around a woofer with a permanent mag- speakers. While many of the modern termediate horn. Through this horn net and was scaled down somewhat in high -flux- density speakers would pro- passes the major portion of the funda- dimensions because the smaller magnet vide an ideal magnet for this purpose, mental notes and the drum and cymbal could be fitted into the corner more it would be futile to suggest disassem- crashes, etc. For the low notes of the snugly. bling one of them for the special type outside horn, the shape of the walls is The woofer may be built up by re- of woofer we desire. It was stated pre- not so important but for this inter- moving the frame from the permanent viously that such speakers were rela- mediate horn we must carry the flare magnet structure of an old 12- or 15 -in. tively expensive, and that this design out in a smooth exponential curve. spealrer and replacing it with a sturdy was economical. To meet all requirements, a throat 8-in. frame. However, a high -quality Having secured a suitable magnet opening of 4% in. square works out field-coil magnet can be used, if avail- structure, it might also be possible to best. Take a sheet of paper and draw an able, provided it has adequate wattage obtain from the same source a frame axis across the center. Then plot "basket" points so as to provide a large magnetic flux - or for an 8 -in. speaker. Re- on it starting with the 4 % -in. throat, somewhere around 10,000 lines per sq. member that this basket should be as so that you will have a side elevation of cm. It is necessary that the structure deep as possible -the one used on some the horn standing on its mouth, as in selected have a deep voice -coil slot, and of the earliest dynamic speakers is the Fig. 3. Measure off three divisions of that the pole pieces are long axially. type to obtain. Assuming that you suc- 1% in. each along the axis and strike The voice -coil diameter should be at ceed in obtaining a permanent magnet off a chord at each division, perpendicu- least 1% in., and 1% in. or more would unit, be sure to cover the voice -coil lar to the axis. The area of the throat be even better. opening immediately with Scotch tape - opening is 20.25 sq. in. By doubling this either the cellophane type or that known area and extracting the square root, it 3721 Hillcrest Dr., Los Angeles 16, as masking tape -to preclude the slot is found that the span along the side Calif. being filled up with metal particles. Once at the first chord will be 6 -1/3 in. Plot these particles become lodged in the voice -coil slot, it is almost impossible to remove them- although one of the most effective ways to "try" to get them out is to fold a piece of this same tape over the end of a thin strip of metal, which can then be used to "wipe" the slot. A large percentage of the filings can be removed in this manner, although some are almost certain to remain. After you have mounted the smaller frame on the magnet the rest is up to the speaker reconing expert. He must design a steep cone of stiff parchment, such as phenolic impregnated paper, and a voice coil to handle the wattage re- Fig. 3. Detail of one side of the metal horn quired for a small woofer. To match the Fig. 5. Detail of the mounting of the speaker covering the range from 450 to 1000 cps. average horn tweeter and utilize smaller on the flange and horn.

30 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com ga. or heavier. Cut out a circular piece the same diameter as the outside edge of the 8 in. speaker frame. Scribe a circle on it which will just clear the inner edge of the speaker gasket where it bolts on to this flange. Then mark off the 4% x 4%-in. square in the center of this circle and saw across the di- agonals with a hacksaw, as shown. Drill two rows of A-in. holes at the corners for starting a saw blade in the cuts. Clamp the circular edge in a vise so Fig. 6. Completed horn, shown with the early that a 4 % -in. side of the square is flush electrodynamic driver unit used in the first with the edges of the vise jaws. If the Fig. 9. Method of mounting horns to front of model. vise does not have jaws wide enough, cabinet structure. the width can be extended by two small half of this distance along the chord to pieces of angle iron. Bend the triangu- allow the soldering iron point to apply each side of the axis. At the next chord lar piece, between two diagonal saw heat effectively and to flow the solder the dimension will be 9 in. and at the cuts, inward to a 90 -deg. angle against between mating edges. After you are mouth it will be 12A in. the vise jaw. Then trim off the triangle sure every thing fits properly, these re- Next, trace a smooth curve through to leave a % -in. lip as shown. Bend maining two sides may be riveted to the the four points plotted on each side of over the next triangle, being careful to flange at the speaker end. Some me- the axis. This is best done with a choose the side that will let the tin snips chanics like to tin the mating surfaces "French Curve;" you may not find a clear the first lip just cut. Continue before assembling. Use a little "cut" curve that falls exactly on all four around for all four triangular seg- muriatic acid on the edges and solder points but retrace the different sectors ments so that a 4% x 4 % -in. mouth with half -and -half solder and a large to get it as close as possible. Then use opening with % :in. lips results. soldering iron. Solder an inch or two a flexible rule to measure the length of The lip extensions, at the throat line at a time while clamping the edges in this curve to determine how long to cut of the horn sides, should be cut to match snug position with "C" clamps or other the sheet metal side from throat to the portion of the flange they mate with, suitable means. mouth. around the mouth. These lip pieces may After all corners are well soldered, To make these sides, get some 22 or be bent over at approximately 90 deg. place the throat opening over a flat 24 ga. furniture steel. 20 ga. is a little and the extensions on the bottoms of two extension of the vise or an anvil and stiff for shaping but would give greater sides may be bent over in the same di- use a hammer lightly to shape the inner rigidity of the horn walls. On the steel, rection, to an angle of approximately %-in. lip back against the inner surface draw the axis again and then lay off 45 deg. Then the two sides without ser- of the horn for soldering. For riveting the distance along the axis that was rated edges may be clamped against the in tight places or for this shaping pro- measured around the curve. Divide this flange, facing each other, with the % -in. cedure, a stiff bar or angle iron can distance into three equal divisions for lip of the throat extending inside the be clamped to extend out from a strong the chords and lay off the former dis- horn and their upper lip pieces against vise. This lip should be soldered to the tances across the chords for the points the flange on the side away from the horn wall to kill any chance for spurious of the curves. speaker gasket, as in Fig. 5. vibration between the horn and flange The curves will be the same for all While these pieces are clamped along sections. Figure 6 shows the finished ap- four sides of the horn, but two of the the edges, drill small holes and rivet pearance. sides must have a / -in. strip added small tinner's rivets or nail stubs, so When you are through soldering there along the edge as shown in Fig. 3. At that they fall within the circle you drew must be no visible air leaks up the cor- the mouth of these two sides leave an to clear the speaker gasket. After rivet- ners of the horn or where the flange is extension of an additional 1 in. to bend ing the two sides on, they can be care- attached. The speaker mounting ring over. At the throat of all four sides, fully shaped over a large pipe or other must have a continuous gasket to mate leave an extended lip as shown. Cut out cylindrical surface, for the horn flare with this horn flange, for completing the two pairs of sides as drawn, and curvature. Next, form the horn flare in this air -tight effect. Before the speaker then snip out little wedge -shaped pieces the two remaining sides and then bend is bolted to the horn, solder a piece of from the % -in. extended edge left along over the saw -teeth edges to the proper light hardware cloth across the throat the curves of two of the sides. angle with pliers. of the horn flange, leaving no free edges The flange shown in Fig. 4 must be These saw -teeth are to reach along to vibrate. made from furniture steel of at least 20 the outside of the other two sides and [Continued on pn,7e 64]

SECTION T -T SECTION ItY

Fig. 7 (left). Horizontal and vertical sections through the center of the speAer unit for the second model, using a PM dynamic driver. Fig. 8 (right). Sections through first model, using the driver shown in Fig. 6.

AUDIO ENGINEERING MARCH, 1953 31

www.americanradiohistory.com Handbook of Sound Reproduction

EDGAR M. VILLCHUR

A discussion of the basic structure of one of the most important elements of a sound system, with an analysis of the effect of constructional features on its performance.

Chapter 1 0 . Loudspeakers. ( Part 1 )

LOUDSPEAKERS are electro- acoustic de- the diaphragm of a horn -type speaker, vices for converting the electrical SPEAKER FRAIE makes immediate contact with the air output of audio amplifiers into me- IRON STRUCTURE RIM SUSPENSION into which it radiates sound. chanical COMPLETING MAGNETIC PATN and then acoustical energy. CONE Modern loudspeakers The Mechanical System Speaker are almost ex- CENTERING DISC of the clusively of the (SPIDER) dynamic (moving -coil) If the cone and voice coil were mass- type. DUST COVER The dynamic loudspeaker allows less and perfectly rigid, and there were the electrical signal to pass through a PERMANENT perfect freedom of motion for the voice coil which MAGNET POLE PIECE is free to move along its coil, an analysis of cone vibrations longitudinal axis, and which is sus- SLUG VOICE COIL would only need to be concerned with pended in a transverse, fixed magnetic the electrical and magnetic character- field. Since the coil is made of non- MAGNETIC GAP - PIGTAIL LEADS istics of the speaker "motor ". Unfor- magnetic material the static field TO exerts VOICE COIL. tunately for speaker fidelity, however, no force on it except when current the mass, flows. elasticity, and friction of the An electrical signal changing in mechanical system of moving parts the same complex way as the original have a strong influence on motion of the sound pressur' will set up imitative Fig. 10 -1. Typical single -cone, single- roice- cone. When the voice coil is forced vibrations, anti the moving `voice" coil coil, direct- radiator speaker. into vibration the inertia of the moving is given a bite of the air by an attached cone or diaphragm. The efficiency of the conversion from mechanical to acoustical energy is Increased by means of some type of acoustical coupler between 1 COAMLIANCE, RM SUSPENSION the speaker and room, such as a horn FRICTION, RIM SUSPENSION or baffle. It may be seen that the first step of COMPLIANCE, SPIDER the above conversion, from electrical to Fig. 10 -2. Mechani MAGNETO - cal system of a dy- MOTIVE FORCE mechanical energy, is exactly analogous FRICTION, SPIDER to the action of an electric motor, where namic loudspeaker (ignoring load ) current is passed through an armature air and electrical anal ASS, VOICE COIL 0 free to rotate in a fixed magnetic field. ogy. Figure 9 -1 illustrates a typical direct- radiator loudspeaker, so called be- ASS, CONE cause of the fact that the cone, unlike

Contributing Editor, AUDIO ENGINEER- ING.

mass and the springiness of the spider and rim suspension create forces of Ì AIR LOAD RESISTANCE - their own. The speaker mechanical _1, system is a resonant source of sound in addition to an imitative one, and . ,,,,eal when stimulated it tends to oscillate at i.,- AM LOAD MASS RE ISTANOE- its own natural frequency independently Fig. 10 -3. Air -load of the controlling signal, especially when impedance per unit the stimulus is at a frequency at or near IIwIIr area of cone in in- resonance. Behavior at other frequen- finite baffle. After cies follows the laws of resonant á Iry Olson. systems unwillingly forced into un- natural vibration.

Speaker Dynamical Analogies I Dynamical analogies relating mechani- mmo cal. acoustic and electrical phenomena I FREOUENCY IN CYCLES PER SECOND prove helpful in the understanding and design of speakers. Many articles on elec-

32 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com If the system is subjected to vibration this goal. at frequencies below resonance the Below resonance, the output of the inertial effect of the moving mass will be speaker falls off as sharply as we would relatively small, and the predominant expect it to unless special mounting influence on motion will be the stiffness devices are used. Above resonance, cone of the elastic suspension, or, to put it velocity also decreases with increase another way, the system will be com- of frequency, but this effect is offset by the load resistance in- pliance controlled. the analogous the fact that air (In creases with frequency at about the electrical system the generator will see same rate. (See Fig. 9 -3.) It is the air a net capacitance.) Velocity will de- load resistance which determines how Fig. 9 -4. (A), Cone break -up at 450 cps (pho crease with frequency, in the same way much speaker mechanical energy will tograph taken by dusting lycopodium powde that alternating current through a ca- be absorbed by the acoustic load, and on the cone, which is shaken off by the ve pacitor decreases with frequency. so the acoustic output of the speaker is locity loops and retained by the nodes). (B) At resonance only friction must be kept fairly uniform, in spite of decreas- Cone break -up at 2700 cps. After Corrington overcome and the velocity of the cone ing velocity of motion, up to a fre- inductive the air load resistance tro- acoustic devices have appeared which will be at a maximum. Just as quency at which cannot be read intelligently without a and capacitive reactances balance each reaches its maximum and remains con- knowledge of electrical analogies. other out at resonance of the electrical stant. This frequency is reached when In order to draw the equivalent elec- circuit - leaving only resistance and al- the diameter of the speaker cone is trical circuit of the speaker mechanical lowing maximum current flow -the about two -thirds the wavelength of the system in Fig. 9 -2 we must recall the mass and compliance "mechanical re- signal. For a twelve -inch speaker the basic elements of our analogical system, actances" balance out. Thus the op- critical frequency would be in the neigh- which are here reviewed: posing inertial and restoring forces are borhood of 700 cps. Electrical Mechanical just equal. Above this point speaker output At frequencies above resonance the should start decreasing in inverse pro- Voltage Force frequency, an ad- Current Velocity system becomes mass controlled (the portion to the but Inductance Mass generator sees a net inductance). The ditional element mitigates and, in the Capacitance Compliance (reciprocal of effect of inertia increases with the more lower treble octaves, even overcompen- stiffness) rapid changes of velocity, while the sates the deficiency. At higher fre- Resistance Mechanical resistance impedance of the suspensions decreases. quencies the cone ceases to move rigidly (friction) (Inductive reactance increases, capaci- and "breaks up" into new modes of reactance decreases with fre- vibration, (see Fig. 9-4), so that the The mechanical system of a loud- tive speaker may thus be represented by the quency.) Velocity for the same applied mass of each individually vibrating electrical analogy of Fig. 9-2 (assuming force will therefore decrease as the fre- section is much less than the total mass. that the cone moves as a unit, and ignor- quency is raised, like current through an New, higher resonances come into play, ing the effect of the air load.) The two inductance, and force and velocity as- and standing waves are formed. One of inductances appear in series because both sume a reversed phase relationship. the purposes for which concentric cor- cone and voice coil add to the total mass, The behavior described above would rugations are often inserted in the cone while if the inductances had been shown seem to dictate very uneven reproduc- is to partly control this break -up, by in parallel the inductance of each would tion of the audible spectrum of sound creating high compliance at predeter- detract from the total inductance of the from base combination. The two capacitors must frequencies, with peak output at the mined points along the line also be shown in series (although the resonant frequency of the speaker's to apex. As in the case of other resonant suspension compliances seem to be in mechanical system. But there are certain modes of the speaker mechanical system, parallel mechanically) because the stiff- factors that work in favor of level break -up resonances cause transient ness of each of the elastic suspensions frequency response, and there are meas- response and linearity of output to detracts from the total compliance, just ures which may he taken to help achieve suffer, and peaks and dips are intro- as each capacitor reduces the total capacitance of the electrical system. An- other way of seeing the necessity for representing the two cone suspensions with a series electrical connection is to R. C. M.. My ® Mc, think of one of them as frozen. Cone ve- /.h. locity would then become zero, in the same way that opening one of the series capacitors would stop all current flow. ( "Frozen" implies infinite stiffness, and its reciprocal is zero compliance, which corresponds to zero, or open, capaci- fTR. tance.) The inductive and capacitive elements of the electrical system form a series resonant circuit, presenting minimum im- Fig. 9 -5. (A), Me- pedance at resonance, and the exchange chanical system of of energy between them follows the same a two -cone, single - laws as the energy exchange in the me- voice -coil speaker chanical system. and electrical anal- We may now examine the behavior ogy. (B), Variation of the loudspeaker mechanical system of (A). G. Mec M., ® Mc, when alternating magnetomotive forces to of various frequencies are applied ,2 the voice coil. The analogous electrical circuit will be referred to when it seems advantageous. Such references are only for the sake of clarification ; they are not essential to the explanation. For simplicity we will at first ignore the influence of the internal impedance of the amplifier source and the effect of the extra load on the cone imposed by the air.

AUDIO ENGINEERING MARCH, 1953 33

www.americanradiohistory.com duced into the frequency response curve. tended, and improving the air coupling Other methods to subdue the speak- has the dual benefits of effective damp- er's bid for a life of its own are: ing and increased efficiency. Since the B OHM (BLOCKED of load IMPEDANCE) 1. DAMPING. resistive component the acoustic impedance allows power to be perma- In an electrical resonant circuit the nently transferred to the medium, the Ç E SEEN BY VOICE COIL 1- B OHMS presence of resistance dissipates energy resistance reflected back into the speaker in heat. Instead of energy merely being cone is called radiation resistance. tossed back and forth between coil and Electrical damping by the amplifier, capacitor, a certain amount of power which will be discussed in detail in the is consumed by the system. The circuit chapter on power amplifier stages, is becomes broadly tuned and has its also very effective and does not create resonant peak reduced, a condition in efficiency loss. E which it is said to be damped. Z SEEN BY VOICE COIL S 16 OHMS In a mechanical resonant system the 2. DESIGN FOR Low RESONANT FRE- same results are produced by friction, QUENCY. which takes its toll of energy during The lower the resonant frequency of Fig. 9 -7. How back e.m.f. increases the effec- each exchange between inertia and re- a speaker the more 'extended its low - tive electrical voice -coil impedance seen by storing force. The violence of resonant frequency response, and the less annoy- the amplifier (source impedance neglected). oscillation for a given applied force, ing the resonant peak will be. In some and the time required for oscillations cases it is possible to keep speaker to die out, are decreased. Speakers are resonance below the main band of fre- 3. DISTRIBUTION OF MASS OF THE not, of course, purely mechanical sys- quencies being reproduced. Typical MOVING SYSTEM. tems, and they are damped in three values for commercial speakers twelve The principle of inserting cone cor- ways: internally, through mechanical inches and larger are from forty to rugations for controlling break -up may friction in the suspension system and eighty -five cps. Low -frequency reso- be followed through in a special design cone; acoustically, through the air load nance calls for higher compliance rela- which uses definite segregated vibration resistance; and electrically, through the tive to the mass, or high mass relative to systems in the cone and /or voice coil. source impedance of the amplifier, the compliance, but other design con- In Fig. 9 -5, (A) illustrates a speaker which acts as a shunt load to the electri- siderations must be taken into account of this design, in current commercial cal generator system of the voice coil before values of mass and compliance use, which has an aluminum dome - and magnetic field. can be decided upon. For a given mass shaped diaphragm for high- frequency Too much friction in the speaker the compliance must exert enough rela- At will obviously cause a se- sound propagation and dispersion. suspensions tively linear restoring force so that the suspended vere loss in efficiency, since the energy voice coil is not carried out of the area low frequencies the entire dissipated is entirely wasted. It is of uniform magnetic field, or does not mechanism vibrates as a unit, but at especially advantageous, however, to allow the voice coil to "bottom" against high frequencies the small cone and damp the rim suspension of the cone the flange of the pole piece. Another diaphragm are able to vibrate by them- mechanically. This suspension is the factor that must be considered is the selves because of their compliance with termination of the path, beginning at influence of a large mass in impeding the cone proper. the voice coil, that is followed by the reproduction of the higher frequencies, The reader will find that tracing the sound when the cone ceases to move as or of the transients of lower frequency equivalent electrical circuit of this a unit. If the rim is damped (internally tones. The air load again comes to our speaker system increases appreciation of or by an external application of viscous assistance in this matter. At low fre- the way it works. In (A) of Fig. 9-5, the material) in such a way that sound quencies the air load has a proportion- magnetomotive force must always over- waves reaching it encounter a minimum ately high "reactive" component, which come the friction of the spider R., the of impedance discontinuity, a good part is to say it adds mass to the speaker stiffness of the spider, determined by Ce, of the energy that has not been radiated system and lowers the resonant fre- the mass intertia of the voice coil Moc, can be dissipated in the mechanical re- quency. Although we normally expect and the inertia of the first section of cone At this point, sistance of the suspension, instead of a mass reactance to increase with and aluminum done Mci. being reflected back along the cone. frequency, the air load is peculiar. marked X on the diagram, there is a The formation of standing waves is thus Above a certain frequency (see Fig. choice of path. At low frequencies Cc will have a high impedance (will remain discouraged, while vibration of the cone 9 -3) the reactance decreases with fre- mechanically stiff) and Mc, a low im- in smaller masses can still place. the mass take quency, so that compared to will flow through Standing waves also damped by the of cone is pedance, so that current are reactance the and voice coil it Mcs rather than Co. The current through use of a soft, spongy cone frequencies. material. greatly reduced at higher Mcs will be the same as that through Mc Energy absorbed by the air load re- It is a case of having our cake and which represents the fact that the two sistance is being used precisely as in- eating it too. sections will have the same velocity and will move as one. As the frequency is raised the impedances of the two paths approach each other in value. At some particular point they will be equal, and half of the current will be by- passed through Cc, which Bo q means that half of the energy supplied will be used up in vibrating Mc. inde- lË pendently from M00. The compliance of óeo Cc relative to other components of the Fig. 9 -6. Electrical system is adjusted so that the impedances :. voice -coil impedance of the two parallel paths become equal of typical 8 -ohm at the desired frequency, called the cross- speaker. After F. over frequency. The system of mass and Langford Smith. gzo compliance which determines the fre- .../ quency of equal path impedance is sometimes referred to as a mechanical crossover network. At much higher frequencies Co as- sumes a very low value of impedance. Current is short circuited through it, 100 1000 Iaaao leaving little or IN CYCLESWPPER SECOND no energy for M00, (Continued on page 66)

34 AUDIO ENGINEERING MARCH, 1953

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www.americanradiohistory.com 1953 Radio Engineering Show GRAND CENTRAL PALACE, NEW YORK -MARCH 23 -26

Year's largest exposition of electronic equipment again takes to the boards for its annual four -day stay-in conjunction with IRE convention which offers literally hundreds of technical papers.

MARCH INVARIABLY BRINGS four days 0 0. 00 0. 0. 0 A Thursday afternoon session on Audio of sightseeing to the electronic en- will cover : "Sound Reinforcement System, o RADIO gineers, with its associated foot- -ELECTRONICS General Assembly, United Nations" by L. tiring walking past and into myriads of L. Beranek, "A Variable Time Delay" o A Preview of Progress °e by booths, each holding some equipment of in- Kenneth Goff, "A Flux- Sensitive Head for terest to everyone-some with displays of o I.R.E. CONVENTION Magnetic Recording Playback" by David exceptional interest 0 to those in audio. Al- 0000000000 0000 E. Wiegand, "Uniaxial Microphone" by though all branches of electronics are Harry F. Olson, John RADIO ENGINEERING SHOW Preston, and John represented, a relatively small number of C. Bleazey, and "Sound Pressure Measur- the exhibitors are concerned with audio, ment between 50 and 220 db" by J. K. so the IRE show does not compare to an Hilliard. Three sessions are devoted to Audio AUDIO Fair as an attraction to most of transistors, largely from a scientific view- JE's readers. However, since there is no ENGINEERING point rather than practical, and several Audio Fair in March, many audio people other papers will be of interest to the audio will be there. Booth 3 -316 engineer. The Radio Engineering Shows arè not Most of the audio exhibits are concen- open to the public at large, although there WALDORF- ASTORI A\MOTEL trated on the third floor of Grand Central is nothing to keep anyone away -except GRAND CENTRAL PALACE Palace, and are listed at the left of the the three -dollar admission charge, pos- NEW YORK CITY diagram below. Certain other exhibitors sibly. IRE members are admitted for one having considerable audio equipment are dollar, MARCH 23 -26 1953 and are also privileged to attend located elsewhere in the building, and are the technical,' sessions. paper.: -1.'im,I: n cnctl I í1,,,r . In l.. I.. listed at the right. As usual, 2E will be A new feature this year, seminars are Beranek, "Microphones" by Marry F. there, being located this year on the third being presented which will undoubtedly Olson, "Loudspeakers" by Hugh S. floor in Audio Center. Also on hand will be bring forth many interesting discussions. Knowles, "Phonograph Reproducers" by the 2nd Audio Anthology, as well as the Two sessions are being held on "Acoustics B. B. Bauer, "Tape Recording" by Marvin first one, along with current issues, infor- for the Radio Engineer" Wednesday morn- Camras, and "Studio Acoustics" by Hale mation about subscriptions, and anything ing and afternoon, with the following J. Sabine. else our readers are likely to ask.

AUDIO CENTER AUDIO EXHIBITORS EXHIBITORS r ON OTHER FLOORS 3 -317 Altec Lansing Corp. 4-405 Ampex Electric Co. Amplifiers, touera, loudspeakers Tape Ru' 'r'l. r. 3 -314 Amplifier Corp. of America 1-406 Arnold Engineering Co. Amplifiers, tape recorders Magnetic materials, cures 3.105 Audio Devices, Inc, 1 -112 Ballantine :Wdlodiscs, Laboratories Audiotape, Audio - Test Equipment points 2.128 Barker & Williamson 3.310 Audiocom, Inc. Audio lest equipment "High Fidelity" magazine 2-515 British Industries Corp. 3.3044 Solent Associates 4 Speakers, amplifiers, solder I'oncertone tape recorders t. 2 -106 Browning Laboratories, Inc, 3 -400 Fairchild Rec. Eqpt. Co. Radio tuners, AM, FM Phono pickups, tape and disc re- 11=- 2 -512 Cannon Eleehle Co. corders. and transcription turntables Plugs and connectors 1-801 Collins Radie Company 3.304A Fisher Radio Corp. Radio broadcast equipment Amplifiers, tuners, systems 1316 The Raven Company 3.309 Hytor Company h ..-.. Attenuators, test equipment Torok' coils. filters, etc. Sel 1 -109 Freed Transformer Co. 3.506 Jensen M an 'factoring Company Transformers. test equipment Loudspeakers 2-324 Gatos Radio Company 3-301 II ord, Inc. Radio broadcast equipment Magnecorder tape recorders 1-201 General Electric Company 3.506 The Motor Company r,.. Loudspeakers, pickups Loudspeakers, components 1.121 G I Radio Company 3.306 Presto Recording Corporation ,,, .. Laboratory and test equipment Tape and 7i disc recorders and Pr' Pr Jr' 1-402 Gray Manldaamino playback Company equipment Pickup arms, transcription 3.315 Raton Eleetrie eqpt. Co. 1 -509 Hewlett- Packard Loudspeakers, Co. horns Test equipment 3.316 Radio Mewing', Inc. -'a._--Jg-i --a. I 1-110 International AUDIO I...... i.-..1.e.j Resistance Co. ENGINEERING, the Resistors, potentiometers, Audio Anthologies etc. 2 -327 II easremenh Corporation 3.506 The Rola Company Laboratory and test equipment Loudspeakers, components 1.304 Radio Corp. America 3.112 Tech -Muta Products, it Inc. TV equipment, tubes Amplifiers. TV sets and kits 2-210 Shallcross Mfg. Company 3.311 University Loudspeakers, Inc. A ttemlateru, sultrhee. et e. Lmuul peakers, horns 4.801 Standard Transformer 3 -313 Waveforms, Company Inc. Truifnrmer, amplifier Amplifiers. test equipment hit, 2 -146 Tech Laboratories, Inc. 3-402 till-Davis Pohl !shine Co. Attenuators, sait ekes, "Radio etc. & Television Neues" 4-602 Triad Transformer Magazine Company Transformers. amplifier kits .w 4 -715 Tung -Sol Electric, Inc. J. Tubes -- -58ßl, 5657, etc. l 1-132 United Transformer Company VIEW 11.1. Transformers, amplifier kits

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www.americanradiohistory.com "First Inventor" Under the 1952 Patent Law

ALBERT WOODRUFF GRAY

The validity of a patent often hinges upon small and apparently insig- nificant points. Herein is clarified the current law regarding inventions which are described in a patent application, yet not claimed specifically.

APROVISION of the Patent Law that tion. The discovery, the court pointed withstanding the fact that he was ig- became effective last July is, "A out, had been substantially disclosed in norant of the pending applications person shall be entitled to a patent a patent application prior to the issu- which antedated his claimed date of in- unless . . . (e) the invention was de- ance of the action. vention and eventuated into patents, he scribed in a patent granted on an ap- "The discovery," asserted the Federal was not in fact the first inventor since plication for a patent by another, filed Court, "was merely the result of the his advance over the prior art, if any, in the United States before the inven- skill and knowledge of an electrical en- required only the exercise of the skill tion thereof by the applicant of the gineer." of the art." patent." When several years later the question The Senate Report on this bill before of the validity of this same patent came Disclosure in Claims vs. Specification its enactment states of this provision, again before the Federal Courts, the The decision in this case as well as that it is the inclusion in the patent patent was sustained by the United the enactment in the patent statute it- statute of, "Another well recognized States Circuit Court of Appeals and self of this distinction between the status condition imposed by a decision of the that decision appealed to the Supreme of an inventor who includes his dis- Supreme Court which was not expressed Court of the United States. covery in the claims made in his patent in the existing law ; for the purpose of "One of the problems of the art," said application and one who incidentally anticipating subsequent inventions a Justice Jackson in the opinion of the disclosed his discovery in his applica- patent disclosing the subject matter court, "has arisen from the variations of tion but failed to claim the discovery as speaks from the filing date of the ap- the received signals. When the set is a patentable invention, rests on a fa- plication disclosing the subject matter." tuned from a weak signal to a much mous case involving the first patent re- The former statute, now supplanted stronger one, the tendency is for poten- lating to oxy- acetylene torches for cut- by this new enactment, provided as a tial to build up in the last amplifying ting and welding metals. fourth defense to actions by a patentee tube, which results in what is known as Here the question was clearly pre- for infringement, "Fourth: that he was blasting in the loudspeaker. sented under the former patent statute, not the original and first inventor or dis- "Often the same signal varies in in- of whether the first and original in- coverer of any material or substantial tensity. Weakening may result in fading ventor could rest his right to a patent part of the thing patented." where the sound (re)production weak- on disclosures made by him in an ear- The former statute undoubtedly ap- ens or disappears; and strengthening lier application which were not included peared to its framers to express clearly may beget distortion of the sounds as claims, or whether he was restricted that a patentee had no grounds for an emitted. (The patentee) essayed to ob- to the claims he had set out. action for infringement of his patent if viate these objectionable features. It The inventors in this instance had he was not "the first and original in- was known that the amplification of the discovered the efficacy of a mixture of ventor." Unfortunately both for law- carrier signal could be controlled by in- oxygen and acetylene gases in the makers and for the people, no words creasing or decreasing the potential welding and cutting of metals. Patents nor group of words possess the clear-cut upon the grid of a triode amplifier. This were applied for and granted on the definition possessed by figures in mathe- patentee proposed to vary this potential implement or tool employed in the use matical equations. They are understood automatically so as to increase or de- of this combination of gases but not by the reader according to their mean- crease the degree of amplification and on the process or use of this combina- ing to him, but that is not always the thus hold it at a substantial predeter- tion of gases. understanding of their author. mined level. The court said of the circumstances Here this difficulty occurred in the "To this end he provided means to surrounding these applications, "It is interpretation by the courts of this ear- increase the negative potential upon the reasonably clear that the patentees at lier patent statute; was the original and anode of the detector tube in step with the time did not recognize the full value first inventor the patent applicant who the increased strength of the signal and of their invention, but the fact remains, first described the invention or the ap- to conduct a direct current from that whether they did or not, that they hap- plicant who first claimed the discovery anode to the grid electrode of one or pened upon a device which became the of the invention, when the discoverer more of the amplifying tubes. Thus an accepted form which has displaced all of the invention and the claimant were increase of the strength of the signal others and which seems likely to be the not the same? would automatically increase the nega- final tool by which metals will be cut The echo of this confusion in the defi- tive potential on the grid of the ampli- under this process." nition of "first and original inventor" fier and decrease the amplification; the When later the process that had been was heard in patent litigation involving reverse result would be effected if the disclosed in these earlier patent appli- a radio patent issued in 1932 for an in- signal weakened." cations, for which no patent claim had vention controlling volume in radio re- This description the Supreme Court been made, became the subject of a later ceiving sets. When suit was brought for supplemented with its conclusion that patent by others, an action for infringe- infringement by an assignee of this pat- the patent was invalid. "We conclude ment was brought by the original patent a few years after its issuance, the that this patentee accomplished an old entees. discoverer failed to succeed in his ac- result by a combination of means which The Federal District Court held that singly or in a similar combination were the discoverer had no claim as an in- +35 -36 76th St., Jackson Heights, N. Y. disclosed by the prior art and that, not- (Continued on page 58)

40 AUDIO ENGINEERING MARCH, 1953

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www.americanradiohistory.com Audio Fair -Los Angeles Rated Huge Success

Record attendance exceeds New York Fair records by nearly 50 percent -justifying Californians' claim to great interest in audio in that locality.

SURPASSING the expectations of nearly everyone in the industry -with the possible exception of those who were responsible for the show itself-the first Audio Fair in Los Angeles drew an attendance of 17,000 registered visitors, with an estimated 3000 more who did not register. Compared with the attendance at the 1952 Audio Fair in New York, this is somewhat of a record. With more than 150 manufacturers represented by approximately 75 exhibitors, the Fair offered everything from wireless microphones of broadcast quality, to three - dimensional tape -recorded sound -the latter being remembered as the hit of the last two New York shows. The Fair Directory included a page for Left to right: "Cap" Kierulff, publicity director of the Fair; Boyd McKnight, chairman of the comments from those who heard the stere- Advisory Committee and former Section Chairman; and Richard Hastings, Los Angeles Section ophonic demonstrations held on the main Chairman of the Audio Engineering Society. floor of the Hotel, and such comments as rulff, who topped off his two -month cam - Two papers of speecial interest at this these noted by the enthusiastic listen- were pa fps of advertising, press releases, and meeting were those on stereophonic re- ers: "Very life -like near to the actual -as radio announcements with a live telecast cording-one by Ross H. Snyder on "His- performance as I have heard to date -will on the eve of the show over KTLA. On tory and Development of Stereophonic do more for audio depth and the audio biz this TV announcement appeared several of Sound Recording," and the other on "Prac- than hi fi by itself -extremely realistic - the exhibitors, Fair Manager William L. tical Binaural Recording Systems," by sound magic home enjoyment will be -for Cara, as well as Mr. Kierulff. Otto C. Bixler and C. G. Barker. All as- more than worth whatever the cost may be pects of audio engineering were covered little too loud for the room and the AES Technical Sessions -a by the convention papers, which will be audience-how will it be made available In addition to the exhibits, the Los An- published in the Journal of the Audio En- for the public loud in spots but I still geles Section of the Audio Engineering -too gineering Society. The first issue of the enjoyed it LOUD Just Society-sponsors of the staged an -TOO (but OK)." Fair- Journal will cover the New York conven- a sampling of a few of the comments, but impressive list of papers for the first two tion in 1952, and will be ready in a few more importantly the indication of how days of the convention. Credit for the weeks. The second issue will contain the much interest there is in audio among the nineteen papers given goes to the hard papers of the Los Angeles convention, and general public they are introduced to work of the Section Chairman Richard -once will be in the late real high -quality reproduction. Hastings, Papers Committee Chairman published spring. The Journal of the AES is a new activity of On the back of the sheet which provided Robert Hopkin, Advisory Committee the Society and is headed by Lewis S. space for comments was a questionnaire Chairman Boyd McKnight, and the Chair- Goodfriend, Editor, and Jerry B. Minter, regarding where the visitor had heard of man for the Technical Sessions Allan Chairman of the Publications Committee. the Audio Fair the surprising result Wolff. In all, 19 papers were presented in -and Members will receive the Journal without was that the majority of them had learned the four sessions, covering Aircraft com- extra cost, and non -members may obtain of it by radio, with newspapers rating a munications and recording -motor systems, copies at a nominal charge. close second, and TV third. And for this Audio components and measurements, Au- attendance, the Audio Fair -Los Angeles dio amplifiers and equipment, and Record- could thank publicity director "Cap" Kie- ing. The Exhibit Site Despite the difficult parking conditions in the vicinity of the Alexandria Hotel in Los Angeles, and despite the inadequate elevator service during the heaviest rush hours of the three -day show, the rooms and corridors are admirably suited for the demonstration of audio equipment. The William L. Cara, Fair Manager, be- ceilings are high, and the rooms relatively fore KTLA's TV large, so that the chance of claustrophobia cameras on the eve was minimized. The wide corridors and of the show, pre- the H -like arrangement of the hotel per- pares to introduce mitted relatively free movement of the Maximilian Weil, of visitors so that the show did not appear to Audok, in successful be as crowded as the corridors of Hotel bid for attendance. New Yorker in the original Audio Fair location. But taken from all its aspects, the Fair and the Convention may be called a huge success, and those who had a hand in this success are well deserving of a standing vote of appreciation.

42 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com ALWAYS IN STOCK AT ALLIE D

get immediate SOUND WORKSHOP'S delivery on this new CUSTOM 800 COMPLETE SYSTEM An outstanding FM -AM Radio -Phono combino- tion that excels standard type consoles selling at deluxe equipment higher prices. Supplied complete -ready for operation. High -fidelity components include: Pilot FM- AM AF 821 Tuner; Webster- Chicago 3 -Speed Changer; Jensen H -222 12" Coaxial Speaker; Grommes 100 BA 10 -Watt Amplifier; G. E. Triple - Play Variable Reluctance Cartridge. Beautifully housed in outstanding modern cabinet, with acoustically designed speaker enclosure. Size: 53" w, 32 '/2" h, 18" d. Shpg. wt., 110 lbs. FISHER AUDIO COMPONENTS 98 -641. Cordovan Mahogany. 98 -642. Blonde. Model 50 -A Lab Standard Amplifier. Deluxe all. Either Model, Net $391.50 triode amplifier of the utmost fidelity. Response: ± 0.5 db, 15- 60,000 cps at 40 watts. Harmonic distortion: ALTEC SPEAKERS .05% at 5 watts, .08% at 10 watts, 0.3% at 40 watts. Intermodulation: 0.4% at 10 watts, 0.8% at 40 watts. 820A Corner Speaker System. Altec's finest Hum: better than 92 db below full output. Output im- speaker installation. Response exceptionally Bat from 50- 16,000 cps; 30 watts power rating; cross- pedance: 8, 16 ohms. Chassis sire: 8 x 141 x 9" high. over 800 cps; output matching imp. from 6 -12 Complete with tubes. For 105.125 v., 50-60 cycles AC. ohms. System consists of: 821 mahogany corner Shpg. wt., 45 lbs. cabinet; 802B high frequency unit with H -808 98 -628. Net $159.50 multicellular horn, two 803A 15" low frequency speakers and N -800D dividing network. Cabinet Model 50 -C Master Control. For Audio use with 47%" h, 421/4" w, 29" d. Shpg. wt., 230 lbs. amplifier above o any other quality amplifier. Inputs: 95-048. Net $525.00 3 -for TV tuner, r radio tuner, tape playback; 1-all magnetic cartridges; 1- high -imp. make. Outputs: 1- 604C 15" Coaxial Speaker. Flat response from for amplifier; 1 -for recorder. Response: ± 1 db, 20- 30- 20,000 cps. Has 15" cone for low frequencies; 20,000 cps. Harmonic distortion: .05 :b at 5 v., 0.4% 6 -cell high -frequency tweeter coaxially mounted at 15 v. Intermod: 0.2% at 5 v., 1.6% at 15 v. In ma- for 60° hor., 40° vert. distribution. With N -1600A hogany cabinet, 151/4 x 41/2 e 61/2' deep. With tubes. crossover network. Ratings: 50 watts peak, 35 For 105 -125 v., 50 -60 cycles AC. Shpg. wt., 9 lbs. watts continuous. Voice coil imp., 16 ohms. Depth, 11 '/s ". Shpg. wt., 57 lbs. 98-626. Net $97.50 95 -057. Net $156.00

602A 15" Duplex Speaker. 30- 20,000 cps ELECTRO -VOICE 4 -WAY SPEAKER SYSTEM response. Has 15" bass cone and coaxially- mounted tweeter. With N -3000A dividing net- The Patrician. Features Klipsch type "K" indirect - work. Sectionalized horn with 2 x 3 aspect ratio design for radiator truly magnificent sound realism. for smooth distribution. Power rating, 20 watts. Perfectly matched components include: 18WK 18" Shpg. wt., 25 lbs. L -F driver (16 -200 cps): 12W -1 L -F driver (200 -600 95 -084. Net $114.00 cps); T -25 treble driver (600-3500 cps) exhausting through 6 -2X5 cellular horn; SP8 BT 8" super- tweeter augmenting T -10 HE driver to full- powered 16,000 BROOK 12A4 AMPLIFIER cps; X -26' ' -1 4 -way crossover (200, 600, 3500 Consists of Model 12A basic amplifier cps). House in distinguished custom corner cabinet. and Model 4A preamp. Response: j All components installed and wired. 60" h, 41" w, 0.5 db, 20- 30,000 cps at 10 watts. Hor- 30" d. Shpg. wt., 500 lbs. monic distortion: 1.21 % at 10 watts. 81 -413. Mahogany. 81 -414, Karina Blonde. IM: 2.56% at 10 watts. Output imp.: Net, either model $712.95 2, 4. 8, 16, 500 ohms. Amplifier size, 17 e 61/4 x 81/2 ". Complete with tubes Shpg. wt., 28 lbs. 98 -701. Net $222.00 CRAFTSMEN 800 FM -AM TUNER The famous tuner with the outstanding features: Model 4A Preamp Only Features new 9- position wider AM bandwidth; sharper IF bandpass "skirts "; record compensator and built -in preamp with front -panel selected equaliza- loudness control. Requires power supply tion for recordings; AFC; magic -eye" tuning; when used with amplifier other than Brook 12A. Complete with tubes. Shpg. tuned RF on AM and FM; separate triode conver- wt., 10 lbs. ters; output, 2 v, less at than 5% distortion; output 98 -702. Net $109.50 matches high- or low -gain amplifiers with input imp. of 10,000 ohms or higher; input for TV, recorders, etc.; dual tone controls. Chrome -plated chassis, GARRARD RC -80 CHANGER 1 31/4 e 101 x 7 ". Complete with tubes and cables. Plays all speeds (331/2, 45, 78 rpm) and all sizes (7 ", 10 ", For 105 -125 v., 50 -60 cycle AC. Shpg. wt., 17 lbs 12 ") automatically. Changes 45 rpm records on special 98-002. Net 5159.50 spindle -no adapters required. Shuts off automatically after last record is played. With 2 plug -in heads and hardware fo- G. E., Pickering or Clarkston cartridges. Less cartridges and preamp. Shpg. wt., 18 lbs. FREE 1953 CATALOG 96 -422. Net .... 541.45

Write today for our complete 236.Page Buying Guide listing the world's largest ALLIED RADIO CORP., Dept. ,17 -C -3 selection of High -Fidelity systems, 833 W. Jackson Plvd., Chicago 7, Illinois amplifiers, tuners, speakers, changers Send FREE 1953 rsLLIED Catalog. and accessories -available for immediate shipment from stock. If it's anything in Ship the following ecuipmentt Hi -Fi, you'll find it in your ALLIED Nome Cornlog. Send for it today. Address....

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AUDIO ENGINEERING MARCH. 1953 43

www.americanradiohistory.com C`.111III. r. PHONO POSIT ION mInmIsip Equipment Report E PRE AMP "IN, ' . UIII , .1.11111.10.1.1.aoll \UIII= PILOTONE AA -901 Amplifier and AF -821A PILOTUNER 111111---- PHONO THE PILOrotiE AA -901 amplifier employs 10 watts the distortion remains below 0.4 : aT'-' 111 o 1 AND TV the conventional Williamson circuit, per cent. .ia%ISiliiì.111I11 with a number of desirable features. The amplifier chassis is provided with a t!Ìi17rlIït111111 Means are provided for adjustment of bias power switch, pilot light, and two con- on the output stage, as well as for balance venience outlets for other equipment. Fig- 111111 between the two tubes. By connecting a ure 2 shows some unusual features in the voltmeter between a two- terminal strip power supply section of the amplifier. and ground, output cathode voltage may be The AF -821 Pilotuner consists of a read, and a control permits adjustment of combination AM-FM tuner, tone and vol- this voltage to suit the tubes. With KT -66's ume controls, and a phono preamplifier PILOTONE -normal equipment in the amplifier -40 which may be switched in or out at will, I:a AA J01 volts is recommended; if the user wishes thus making it possible to change from

II to change to 5881's, the correct bias is 38 crystal to magnetic pickups with a mini- &i volts. By removing the jumper from the mum of effort. A jack is provided for TV terminal strip and connecting the meter be- sound input, and the selector switch per- tween the two terminals, the plate currents mits selection of the desired source signal. of the two output tubes may be balanced The built-in antenna connection for FM by turning another control to obtain a appears to provide good signal pickup, zero indcation on the meter. even up to 40 miles from transmitter loca- es r r - Howe. oaTr~i1T-.rTS Rated output is obtained with an input tions ; the AM pickup on the iron -cored voltage of 1.0, which corresponds to a antenna coil is sufficient for most installa- Fig. 1. Measured performance data for the 025 -volt input for the standard measure- tions. Pilotone AA -901 amplifier and the AF -821 ment output of 1 watt. IM distortion at the While tone control curves seem to be Pilotuner. 15 -watt output is 2 per cent, while up to less severe than many others, they would undoubtedly be adequate for normal instal- raw. MAO. lations. The phono preamp has a fixed equalization curve which matches LP rec- A65N 701 %6SN7GT A65N7GT 1( T 66 ords quite closely, and tone controls permit minor trimming of the response curve. The circuit employed in the phono preamp is simple and effective, and might well be studied as an example of good commercial engineering. A detector output is provided to feed a signal to a tape recorder without being affected by the volume control, or to an amplifier which was equipped with tone and volume or loudness controls of its own. Two convenience outlets on the tuner chassis can be used to accommodate the power amplifier and a turntable, and both are controlled by the on -off switch. The selector switch also controls dial lights-il- luminating the one in use-or operates pilot lamps for the phono and TV positions.

Fig. 2 (left). Schematic of the Pilotone amplifier. Fig. 3 (below). Schematic of the AF -821 Pilotuner.

61146 . MN ,... ° .... Ont. w. :.a.6 .---__ _ - rúi awl mina F

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44 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com HARVEY the House of Audio

The ORIGINAL The NEW WILLIAMSON HR -15 MINIFON Amplifier Kit Miniature, Portable

The famous. original WIRE Williamson HRl5 . RECORDER still acclaimed the leader ... in kit form, with the Partridge Out- Measuring only 1% x 4% x 6 %, and weighing only 2 lbs. put Transformer specified by Williamson in his original design. Assemble 7 ozs., the Minifon is just about the world's smallest sound this kit, and in 3 hours or less, enjoy the finest sound you ever heard. Operates from a tuner, phonopreamp, crystal pick up, or other signal recording instrument. Records, rewinds, erases, and ploys bock source. Absolute gain is 70.8 db with 20 db of feedback. Frequency through either a pair of stethoscope type earphones or an response: -.5 db, from 10 to 100,000 cps. Output impedances to match external amplifier. Capacity 21/2 hours uninterrupted recording. all speakers from 1.7 to 109 ohms. Kit is complete with 5 tubes: 1.5V4, Powered 11/2 v. 2.6SN7, and 2.5881 (or 807 if requested), 2- Punched Chassis, 2- Resistor by A battery, standard 30 v. B battery, and 7 Mounting Strips, Sockets, Partridge WWFB Output Transformer, Assembly Mallory RM -4Z mercury batteries. An ideal tool for executives, Instructions, and All Other Necessary Parts for Amplifier and Power engineers, doctors, and wherever there is need for recording Supply _. ... _. __...._ _._.. S76.50 notes, interviews, and other data. PARTRIDGE OUTPUT TRANSFORMER WWFB - Available Complete with microphone, stethoscope type earphones, Separately __ $26.50 1 hour spool of wire, tubes, batteries, end instructions. $289.50 HR -1ST as Williamson Kit - Furnished above, with TRIAD Morocco Leather Zipper Case 510.00 Transformers and Chokes $69.50 Transformer -rectifier Unit for operation of motor from NOTE: HR -IS and HR -1ST Kits may be hod with 117 v. AC line $20.00 British KT -66 Output tubes for $3.00 additional. RECORDING WIRE On spools, in dust -proof plastic containers, suitable for mailing.

The NEW V, hour $5.00 1 hour $9.00 hour 7.00 2 hour 17.90 McINTOSH 2'., hour 21.50 LOUDSPEAKER SYSTEM AUDAX POLYPHASE REPRODUCERS

Housed in an attractive enclosure for either flat -wall or corner One unit with two replaceable styli operating location. Provides a response ± 3 db. from 40 to 10,000 with one pressure (81/2 for all three record ( -- cycles/sec., and a useful response from 30 to 20,000 cycles /sec. grams) speeds: 331/3, 45, and 78 rpm. Provides ',,,. Four 12" speakers are used for low frequencies, an 8" speaker excellent for the mid range and four tweeters for high frequencies. coupling between stylus and record groove, with Nearly 4 square feet of diaphragm area ore thus provided high stylus compliance and minimum mass. Response is from 20 to for more efficient acoustical coupling, more closely approaching over 10,000 cps., with an output of about 20 millivolts. Needle -talk linearity in excursions, thereby reducing low frequency distor- practically nil. tion to a minimum. Over-all width of the enclosure is 43 inches, and the height is 30 inches. Front width is 221/2 inches. Power DL -6 Chromatic Head with Microgroove Rating: 50 watts continuous operation. Impedance: 8 ohms. Diamond and Standard Sapphire $41.70 L 20.70 Model F100 (blond finish) $374.50 -6 Head with two Sapphire Styli KL -4 Head with Sapphire Styli 20.70 Model F100A (Mahogany finish) 374.50 (for record changers)

CARTER SUPER CONVERTORS SPEAKER Deliver clean 60 cycle AC power at 115 volts. Operate from storage batteries or other DC R-J ENCLOSURES source, and available for 6, 12, 24, 28, 32, 64, or 115v input voltages. Ideal for on- FLOOR MODELS location recordings with quality equipment. Write for complete data and prices. Designed for use with ANY 12 or 15 inch speaker, this new sensation in high fidelity has no counterpart in anything CANNON PLUGS and CONNECTORS available today. The R -J is a new con- The standard of quality for over 15 years, You'll cept. Large enough only to accommodate find them wherever the ultimate is required in low the speaker, it reproduces tones to the lowest limits of audibility, level sound transmission, and general electrical and without hangover. The R -J is the amazing solution electronic 'applications. Write for complete data cleanly and and prices. to the problem of space versus quality. Model FM (Mahogany) 349.95 COMPLETE STOCKS CARRIED AT ALL TIMES FOR IMMEDIATE DELIVERY Model FB (Blonde) 54.50 Model F15UM (Unfinished Mahogany) 15" only... 43.35 HARVEY is the HOUSE of AUDIO Specify for 12 or 15 inch speaker.

Whatever it is in the field of Audio, you can be sure to find it at Harvey in stock, and ready for immediate delivery wherever you may be. Your inquiries are invited. NOTE: Prices Net, F.O.B., N.Y.C. HARUEY RADIO COMPANY, INC. Subject to change without notice. 103 W. 43rd Street, New York 36, N. Y. LUxemburg 2 -1500

AUDIO ENGINEERING MARCH,0 1953 45

www.americanradiohistory.com EDWARD TATNALL CANBY THE COLUMBIA 360 hi -fi phonograph, pic- Filling the Great Gap firm, by chance, should have some other tured on the January cover of Æ and special interest in the phonograph -say in described in this issue, page 28, is not records -then so much the better. There going to replace your present hi -fi system. outfits that fill this rea- in this aren't many large It's not supposed to. Its speaker facilities magazine may have shown you, is description. Only one has showed well launched by now. The cycle is almost sonable will not compare with your Lansings and complete. up so far -CBS -Columbia. Altecs and Jensens and Klipsches, your Come to think of it now, it was inevitable Almost -but for one very large and CBS should come to this. CBS EV, Brociner, Bozak, University, Wharfe- complex factor, the sales systems. The final that dale, Hartley, Barker (whew I'm launched the LP, then found itself selling ... dealers in phono equipment are now, as in only trying to be impartial....) systems, above- mentioned, LP players; the CBS -designed cartridge ranged in two camps, matched the LP record's quality nor should it. The amplifier is probably championing the list and the net. Perhaps them not pretty well -but the home radios and pho- in a class with the Williamson or Mc- those terms no longer mean much, but the nographs that took over the reproduction Intosh designs (though it is push -pull). divergency of the sales camps, and of the bottle -neck sort. entire behind were obviously of the The new ceramic cartridge is unlikely to systems them, is plain enough. Stressing quality, Columbia practically unseat your present excellent magnetics Hi -fi as we know it can't sell in retail talked itself into completing the job, de- (though it's not far behind them in sound shops. Not unless it is priced about the system for same signing a complete improved quality). The changer is just a good as elsewhere (i.e. in wholesale houses, the mass phonograph trade. This, then, is changer, more or less like sound salons, etc.) -at net. We've gone attempt to break many another. too far to have the first really planned I've had one of these machines two prices for the public at across the big barrier, between hi -fi and for a week a 30 per cent differential. The list price or so and I can vouch for the above. the standard phonograph. That gap has is out. And, unfortunately, the net price this column's concern ever since it Nevertheless, there hasn't been anything isn't figured to allow the local dealer his been like this before. This machine is a phono- relatively began and so this disquisition was also in- large cut on local, small -volume evitable. graph intended to break the low -fi market sales. In other words, the hi -fi business wide -open, I'd say-and it is not hard to runs on a new basis that simply is not Stacking it up see why it might. adaptable to the old system in any large Lest we forget ... there is a vast gap way. Hi -fi has its own outlets. How, then, does the 360 stack up? Again, between the quality of the usual home ma- it's not for you and me. But that isn't the Look at this as a home phono and chine in terms of sound and that of the Basic Redesigning point. hi -fi systems we've been assembling from study it for signs of genuine departure separate units these last years. Need we I'm no sales expert and I go no further from the dismal norm. expatiate? This is an old story, to most of in this path except to suggest that the way To this day, most home phonographs us. The gap is the greater, moreover. be- towards direct improvement of the home practice the law of the 4000 -cps top. No cause most hi -fi equipment sells at the phonograph according to hi -fi concepts is highs are better than distorted highs. A nominal net level, whereas the usual home not through present hi -fi components; not vast number of problems in distortion are phonograph comes from a local dealer who through any kind of juggling of present thus simply avoided. The Columbia 360 sells strictly list. The two lines aren't even equipment, to compete with itself. easily encompasses the range to 10,000 cps, sold through the same dealers, nor via the Instead, improvement must come from and that with low distortion by anyone's same sales mechanisms. the other side. via a basic redesigning of listening standards. As the hi -fi industry gets bigger, it inevi- the old- fashioned phonograph, via the de- To this day, most home phonographs are tably must approach the mass -produced velopment of new ways to incorporate hi -fi open-backed (maybe I should say all . . . standard phonograph, in simplicity, conven- ideas, procedures, equipment, circuits, into and produce no low bass. Even the big ience, above all what I might call one - "ordinary" phonographs that shall be no ones. This machine, with a closed cabinet piecedness. This column had a lot to say ordinary ones at all. That means high tech- -when the lid is down-gives a lower bass last summer (2E August, 1952) about the nical ingenuity, imagination, ability to than most larger home -type consoles. hi -fi cycle from unwired professional sep- make a brilliant compromise and a right Rigged, and definitely somewhat boomy arate components through pre -wired and one at every point-for this is a "best - bass, but it's there. The bass balances the pre -plugged units (recommended here back under- the -circumstances" kind of job. extended high end, and a vital problem is in 1947, as I remember), "package" sys- Who shall build such machines? Not a solved. tems, the super -package mounted complete smaller concern; a large business potential The 360 shows at many points the kind in your choice of cabinet, and finally the is needed, to develop and product- engineer of ingenuity that makes a gadget man beam. one -piece separate -unit machine, sold ready radically new types of components, to build The best thing in it, to my mind, is the to play, a phonograph on the outside but the whole at an economical cost. Not likely new cartridge. Ceramic, and the first to a separate-unit, net -priced hi -fi system on a firm already in the business, either. Too rate as wide -range, it has a revolving the inside. That last development, as ads much vested interest in things as they are. needle-shank with two points which rests Rather, it must be a big firm coming very simply in a tiny yoke where the or- new, fresh and unprejudiced into the field, dinary point would be. The entire assembly 780 Greenwich St., New York 14, N. Y. with its industrial hands untied. If that snaps out in your hand via a single clip ;

46 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com the

In music, listening quality is everything. It is the No. 1 MUST. Without it everything else becomes meaningless. The AUDAX CHROMATIC has that quality to a degree not equalled by anything known -this according to the thousands of AUDAX users, lltDDE 1 themselves.

Be it diamond or sapphire, every stylus has only a limited life span; the diamond of course, lasts the longer. Obviously, then, replaceability -at home -is of greatest importance. AUDAX is engineered for easy replaceability of the stylus -at home. Of further importance is the fact that each PULL 2 AUDAX CHROMATIC stylus is replaceable independently of the other.

* The magnetic attraction between pick -up and steel turntable, known as the "HIDDEN- PULL ", has always been a problem. When point-pressure was 100 or more grams an additional "HIDDEN- 3 PULL" of 10 or 15 grams was of no consequence. Today, however, with point -pressure below 10 grams, the "HIDDEN-PULL" becomes a very serious factor.... The Audax CHROMATIC is free of "HIDDEN- PULL ". Only You can decide what sounds most pleasing See and Hear the Audax CHROMATIC and -you- be the judge.

Audax costs no more than ordinary pickups

Available with the new Compass-Pivoted Audas arms and to fit the high quality record changers

*See Pointer 84 in 1953 ELECTRONIC PHONO FACTS obtainable from your distributor

AUDAK COMPANY POLYPHASE HEAD t arty E m 500 Fifth Avenue New York 36

O RIG HT tax ]]'rr ®d t5 rpm Creators of Fine Audio -Electronic apparatus for over 25 years

tuna LEFT or 70 rpm ,Jhe Standard 4 Which OElrs judrd and Va[ued "

www.americanradiohistory.com the two grooves are played without the cartridge moving at all. The entire unit is Newest Member an inch or less long and less wide than a pencil. It fits standard mountings. The unit of a famous is made by Sonotone- another new entry HI -FI family... in the field-and I'm told will be available separately. If so, it should make a good "front end" for replacement and other use. I haven't made direct comparisons but I'd say it equals or surpasses the CAC crystal, the former Columbia work -horse. It is far simpler than the twin CAC -D and should easily outmode it. The 360 amplifier shows up in the final sound. Suffice it to say that a lot of imagination was needed to design a push -pull amplifier into an ordinary phonograph, where in a million earlier models a single - ended horror was considered quite sufficient! Don't lose our perspective on this. How to get low bass from a small box? A familiar problem these days. The entire inside space here, with lid down, is a closed chamber for two six -inch speakers, one at HI- FIDELITY FM -AM TUNER each side of the box. Open the lid and the Model =AF -723 bass departs, rather dramatically. The two n speakers, I gather, are alike except that the cone resonances are purposely slightly V istinguished for maximum performance at the lowest price pos- different, for smoother over -all response. sible for a luxurious High -Fidelity Tuner. Engineered with the pre- Sidewise Music cision that has characterized all of the world- famous Pilot elec- I find that the sidewise distribution of the This tronics instruments, over a period of 33 years. magnificent new sound via the two speakers, aiming away PILOTUNER incorporates many superb features hitherto unheard -of from each other, is the best and most dra- machine's sound. Look in its moderate price class. Write now for a full description of matic aspect of this - - straight at the machine and the music this outstanding Model #723 PILOTUNER ... Selling price, $79.95 comes not directly from it but instead seems to be "in the toom," without a sharply defined source. Couldn't be better. PILOT RADIO CORPORATION (Of course the machine's position in the 37 -06 36th Street Long Island City, New York listening room is a large factor. A nearby corner or close -to side wall will do more drastic reflecting. The machine sounds best when there is a good distance to right and left of it, with good reflecting surfaces where the sound finally hits.) Further indications of good thinking are Now ¡oir immediate 18:112 ~e4 at the changer. /zeal in the controls. On -off is The volume control begins at low (not off) and operates as a loudness control. Instead of the usual tone control, ranging from the The 2nd Audio Anthology middle downward to the familiar muffled sofa cushion effect, the tone knob hcre allows only a slight extra roll -off in the No bigger, no better than the original Audio Features- higher highs-mostly those above the top Anthology -in fact, it's just the same size and Amplifiers range of usual phonographs -to match records and to compensate for room condi- Preamplifiers a perfect companion to the most authoritative tions. Why no more? With low distcrtion book you now have on the subject of home Tone Controls (and good records) there is no need for the old tone control. It shouldn't be pres- music systems. But it contains all new mate- Phonograph Equipment ent; for habit- ridden listeners will immedi- rial- reprints of over forty of the valuable ar- Loudspeakers ately turn it down, out of sheer mental was an intelligent idea to omit Speaker End' inertia. It ticles which have most interested Æ's readers it, and intelligent, too, to put the on -off during the past two and a half years. Tape Recorder Amplifiers switch elsewhere than on tone or volume knobs where it invites wrong settings. distributors. Customary discounts fo What else? A standard (V -M) changer. ; same light Board Cover $3.00 Paper Cover $2.00 adequate and convenient the arm as in the Columbia LP changer. Neu- A surprisingly good look- CUT OUT -MAIL TODAY tral components. ing heavily built cabinet, bowed out in Book Division, front. And that's the ordinary phonograph Radio Magazines, Inc., that may start the great gap á filling. P. 0. Box 629, Mineola, N. Y. P.S. It sells strictly through regular record- radio-phono dealers, right square in Sirs: Enclosed is my check money order for copies of the the middle of the standard brands. It'll 2nd Audio Anthology. soon have competitors, I'll wager. (Please check one/ Board Cover Paper Cover CURIOSITY SHOP

o Old Curiosity Shop. Helen Morgan, Name (print carefully) Sophie Tucker, Will Rogers, Gloria Swan- son, Fannie Brice, etc. etc.) RCA Victor LCT 1112 Address A wonderful memory teaser -reissues of a batch of very famous hits and familiar voices, ranging City Zone State from the indomitable John Barrymore (Hamlet) to the indomitable Sophie Tucker, Helen Kane

48 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com the Boop girl, Will Rogers, Casey at the Bat thumping and banging, as though a large part of the stage had collapsed! (The wooden . nuff said! Excellent technical restorations. Key props m used throughout was of a fabulous reso- Some date well back into the acoustical period; platfor nance. ) most are -to- middle electrical. Outstanding record of its type early find this a thorough AES playback curve specified on Musically, folklorists will t hodge -podge of material -some is "authentic," e Folk Songs of Hungary ( Bartok- Kodaly) , record untutored, primitive, much more is relatively pol- vol. 2. Leslie Chabay, tenor; Tibor Kozma, tt NARTB (NAB) curve specified on ished and a great deal is about as folk songy as a pf. Bartok BRS 914 record Radio City arrangement of My Old Kentucky h Big bass; European -type low (300) Home. Or Schubert's setting of the 23rd Psalm, stuff. superbly recorded Vigorous, masculine turnover; adjust accordingly which is one of the loveliest items in the set I of excitement in Hungarian Chabay's by and full a Distortion Assorted popular bands, choral arrangements lusty singing. Anyone who has fallen for gypsy Elgar, Holst, and the like, round out the show. ad Distortion in loud passages only or Hungarian rhythms as in the conventional In short, this is no document of the folk music e Extra treble preemphasis use semi -pops and the familiar Hungarian Rhapsodies - art, nor of any other kind of music, but it was to. et al will relish the genuine original here, set mgre roll -off a good show to be at, and it's fun to listen to brilliant modern accompaniments by Bartok r Flatter- than -average high end - and Kodaly. Folklore people will be interested in use less roll -off ° Ibert: Concertino da camera for saxo- the piano settings -Bartok and Kodaly have not Injection moulded plastic, quite thin phone and chamber orch. Glazounov: Con- been equalled yet in this expert use of the modern Intimate, close -to recording in good certo for saxophone and arch. V.ncent dissonant idiom to set off folk music without in liveness Abato; instrs. cond. by Schulman, Picker- the musical sense of the any way distorting PH 103 -be folk -style composers should Big, live acoustics ing. t Philharmonia original. Would o study. From older 78 discs The sax was invented long before jazz. Here's u Unresonant, deadish acoustics an item from some time back that I didn't get to o Prokofieff: Peter and the Wolf. Arthur Voice is close -up, loud review that shouldn't be missed. The Ibert, from Godfrey; André Kostelanetz G His Orch. Voice is at distance, blends into 1935 and with a nice feel of the 1920s in it, is short and amusingly skittish. The Glazounov is ML 4625 (t ) musical background Columbia is unusually Thin bass, high turnover point lushly romantic. The recorded sound Don't sniff too soon! Godfrey is Godfrey and fine, doing the maximum for the small group of ; bass you'll recognize him here all right -but his usual (600-800) needs boost instruments. Beautifully balanced sax tone, ex- elaborately off -hand style has been well adapted over normal playback cellent strings and nice bass. Pickering? Who to the Peter story in this recording, without too but our friend of the well -known pickup, Nor- much slapstick, a fairly close adherence to the to middling samples of music and dance, a few man P. He's a musician, in case you didn't know, standard spiel that goes with the music. Won't complete, most of them excerpts, faded in and out, a top -rate horn player (I hear from good critical do your extra-bright child a bit of harm. And with running 'Comment "off -. tage" (tape -edited sources) as well as a conductor, as here. the Kostelanetz music is unexpectedly warm and in). There are some stunning things here and the fresh. Part of that is due to the superb record- recording is technically excellent. But the edit- ° African Tribal Music and Dances. Sonar ing, but not all -evidently Andre has some per- ing is a bit clumsy and the mike set- ups -prob- Senghor & Co. t Esoteric ES 513 sonal feel for this music that he doesn't for many ably beyond the operators' control most of the Bush do I mean another war -horse out by his Orchestra. time often cock -eyed. Doesn't matter partic- Super -hi -fi sounds of the (or put -are Paris, ularly; but more important is that the material the 'Veldt ?), recorded "on location " -in may be a travelling Folk Music Festival (Eistedd- is not well adapted to this kind of technique. Too via a nite club hot spot! It International troupe, but the stuff is authentic sounding, fod). Auspices UNESCO. Jack Bornoff, many items are too long and must be faded in and pretty out. Much, clearly, was for the eye. It is a bit notably the rasping voices. Not a trace of "train- nain. Westminster WAL 209 ing" here! This is a kind of halfbreed music, not ft exasperating to hear . .. "and now, here are the -spot job by BBC of the international the famous Whoosis Dancers from Ireland who too far removed from Calypso though more primi- On- Native dialeet, version of the ancient Welsh folk festival. Short have won countless prizes " -followed by a vast tive (and far more complex).

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AUDIO ENGINEERING MARCH, 1953 49

www.americanradiohistory.com much shouting, drums, etc., but in between the catchy refrains are sung in thirds, not unlike Mexican and Latin American music. A good hi -fi stunt record to have around.

"El Pili" Flamenco. El Pili; Mario Escudero and Alberto Velez, guitars. t Esoteric ES 2001 110 ") Another in the same series -Jerry Newman, who started Esoteric as an off -shoot to his New SOflOCRAFT York record shop, sold the shop and bought him an Ampex and- Telefunken. lie's travelling. These are evidently famous names, but my ear detects a bit of international sophistication and show biz QUALITY, DEPENDABILITY, SERVICE in the music. (They are also parts of travelling troupes.) Some too -slick harmonies, etc. Only a trace; the rest is fine and recording is excellent, if a bit close -to.

"Mr. President"-from FDR to Eisen- hower. 1933 -1953. Edited and narrated NEW ?IaqiieetrdttVOYAGER" by James Fleming. RCA Victor LM 1753 The patch it- together documentary history, combining commentary with the actual voices and SINGLE CASE sounds of the past, is now a familiar and irre- sistable medium. Columbia has been at it on LI' Portable for some time; this is RCA's follow up. In many ways this is a step forward. There is much new material here, little that is already familiar; all Magnetic sorts of people pop up- Woolcott ( "the Town Crier "), Sinclair Lewis, Huey Long, Ickes, Tape Recorder Landon. The commentary is less editorial sounding (and less paternal in tone) than the CBS work, the excerpts more varied. Recorded voices $485 net succeed each other without intervening com- AVAILABLE IMMEDIATELY mentary, often answering each other, presenting different sides of arguments. Many voices speak only a few words, but they are usually well This professional very unit consists of the t. chosen. The New standard PT6 -AH recording mechanism familiar Deal years, build -up plus light-weight amplifier. Amplifier ... to war are covered with new material, the war has two inputs -one microphone, bal- is passed over rapidly. anced or unbalanced, 50 ohm imped- Best work is side 2, where the pace lengthens ance (easily converted to 200 ohm( and one high imped- out to cover the recent events in detail, with ance unbalanced input. Output is 600 ohm, balanced or Dewey, Truman and Stevenson getting -or giv- unbalanced, with maximum output of 6 dbm. Earphone ing-an excellent accounting. How time flies! monitor jack. Frequency response ± You'll find all Magnecord equip- 2 db from 50 to 15,000 Main faults in this disc: some uneven timing cycles at 15" /sec. Portable carrying case has amplifier and ment available at our offices. recorder mechanism (Fleming's voice is occasionally hurried or tired, back to back when closed. Unit is Trained engineers will give you joined by slide hinges, and amplifier may be detached and between good stretches). The counterplay of operated beside mechanical unit. Weight 45 lbs., dimen- expert advice and immediate serv- voices is sometimes confusing; you lose track of sions 19" x 73/4" x 17iß". ice with genuine Magnecord parts. who's who, or where we are, especially on the first side. Not serious, in a tremendous under- taking of this sort. Technical work on the older voices is excellent. (Or maybe NBC just has good recordings.)

0e Dvorak: Serenade, op. 44. London Ba- roque Ensemble, Haas. Decca DL 7533 A novelty item by a familiar composer, a serenade not unlike the wind divertimenti of Mozart -this has a cello and double bass but the rest of its instruments are winds. 2 oboes, 2 clarinets, 2 NEW bassoons, contra -bassoon, 3 horns. With that potent armament Dvorak produces some fine vil- lage -band stuff with a solid tone quality that is beautifully recorded as well as nicely played. PORTABLE BATTERY fl't Sixteen Sonnets of William Shake- TAPE RECORDER speare. David Allen; music by Curtis Bie- ver, played by Margaret Ross, harp. Records Anything .. . Poetry Records PR 201 (10 ") Anywhere ... Anytime Good reading, the harp music an unobtrusive and legitimate way of coping with the difficult problem of a plain, unadorned voice on records - complete, $295 net which never seems to work out well. Voice is somewhat tubby in quality, very slightly distorted. Allen should experiment on this score for future releases, to find where trouble is. Too close

Smaller than a portable typewriter . . . to mike? Too high a tape level? Tape alignment? Write, phone or stop in for butt into a handsome briefcase more information. Your sound completely battery operated! Wet cell and recording problems will receive battery for 11 /z hours operation, re- e Cluck: Flute Concerto in C. Corelli: Oboe prompt, courteous attention. chargeable from car or charger. Dry Concerto. Paris Philharm. Orch., Leibowitz. cell "B" battery good for 50 hours. Microphone with stop and start switch. Haydn: Toy Symphony. Orch. Radio - Immediate playback through phones Symph., Leibowitz. OCS 29 Speed 71/2" /sec. and 33/4" /sec.: weight Two pleasing concerto items concerto from 127s lbs.; dimensions 55/s" x 131 x -a Gluck is a decided novelty since we normally 1 2 /4 ". hear only his operatic music, and the Corelli con. certo has in it a famous sarabande that you'll SOflOCRAT recognize from popular transcriptions. The Haydn CORPORATION Toy Symphony is for once done without putting those d - watery bird whistles and rattles 3 Headquarters for Sound & 115 WEST 45th STREET (3rd floor) inches from the nearest mike, and it sounds a lot better, remains as good fun as ever. Playing has Recording Equipment Ness to Timer S yore NEW YORK 36, N. Y. & Accessories that hard, chromium quality that Leibowitz likes LUxemburg 2 -1750 so much (and I don't). Nice hi -fi, and the crow call ( ?) is out of this world.

50 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com ° Menotti: Amahl and the Night Visitors. IN THOSE EXTRAORDINARY APPLICATIONS Original cast of the NBC telecast (with Chet Allen). RCA Victor LM 1701 WHERE DEPENDABILITY AND PRECISION COUNT If ever a modern classic was tossed off for eternity, this is it. Menotti has a peculiar genius for cutting across styles and tastes to appeal to almost any and everyone--his drama similarly seems to "work" in any modern medium, where other modern composers flounder abysmally with you'll find the technical difficulties. All of that shows here superbly: the pomp and circumstance of N BC super -TV can't touch the simplicity and direct- ness of this music and story I Records bring it through as movingly as TV or stage, or what - have -you. And this music, done in a hurry by Menotti, seems to hit the essential spot that earlier and more pretentious undertakings -the Consul, for instance-missed for most of us. I tOcetitliTotikatr can guarantee enjoyment to absolutely anyone here. The recording, too, is superb. If RCA had chosen to do this sort of job throughout its modern catalogue, what hi -fi riches we'd possess. Ter- rific. A ''LOCATOR" FOR SURGERY Zwei Herzen im 3/4 Takt. (Two Hearts in Three -Quarter Time.) Viennese Light Opera Co., Stolz. Period RL 1902 " Der Bettelstudent (The Beggar Student). The Kirby -Thurstone Cholelithophone Viennese Light Opera Co., Stolz. is an ingenious electro- acoustic device for Period RL 1901 the detection and location of gallstones in the common and hepatic ducts. This Viennese light opera, dating from the incom- fine aid to surgery is a joint development parable Johann Strauss, dies hard. The Beggar of the University of Pennsylvania Student (Milloecker) dates from 1882, the fa- Hospital and Pennsylvania State miliar Zwei Herren from 1934, and the style is College. The precise and depend- the same old melange of waltzes and nice, juicy, able instrument is manufactured sentimental polkas. but an inquiring ear will find by Centre Electronic & Mfg. Co. the Milloecker of 1882 considerably better stuff, CHICAGO Sealed -in -Steel trans- and nearer Strauss, than the dismally watered- formers are specified and used down Zwei Herzen, which Stolz himself wrote exclusively for the completely in 1934, following the success of the song itself. dependable performance Superb and natural recording, the words par- required of the instrument. ticularly clear, the voices undistorted.

CHORUS, ORCHESTRA, SOLOISTS . C -TYPE I Mendelssohn: Walpurgisnacht, op. 60. Sealed -in- Netherlands Philh. Choir Fi Orch., soloists, Steel, with Ackermann. Mendelssohn: d Five Songs. leads and Uta Graf, sop. Concert Hall CHS 1159 flange mount The list of major works that have rarely been heard until LP brings them back still isn't complete. Here is some of the very best Men - delssohn there is, a short oratorio or cantata based on the Goethe romantic tale of the night SAFETY FOR A of devils and witches. This music is dramatic, SUPERLINER like Elijah, but simple, intense, un- stuffy, like the Midsummer Night's Dream. Beautifully sung, in a well balanced recording. The five piano songs Photo Courtesy Newport News are lightly and expressively sung by a lovely high Sn,ybldg d Dry The S. S. United States - word in soprano -last voice, Uta Graf, with good piano ac- Dock Co Superliners -- incorporates every known sea- companiment. Somewhat distorted. Chorus dis- going safety device. Among its electronic torts a bit in loud parts. safety features is the Announcing System Amplifier, designed and built by Electronic ,II Beethoven: Ruins of Athens, op. 113. Engineering Company, Inc., of Norfolk, Neth. Philh. Choir U Orch., soloists, Goehr. Va. The power transformer specified Concert Hall CHS 1158 and used in this super-dependable amplifier is by CHICAGO. Where A companion Concert Hall restoration, again dependability is an absolute beautifully done and of considerable interest - requirement, you'll find this is one of those works of which we hear CHICAGO -- the world's only the overtures, forget about the rest. The rest toughest transformers. isn't great Beethoven but it's highly attractive and parts are priceless, the sort of music it is just impossible to imagine as unknown. Some fine pseudo- Turkish music, including the familiar S -TYPE one, too, Turkish March. This distorts in the Seoled -in- louder parts. Too high a level at the tape re- Steel, with lug corder input stage, I'll bet. (Remember that the terminals and naturally complex "beats," quick transients in flange mount vocal music, don't register properly on a damped meter.)

Free "New Equipment" Catalog ,kI Prokofieff: On Guard for Peace, op. 124 (1950). Combined Choirs, State Orch. of You'll want the full details on CHICAGO'S New Equipment line, the range "Sealed U.S.S.R., soloists, Samonsoud. covering complete of -in- Steel" transformers for every modern circuit application. Write for your Free copy of Vanguard VRS 6003 Catalog CT -153 today, or get it hoer your electronic parts distributor. If you can bear to associate yourself with Stalin & Co.. long range, you'll find our old sAN friend Prokofieff, he of "Peter and the Wolf," "Alexander Nevsky," the Classical Symphony, in excellent form lure. Politics haven't spoiled this man, by a lung shot. There's a lot of bombast Export Sales Div.: and a good deal of padding, to please the politi- CHICAGO TRANSFORMER Scheel International, Inc. cos, but in between, you'll find some of the most 4237 N. Lincoln Ave. DIVISION OF ESSEX WIRE CORPORATION poignantly moving music you'll hear in a long Chicago, Ill., U.S.A. time and some incredibly fine singing. The con- 3501 ADDISON STREET, CHICAGO 18, ILL. CABLE ADDRESS: tralto soloist has a voice you'll hardly believe, HARSHEEL

AUDIO ENGINEERING MARCH, 1953 51

www.americanradiohistory.com combining tenor, alto and soprano in one vast and beautifully controlled instrument of unheard-of power; the contrasting boy alto solo and the children's choir, contrasting with the adult choir, are other elements in an unforgettable kind of listening. 11-hat a language that Russian is, for singing! Yep, Prokofieff has his cake and eats it ; he writes what the commissars ask for and manages to make it good music as well. The recent "Re- forestation" oratorio of Shostakovitch (VRS 422), an outwardly similar big piece, is by comparison a servile toadying to the policy makers. Loud parts blast badly. Same story, probably.

FREE! - 68 page catalog section from Radio's Master. REISSUES. Note: The reissue of notable 78 recordings on Catalogs the products of 30 manufac- LP has been greatly stepped up; economics- turers of Recording, Phono Equipment thank Heaven -now favor this procedure and and Accessories. the sets that once were semi-white elephants (anyway, they cost a lot and weighed more) Complete descriptions, specifications and now reappear trimmed to LP (and 45) convenience. We are now getting into the big -set area, illustrations of such products as: Record- those huge tomes that, most of us thought, were ers, Phono Motors, Turntables, Record gone for good except as collector's items. Best Changers, Cartridges, Pickups, Discs, news of all for a lot of Æ readers: Tape, Needles, etc. ob The Mikado. D'Oyly Carte Opera Co. RCA Victor LCT 6009 (2) obd H.M.S. Pinafore; Trial by Jury. D'Oyly Carte. RCA Victor LCT 6003 (2) At long last, the ancient and honourable G & S ros, albums, beloved by generations, are up for reissue! About time. Most Savoyards agree that 7 .oc +r these are better performances than the new hi -fi ones of recent date by the same troupe. Technically the operas rank upward from Trial by Jury, which is tubby and somewhat distorted at best, through Pinafore, similar but decidedly a better, to the best of the three, Mikado -clear as a bell and surprisingly bright. All are intel- a ligible and enjoyable. Better use 300 -cps turnover; the bass is pretty heavy.

0° Gounod: Faust (Highlights). Royal Phil-

harmonic, Beecham : French soloists and Represented in RADIO'S MASTER 68 page Recording & Phono Equipment chorus. RCA Victor LCT 1100 Booklet are the products of the fallow- Among a whole of opera reissues this ing manufacturers: group stands out as extraordinary. Throw out all your Alliance Manufacturing Co. Fausts American Microphone other and try the real French style! If Co. you haven't the wonders Ampex Electr c Coro. discovered of the French 'Amplifier Corp. of America vocal style, which makes the voice a musical in- The Astatic Corp. strument as accurate as an oboe or a violin, the Audak Company astonishing Geori -Bone, also heard in Uraniá s Audio Devices. Inc. new Thais (Massenet), try her and marvel. Faust tyrrNn "s. Bell Sound Systems. Inc. with this treatment (and old Sir Thomas knows Berlant Associates o v ,e enough to get his singers straight from France) tRÑe, Bogen Co.. Inc. Clarkstan Corp. is believable, beautiful; in many U.S. perform- Duotone Corp. ances it is dismally corny. Too bad the entire re- E lectroVoice. Inc. cording is not released. It ranks very nearly hi -fi, Aerua/ Fairchild Recording Equipment Co. with fine edge and sibilants. ssze g., Garrard Sales Corp. x lOti,. General Electric Company General Industries Co. °Fv" Strauss: Der Rosenkavalier (abridged). Jensen Industries. Inc. Lotte Lehman, Elizabeth Schumann, etc. Magnecord, Inc. Masco Electronic Sales Vienna Phil., Heger. M. A. Miller Mfg. Co. RCA Victor LCT 6005 (2) Minnesota Mining 8 Mfg Co. Newcomb Audio Products Co. A famous early recording by the now -retired Orrad io Industries. Inc. first lady of song, along with her famous col- You can obtain without cost or obligation, a complete 'Pentron Corp. league, Schumann. This one is technically so -so, 68 page catalog section as reprinted from the Indus- Permo, Inc. for two reasons: I) the highs are dismally lack- Pickering 8 Co., Inc. ing- probably had to be filtered in the copying- try's Official 1100 page Radio's Master, 16th edition. Presto Recording Corp. the sound is muffled; and 2) the old technique Recordist Corp. of recording voices at stooge distance was used; This section catalogs in detail the products of the lead- Recoton Corp. the singers are mere threads ing Recording and Phono Equipment manufacturers Reeves Sou ndera ft Corp. of tone at times, lost Rek -O -Kot Company in the orchestral sound. For those who love Leh- all 1 - in handy booklet. It is complete with descrip- Shure Bros.. Inc. mann- and Strauss -tine music will get through. tions, specifications, and illustrations as written by V -M Corporation each manufacturer. Whether you Walco Products Inc. buy, sell, or specify Webster -Chicago ORCHESTRAL SERIES these products, you will find this booklet Corp. extremely Webster Electric Co. on helpful. 'These manufacturers not included Strauss: Dance of the Seven Veils (Sa- in Radios Master section. Separate lome) : Rosenkavalier Waltzes. This offer is MAIL TODAY catalog sheets will accompany each Decca DL 4032 to k'et (10 ") made possible r Tchaikowsky: Waltz, Polonaise (Eu- by a special ar- gene Onegin) ; Andante Cantabile. rangement be- AUDIO ENGINEERING Decca DL 4033 (10 ") tween AUDIO All the with P. O. BOX 629, MINEOLA, N. Y. above N.Y. Stadium Con- ENGINEER- certs Symphony, Smallens. ING and the Please send nie, without cost or obligation, the 68 page Recording & Phono The popular 10 -inch LP's are issued too fast publishers of Equipment and Accessories Booklet reprinted from for Radio's Master. any human reviewer to keep up with I Not in RADIO'S ones but in series. Best thing is to look at a MASTER. Be group of a kind -since nowadays a recording Name sure to get your session usually gets down a whole slew of works copy now. Fill with a given musical combination and engineer- Address ing set -up. in the coupon The Stadium Orchestra is the N.Y. Philhar- below and mail. City Zone State monic in contractual disguise. This series features

52 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com high -quality recording, distant -mike technique, in a big, resonant liveness. A bit too distant, con- fused. Deccá s recorded curve has sharp highs, a high (800 ?) turnover; adjust accordingly.

"r Mozart Overtures, vol. 1 (Cosi fan tutte, Don Giovanni, Magic Flute, Cle- menza di Tito). Vol. 2 (Seraglio, Marriage of Figaro, Idomeneo, Impresario). Berlin Philh., Fritz Lehmann. Decca DL 4035,6 (10 ") Lehmann should be a fine Mozart conductor - but space limitations wreck this series; they are all played impeccably, but too fast, and exactly alike, as though they were no more than so many brilliant curtain-raisers. One can carry this mania for overtures too far!

Mozart: Magic Flute, Don Giovanni Over- tures. London Symphony, Krips. London LD 9001 (10 ") ° J. Strauss: Vienna Blood; Wine, Women and Song. London Symphony, Krips. London LD 9013 (10 ") London might seem to give half-value -only two overtures instead of four per ten -inch disc; but this is a much wiser procedure. Here there is room for expansion, proper interpretation, and the engineers, too, aren't confined. Krips gives his overtures their full dignity, but the playing is a bit lack -lustre, lacking the intensity that should be here. But his Strauss Waltzes (see also Blue Danube and Emperor, DL, 9015) are superb-sweet, ethereal, yet solid too, without the usual exaggerations of tempi, the half -bored hack - ing-away at the old familiar tunes. London's black -label technical work is as good as any ffrr. Price is determined by volume sales, evidently.

° Beethoven: Prometheus, Fidelio Over- tures. Egmont, Coriolan Overture. Leonore #3, Consecration of the House Overtures. London Philharmonic, van Beinum. London LD 9024, 21, 22 (10 ") Six major Beethoven overtures, well spaced out for unhurried playing. Somehow, van For those interested solely in the finest possible repro- Beinum's performance misses much of the power of these giant works. Choppy, quite slow, but duction of music from recordings this Altec system is beyond that the lyric melodies are unphrased, The chairside control unit don't flow, the continuity is not good. the string beyond compare. beautiful playing is weak. Fine recording, with some re- has a record crossover switch, fully variable bass and markable examples of low -level cutting -a thread of sound, no more -in Leonore .*3. Surfaces treble rise and droop controls and a switch for the allow it now. Fine technical quality may decide you to get this set. selection of radio, tape or other sound sources. The 20 watt amplifier has less than 2% harmonic distor- al).- Mozart: Symphony #36 ( "Linz ") ; German Dances, K. 600. Winterthur Sym- tion and is completely controlled from the hairside phony, Goehr. unit. The famous Altec "duplex" completes the sys- Mus. Masterworks MMS 1 (10 ") agie tem. These "duplex" speakers are the finest in the Mendelssohn: Symphony #4 ( "Ital- ian"). Winterthur Symphony, Dahinden. world and are guaranteed to reproduce all of the Mus. Masterworks MMS 3 (10 ") aile tones from 30 to 22,000 cycles when mounted in the Haydn: Symphony #96 ( "Miracle "). Overture to Isola Disabitata (Uninhabited handsome Altec 606 cabinet. If you want the finest Isle). Winterthur Symphony, Goehr. Mus. Masterworks MMS 6 (10 ") record reproduction you want this wonderful Altec This is Concert Hall's new low priced line, on system designed just for records. thin injection-moulded discs, and it's a musical bargain. The Winterthur Symphony plays with a peculiarly nice off -hand, intimate, chamber music style, very musical, soft -textured. Three splendid symphonies done in this manner, plus two Mozart dances and an unheard -of Haydn overture. 1. "Duplex" louOaeaker 2. 606 corner cabinet a Mozart: Symphonies #1, #2, #5, #6. Symphonies #4, #10, #11, #14. Win- 3. A -433A contro Init terthur Symphony, Ackermann. 4. A -333A amplif er Concert Hall CHS 1165, 66 e Mozart: Piano Concert #1, #2, #3 (After J. C. Bach). Winterthur Symphony, Ackerman. Concert Hall CHS 1164 If you ever wondered about the early Mozart works in these categories -here's your music, in another fine series played as in the Masterworks . records, above. These are youthful Mozart, the 3. composer first finding his stride in the orchestral medium. He was nine years old for the earliest, See and HEAR the complete eleven for the latest! But don't expect amateur- ishness -these are short, simple but astonishingly ALTE C Altec "home music system" at your competent and expert pieces, easily equal to the nearest high fidelity studio. mature works of his leading contemporaries in the same vein. Listen and try to believe your ears! A set for all Mozart collectors. 9356 SANTA MONICA BOULEVARD, BEVERLY HILLS, CALIF. 161 SIXTH AVENUE, NEW YORK 13, NEW YORK

AUDIO ENGINEERING MARCH, 1953 53

www.americanradiohistory.com NEW PRODUCTS

Reverberation Unit. Both the inconveni- eration, the R701 features a variable band- vere shock, vibration, and acceleration. ence and expense of echo chambers are width i.f. channel which permits selection Available in standard resistances of 250 to eliminated through use of the new Model of maximum wide -range response or maxi- 10,000 ohms with power rating of 0.25 40 Reverberation Unit, recently announced watt, Trimpots are manufactured by by Audio Instrument Company, Inc., 133 Bourns Laboratories, 6136 Magnolia Ave., W. 14th St., New York 11, N. Y. An im- Riverside, Calif. proved version of the Goodfriend-Audio Facilities Co. artificial reverberation gen- Preamp and Matching Tape -Transport erator which was first introduced three Mechanism. Designed for installation in years ago, the unit is a multiple -head mag- custom cabinets, the new Pentron Model netic- tape -loop device which is compact, PRE -7 preamplifier and Model 9T -3M tape convenient, and flexible in adjustment. In transport mechanism make up a complete operation, the input signal is recorded, tape recorder and playback assembly for then reproduced by several magnetic heads use with any existing audio system. Preamp control panel is equipped with

mum selectivity. A 10 -kc whistle filter eliminates inter -station interference. The tuner is equipped with continuously variable bass and treble controls and a 6 -position function -selector switch. Among other notable features are: a built -in preamplifier with compensation for GE, Pickering, and Audak pickups; cathode -follower output circuit, and automatic reduction of voltage on all but audio tubes when tuner is used with phono input. Audio output is 3 volts at 6000 ohms, with only 0.2 per at different times. The reproduced signals cent distortion. Frequency response is are returned to the recording head, and within ±0.5 db from 20 to 20,000 cps on passed around the recirculation loop again FM, from 20 to 4000 cps on normal AM with diminished amplitude. In this man- and from 20 to 7500 cps on broad -band ner, the signal is caused to decay in the AM. Further information may be obtained same fashion as sound diminishes during from David Bogen Company, 29 Ninth multiple reflections from the walls of a Ave., New York 14, N. Y. room. A switch control permits changing the number and position of reproducing Compact High- Pidelity Amplifier. An heads. Reverberation time is adjustable up improved version of the Grommes Model to 10 seconds. Ratio of reverberant to LJ "Little Jewel" amplifier, designated direct sound may also be widely altered. Model LJ2, features frequency response The unit contains a zero-loss straight - within ± 1 db from 20 to 20,000 cps at 3 through channel, as well as the tape -loop watts output. At rated power output of 8 reverberation channel, so that no audio watts, harmonic distortion is 1% per cent system circuit changes are necessary. and intermodulation is 4 per cent. Inputs motor switch, pilot light, magic -eye re- Supplied for rack mounting on an 8% x 19 cording level indicator, tape -radio switch, panel. volume -tone control, play record switch, and jacks for phonograph, tuner, microphone, output, and monitoring. The trans- High -Output Magnetic Tape. Many im- port unit permits choice of 3.75 -in. or proved qualities are inherent in the new 7.5 -in. recording speed. Separate record No. 120 "Scotch" recording tape recently and erase heads have removable pole announced by Minnesota Mining and Man- pieces which can be replaced as simply as ufacturing Co., 900 Fauquier St., St. Paul, a phonograph needle. Fast forward and Minn. Offering more than twice the output rewind will transfer a 1200 -fL spool in 40 of previous Scotch tape, the new tape Is seconds. Both units are available together designed especially for use in radio, TV, as Model PMC in a single luggage -type carrying case for portable use. Complete technical specifications will be mailed on request to The Pentron Corporation, Dept. AE-3, 221 E. Cullerton St., Chicago 6, Ill.

Low -cost VTVOM Zit. Frequency response as high as 2.5 mc, adequate for servicing TV circuits as well as audio are supplied for magnetic pickup, micro- equipment, is one of the features of the phone, crystal pickup, and tuner. Treble new Knight vacuum -tube volt- ohm -milli- control affords 18 db cut at 10,000 cps. ammeter kit recently announced by Allied Base control permits 15 db boost at 50 cps. Radio Corp., 833 W. Jackson Blvd., Chi- Hum level is 80 db below 8 watts. Output cago 7, Ill. Among its 29 ranges are six impedances are 4, 8 and 16 ohms. Com- plete information will be supplied by Pre- cision Electronics, 9101 King Ave., Frank- lin Park, Ill. Small Wire -Wound Potentiometer. De- signed for precise circuit trimming in and recording studios, in computer work, miniaturized equipment, the new Bourns and in other critical applications. It pro- Model 120 Trimpot is so tiny that 40 of duces at least 8 db more output at a given the units occupy less space than a stand- distortion level over the full audio range ard package of cigarettes. Adjustments than tapes previously marketed, thus per- are made by turning an exposed slotted mitting an 8 -db greater signal -to -noise shaft with screwdriver. ratio on conventional professional tape re- a Resolution as corders. Of particular value in the sound recording field, the new No. 120 tape will permit improved quality in recordings, with greater dynamic range. Aside from the fact that it is dark green in color, and employs a coating material with increased magnetic remanence, it is identical phys- ically with conventional tape. It may be used interchangeably with conventional tape without bias adjustment.

High-Quality PM -AM Tuner. Remark- able sensitivity permits excellent FM reception in areas where It has heretofore been impossible with the new Bogen Model R701 14 -tube tuner. Designed for high - quality custom installations, the tuner requires only a 3 -mv input for 30 db quiet- ranges for measuring a.c. peak -to -peak ing. Push- button control permits switch - volte, six milliammeter ranges, and five in or switch -out of a.f.c. action. Protec- low as 0.25 per cent is obtained over the capacitance ranges. Maximum d.c. range is tion against drift is afforded by tempera- 25 -turn adjustment range. Electrical set- 1000 volts, and maximum a.c. range is 2800 ture- compensated oscillator. For AM op- tings are securely maintained during se- volte. Resistance and capacitance ranges

54 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com are 1000 megohms and 5000 microfarads, respectively. Special probes are available for extending the d.c. range to 30,000 volts and the a.c. frequency range to read r.f. DESIGNED FOR HI -FI PERFECTION! to 200 mc. All voltage functions are elec- tronically protected against burnout. Intercom Sytem. A baseboard- mounted TANNOY 12 DUAL power supply, self- compensating to deliver required power to all or a selected CONCENTRIC SPEAKER group of stations, is featured with the new 20 -watt Redi -Power Talk -O- Phone, recently introduced by Talk -O -Phone Co., 130.00 net 1512 S. Pulaski Road, Chicago 23, Ill. Internationally acclaimed for amazing response range, balance Although retaining the compact size of and definition, the Tannoy gives you uniform response from 35 to 25,000 cycles. Power capacity, 15 watts; Bass resonance, 35 cps; crossover frequency 1,700 cps. 15" speaker, 25 watt peak 159.00 GARRARD RC -80 RECORD CHANGER 41.45 net Less cartridge The Garrard plays all three sizes (7 ", 10 ", 12 ") and all three speeds (33 -1 3, 45, 78 RPM)! Completely automatic, with switch off at end of last record. Tone arm returns to rest position. Adaptable to either 110 or 220 V. Complete with 45 RPM spindle and two empty shells. BOGEN R701 earlier models, the new Talk -O -Phone offers a number of additional engineering I features. Uni -Trans dictation control elim- FM -AM TUNER inates the need for operating any controls while dictating. Twelve, twenty, thirty, or 145.20 net E, forty station capacity can be housed in É- the same cabinet, and the system can be Full frequency range of 88 -108 MC FM, expanded or altered at any time without on 530 -1650 KC on AM; discarding the original equipment. frequency response of 20- 20,000 cps. ±.5 db on FM; built in preamplifier, AFC, AFC defeat switch, low distortion; hum level - PM -AI[ Tuner. Newest in the line of 65 db below. 1 4 tubes including power sup- high -fidelity components manufactured by ply. Size 15" 5 8 ' 2 " x 9 ' . Weight, 17 lbs. The Pilot Radio Corporation, Long Island City, N. Y., is the Model AF -723 Pilotuner, an 8 -tube self -powered unit which incor- CONCER.TONE 1501D porates a temperature -compensated oscillator for drift -free FM reception, also a.f.c. TAPE RECORDER which may be switched in or out at will. 345.00 net New and improved! Separate heads for high frequency erase, record and play back, with simultaneous monitoring from tape while recording. Instantaneous choice of 7tí" or 15" per second tape speed. Three synchronous, dynamically balanced motors for dependable performance. Frequency response ± 2 db, 50 to 15,000 cycles of 15" per second. Available in single or dual track. Carrying case and monitoring amplifier with 8 -in. speaker 82.50 BOGEN H010 -RXPX Inputs are provided for TV and phono. REMOTE CONTROL Tone control on the AF -723 may be switched out when the tuner is used with an audio amplifier which incorporates such AMPLIFIER 147.15 controle. Cathode -follower output permits The famous Bogen Baton combines an all -triode power up to 100 feet of interconnecting cable to amplifier and remote control. Power output 10 watts, amplifier without detracting from audio peaks to 25; frequency fidelity. The tuner is supplied with a hand- response: ± 112 db, 10- 20,000 some bronze -finish escutcheon plate for cps; Hum: 70 db below; speaker output: 12 ohms; 8 custom cabinet installation. Over -all di- tubes; Inputs: GE, Pickering; tuner; Controls: bass, treble, power on -off, selector; size: mensions are 14 x 7 x 81/2 in. Va 15" x 10" x 8"; weight: 32 lbs. Amplifier only 93.79 ERRATA Remote control and pre -amplifier 53.36 Olan E. Kruse, author of "Circle Di- FAIRCHILD 215 agrams for Resistance- Capacitance -Cou- pled Amplifiers" in the February issue, ad- SERIES CARTRIDGE vises us of erroneous figures on his Fig. 3. 47.50 The values for T along the top should tik Here's unbelievable freedom from needle talk! Equipped with - have been: 1.59, 3.18, 4.77, 6.36, 7.95, 9.54, a dia mond . . . 11.1, 12.7, 14.3, and 15.9. The stylus the cartridge is of the moving coil design. 1.0 mil tip. values for F 215C -3.0 mil tip along the left side of the diagram should 42.50 2158 -2.5 mil tip 42.50 have been : 100, 50.0, 33.3, 25.0, 20.0, 16.7, For vertical records 14.3, 12.5, 11.1, and 10.0. 50.00 Mail 8 Phone . . . Lewis S. Goodfriend, author of "The Orders Filled 25% Deposit, Balance COD Send for FREE Catalogue, Music Wide Range R -C Oscillator," also in the of the Masters February issue, advises us that the top cathode resistor in Fig. 2 should have been 68 ohms, and that the lead between the junction of this resistor and the 2500 -ohm pot and the junction of R, and the 0.5 -pf o 69 CORTLANDT ST., NEW YORK 7, N. Y. capacitor should be a 1.0 -meg resistor Dept. A 43 rather than a solid wire. In Fig. 3, page r41ia Mit 68, the top cathode resistor should have CORTLANDT 7- 0315 -9 been 160 ohms, and the 1.0 -meg resistor The House Built on Service should have been shown as described above in Fig. 2.

AUDIO ENGINEERING MARCH, 1953 55

www.americanradiohistory.com Plug -in Broadcast PATENTS "j PRE -AMPLIFIER often synonymous!) into action. With high -quality audio going strong after the buildup in interest it has undergone since á- the war, many of us seem to be finding that the quality in the best audio amplifiers today leaves little to be desired and ourselves with little to do by way of improving it -except to try doing the same thing more cheaply. As audio has developed, we have built amplifiers with wider and wider frequency bands -up to 100 kc and more. In most cases the only value of such wideband response is in achieving better operation of the high -level feedback circuits and there is more than a suspicion that we have gone to such high-frequency response sometimes just through a desire to do "something more" even though the practical value is small. Well, why not go the whole hog and PLUG-IN DESIGN -simplifies maintenance. start getting interested in video amplifica- TWO STAGE -Ideal for microphone or transctip- tion? A video amplifier is essentially a tiun preamplifier. resistance- coupled amplifier with extremely EXCELLENT FREQUENCY RESPONSE - Features low wide band -to at least 4 mc, generally, and distortion and noise level. sometimes a great deal more. As the word COMPACT...YET HIGHLY ACCESSIBLE. video indicates, the principal use for such Audio line amplifiers today is in amplifying television The G -E Plug -in Broadcast includes: picture signals; but that is by no means BA -1 -F BA -12 -C BP -10 -B the only use. Meantime, any good book on PRE -AMP PGM /MON AMP POWER SUPPLY television will give the basic approach to Por information write: General Electric Co., wideband amplification, from which some Section 4433, Electronics Park, Syracuse, N.Y. audio might well jump off to new approaches and better results than present circuits. GENERAL ELECTRIC The apparatus required is simple enough -the same old tubes, resistors, capacitors, and the like. A couple of new components High Fidelity Record Reproduction come into play-coils with small inductances, up to a maximum of around 1 milli- henry. They are easily wound or bought. Wideband oscilloscopes are available today, though they are a little expensive usually. But a long series of investigations, experi- mentation, and self -indoctrination can be had by playing with the family TV receiver. Better yet, get an old, second -hand receiver, derive signal from some convenient point in the good set (that won't harm it any way) and transmit video from the good set 7, 10, AND 12 to the second -hand one via video amplifiers, INCH RECORDS /4íG1/ 1l- %%thlifl4 attenuators, phase inverters, frequency -cor- OL rection networks, and all the rest of the possible gimmicks. Video work is just an 3 -SPEED RECORD CHANGERS extension of audio and it has the perfect field of play for the audio man with wide - banditis. In future we are going to look for a few MODEL 3 522' good video- amplifier patents. We'll write Intermixes 10 and 12-inch records them up for Æ, see if Editor McProud LIST PRICE $65.00 ._ (less base) will print them, then wait for the brickbats and bouquets in the mail! tra MODEL 3/521' Non-Intermix Model (You're on your own, Mr. p. We'll run LIST PRICE $54.50 ern, b/d on your responsibility. En.) (less base) . 'Available in cream, brown or 1- gray finish. AUDIO 1693 Li; oua page 25] haft (m) of a small Hammer bone so that its head comes close to the Anvil which is part of the ring structure (ab). RECORD CHANGER BASE 4. To cause the diaphragm to have Wood. Finish, heavy greater excursion, fasten a vessel (p) COn$trUCilOn. LIST PRICE to the ring, and a funnel (y) to the vessel. The incoming sound will be carried On Sale at Leading Dealers. Write for Complete Literature to the diaphragm. ROCKBAR CORPORATION 211 East 37th Street. New York 16, N.Y. If one places the Anvil-forming appendage between the teeth he will pos-

56 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com sibly be able to perceive sound. At the "Strange Facts About the Behavior of very least, by looking sharply, he will be Sound": able to see the movement of the. diaphragm and the action of the hammer If one takes a large jug which has on the anvil. been rinsed out with wine and drops a piece of lighted paper into it a fantastic Reverberation and Damping and awful sound is said to result. The principle of the anechoic chambc; The phenomenon referred to is that appears in this analysis. of a Helmholtz resonator responding to stimulation by a wide frequency spec- There are various ways by which a trum of noise, and emphasizing those body can be made to lose its sound: 1) lie in when thrust under water, 2) when sur- sounds which the frequency range rounded by soft and absorbent mate- of enclosure resonance. Had Ringel- Fig. 5. A military horn supposed to have been rial . Cloth wrapped around clavi- mann been more of a scientist and less chord strings, for example, will kill the used by the Roman army to summon troops. of a Scholastic he would have done that sound. which seems, to the modern mind, High humidity and rain deaden sound; have easily determined for himself the clearly called for -he would have per- also heavy tapestries on the wall. Inside accuracy of a claim. For example, under formed the experiment. buildings, too, it is difficult to understand a lecturer or hear music well when the auditorium is full of people. Sound waves are absorbed and attenuated by the presence of people and their clothing. It is possible to drape an auditorium From with wool or straw to such a degree that the human voice can scarcely be Station Break heard. This is essentially the reason why the sound of bells is muffled during a to Feature... heavy snow- storm. It is not so much that the sound of the bells is reduced by virtue the NEW of their being covered with snow as it is the fact that the roofs and streets are carpeted with snow. Normally, the sound would be reflected from the otherwise bare surfaces.

is doing a whale of a job every day! Fig. 4. Artificial hearing mechanism. The combination of horn and diaphragm is prophetic of 19th century phonograph design. "BALANCED" Military Applications of Sound TV TRIPOD During wars, advance patrols report mounted on that they can hear 3 -wheel the sound of cavalry portable We THREW THE book away and engineered a 1,000 over paces away, if they dig a little brand new "BALANCED" Tripod for every photo- pit and put their ears close to the earth. collapsible The fabulous dolly graphic and video need. The result-a revela- horn of Alexander the Illustrated. Great, made by Aristotle, was able to tion in effortless operation, super- smooth tilt project a blast of sound 60,000 paces and 360° pan action. (about 35 miles). It was used to summon the Army and took 60 men to blow it. PERFECT BALANCE prevents mishap if the lock Another description of the horn says it lever is not applied. Quick release pan handle was 5 cubits (6.8 ft.) across and could locks into desired position. Mechanism is en- be heard 12% miles away. (See Fig. 5) closed, rustproof, needs no lubrication. Ten- Legal and Humane Considerations sion adjustment for Camera Man's preference. Built -in spirit level. Telescoping extension pan When transferring a swarm of bees through a populated area one must give handle. We defy you to get anything but the ample warning by banging on a brass smoothest, most efficient operation out of this kettle. tripod beauty. Nowadays, unless one gives ample warning when throwing something from an upper window out into the street, he WE DESIGN and manufacture Lens may be sued for damages. WE CALIBRATE LENSES Precision "T" STOP CALIBRA- TION of all type lenses, any focal length. Our method is Mounts and camera equipment for From which we may conclude that approved by Motion Picture Industry and Standard Com- 16mm - 35mm and TV cameras. courtesy and grace were not unknown mittee of SMPTE. Lenses coated for photography. in 1693. Special TV coating. FRANK C. ZUCKER Legend and Hearsay WE RENT AND SERVICE GAIllERR EQUIPmEf1TCD. Ringelmann's thesis reflects a culture CAMERAS " MOVIOLAS ` 1600 in which the scientific attitude was just BROROWAY 11EW 9ORH CITY emerging. It contains much perceptive DOLLIES Complete line IF YOU WORK WITH FILM .. . analysis and insight, but the author also of 35mm and 16mm equipment available for rental. It will pay you to get to know us. retains some of the disdain of Scholas- The country's foremost MITCHELL: Standard, Hi- Speed, BNC, NC, 16mm. Bell s ticism for experimental verification, and professionals depend upon our he is often content to cite unchecked HOWELL: Standard, Shiftover, [yernos. MAURER: 16mm portable, versatile, adaptable legend or hearsay, even when he could Cameras. ARRIFLEX. MOVIOLA: Editing machines, Synchronisers. equipment.

AUDIO ENGINEERING MARCH, 1953 57

www.americanradiohistory.com WHY PAY RENT on your echo chamber? FIRST INVENTOR Goodfriend Facilities -Audio Reverberation Unit [from page 40] now made exclusively in improved form by ventor to discoveries disclosed in his application to which he had not made Audio Instrument Co., Inc. claim and that such discoveries were as Simulates reverberation of a consequence, available to others. a room of any size, using "The question is, therefore, squarely presented," said a magnetic tape loop sys- that court, "whether tem with FIVE HEADS on the issue of prior invention it is the (Model 40) or SEVEN claims or the disclosure which counts. On principle it would seem that the HEADS (Model 42). claims were the place to look for the AN ECHO CHAMBER ON AN 8.3í4't x 16" PANEL Switching heads produces invention. The disclosure, so far as it Compact: Single 8 % "x 19" paneL various special effects, as is only a description of the machine, Variable equalization: Built -in, for special effects. well as natural reverbera- process or composition, is certainly not Reverberation adjustable. time: Continuously tion. the invention proper. It does not tell No pressure pads: Better tape motion, reduced head wear. which of the various elements disclosed Delivery time: Six weeks. the patentee selects as the combination INSTRUMENT which it will be profitable to follow. INC "Without some such selection the Model 40: v lde1.4. V COMPANY art $985.00 V is left without cue for omission and must OepI 1 3 3 WEST 14th STREET N Y 1I.N Y Pays for it.clf in ; to S months. reproduce the whole disclosure in all its details. The claims alone give any scope to the invention and some scope in essential to its value. It would seem that the 'invention' must lie in the act of selecting out of the possible combinations which will read upon the disclo- Authoritative and sure such as are new and useful. "Therefore, at least presumptively, the 'invention' must be found in the Enlightening ... claims and in the claims alone. If so, when the issue arises of prior invention between two persons, whether it be on interference or when raised by an in- fringer, it should be decided only by a Acknowledged the Leading Publication comparison of the claims, i.e., of that in the Field part of the patent or application which of Sound Reproduction sets out what combinations of the elements disclosed the applicant says are If you are novice, hobbyist, experimenter, or engineer... if you his new and useful contributions to the are a lover of music art." ... and in pursuit of sound, undistorted The discoverers of this process for . . . Audio Engineering will be your faithful, reliable corn - acetylene welding appealed and the de- panion all the way. You will find no more pleasureable and cision of the Federal District Court was stimulating reading affirmed by the Federal Circuit Court than there is in AE; absorbingly interest- of Appeals, which stated, ing material, valuable and authentic data, workable detailed in- "Thus the question is narrowed to structions ... all comprehensively and yet practically presented. this, does the 'first inventor' of the fourth defense signify one who describes patentable matter or one who both de- "What to Do" and "How to Do" will guide your every move scribes and claims it. The question may through this thrilling experience we call Audio. be put thus, is mere disclosure (confi- dentially made to the Commissioner of Each new issue brings New Ideas, New Slants, and Latest Devel- Patents) and no more, in itself, sufficient evidence of invention? We think opments ... month in and month out ... twelve times a year. that it is not, for the reason that in the BE SURE to get your copies REGULARLY. absence of an appropriate claim there is no evidence of the perfection of the mental concept which constitutes this a the invention. 1 intellectually part of "We hold that a 'first inventor' within AUDIO MAIL this ENGINEERING the meaning of that phrase as used in P. O. Box 629. Mineola, N. Y. the fourth defense, must be a person Enclosed is who perfects his invention. No inven- Coupon ] Check C Money Order ter $ Please send a opy of each now issue of Audio Engineering fee the neat tion can be intellectually perfected un- [¡ 12 months; G 21 months to: less is NOW Please Print it thought out and concluded and Nome the only evidence of such perfected invention ordinarily derivable from any Address patent is a union of disclosure and City Zeno State claim." Subscription Price: C U.£A.. and Pen American Union: 1 year . the $3.00 2 years $3.00. Other countries: 1 year..$4.00 2 years..$7.00. When appeal from this decision came before the United States Supreme Court a year and a half later the court

58 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com 4

reversed the decision of the two lower courts on the opinion of Justice Holmes who established at that time the definition of 'first inventor' that is now made a provision of the patent statute itself. It is not disputed that the applica- Vemeadioptai Sciage? tion gave a complete and adequate description of the thing patented but did not claim it. The patent law authorizes RESEARCH a person who has invented an improvement like the present, 'not known or DEVELOPMENT used by others in this country before invention' to obtain a patent for it.... SERVICE The fundamental rule, we repeat, is that on the patentee must be the first inventor." REFERENCES Detrola Radio & Television Corp. v. Hazel- Diamond` Sapphenoí& Sapphire° tine Corp., 117 Fed. 2d 238: 313 U.S. 259 Hazeltine Corp. v. Abrams, 7 F. S. 908; for 79 Fed. 2d 329 Davis -Bournonville Co. v. Alexander Mil- Acetate Disc - Sapphire Cutters burn Co., 297 Fed. 846; 1 Fed. 2d 227; 270 U.S. 390 Magnetic Film - Diamond Scribers

COLUMBIA "360" Magnetic Tape - Sapphenoid Guides {frone page 29] To Your Specifications tances and locations. The resultant curves were integrated and then aver- Veacoaatic ,eC'aeonatanv aged to yield the one illustrated. Very S,nco 1553 close correlation can be found between the sound characteristic thus derived P. 0. Box "P" Phone STate 4 -0881 and the actual performance of the player in the home. Encino, California The amplifier has been designed to give adequate performance for a maximum power output of about two watts, as shown in the distortion curves, Figs. S O N T Y P E 6 and 7. The amplifier frequency response has been shaped so that when combined with the other components of the system, the over -all sound pressure qeatk/'t diagram is the desired one. Figure 8 shows the frequency response of the pickup by itself. AMPLIFIER KIT During the development of the Colum- bia "360" in the CBS Laboratories Divi- FEATURES sion we had to rely on the support and Practically distantness. Harm,mc and letermaduI*Ian distortion nth less than /ea hall 111ió at 5 watts. inspiration of many. In particular, the Frequecy response f- I dh Irem 11 cycles to IA kilocycles. writer is indebted to Thomas Broderick, Altec Lensiq PEERLESS or ACROSOUND Transformers available. Richard Mahler and René Snepvangers First Willmar type Ampller suppled with molding preamplber. for their wholehearted cooperation When selecting an amplifier for the heart of a fine high- and ` fidelity audio system, investigate the outstanding advantages many useful suggestions. offered by the Heathkit Williamson type Amplifier. Here is an amplifier that meets every high -fidelity audio require-

. ment and makes listening to recorded music a thrilling new experience through naturally clear, lifelike reproduction of sound at all tonal levels. Wide acceptance of the Heathkit

.. Williamson type Amplifier by the most critical purchasers clearly demonstrates that high -fidelity can be coupled with EIIi1' II9 low cost. For factual information regarding the Heathkit Ill .tarh ' Williamson type Amplifier. consult "CONSUMERS RE- SEARCH ANNUAL CUMULATIVE BULLETIN 1952 -53." "'1"'IIIÏ4IIIP,Alll This outstanding amplifier is offered with the optional choice of the ACROSOUND output transformer or the PEER- LESS output transformer. ACROSOUND features ULTRA. .SIIIIICIIlI i10III LINEAR circuitry, which is the exclusive development of the PRICES OF VARIOUS COMBINATIONS Acro Products Company and provides a.greater margin of W.2 Amplifier Kit Ilnel. Main Amplifler Ilill 111 reserve power efficiency and increases power output. PEER- .. dh Peerless Output Transform- III EI . Power Supply and WA -PI LESS features additional primary taps to permit the optional Preamplifier Kit) Shipping f 6950A choice of either the extended power circuitry. now enjoying Weight 39 lbs. Shipped express n iy. current popularity, or all of the advantages of the original 1.10-2M Main Williamson type circuit. h Peerless Output erAmplifl. The construction manual has been simplified to the point m,, rower Supply) Shipping $ 15 \V..ight 29 Iba. Shipped express where even the complete novice can successfully construct ::IY. T without difficulty. Write for a tree catalogue Fig. 8. Typical response plotted against the the amplifier W.3 Amplifier Kit lined. Main Amplifier electrical curve of Columbia 103 test record. containing complete specifications and schematics of the ..VIh Acrosound Output Trana- Heathkit Williamson type Amplifier. Power Supply and WA- hteampllfler Kit) Shipping Height 39 lb, Shipped press $ REEVES APPOINTS NEELY W -3M Amplifier Kit tlnrl. Main Amplifier foith Aerosound Output Trans. rmer and Power Supply) Ship- Ii Products of Reeves Soundcraft Corpo- ping Weight 29 lbs, Shipped f e presa only. ration, New York, will be distributed to HEATH COMPANY WA -Pa Preamplifier Nit only. Shipping Weight 7 lbs. Shipped express the electronics industry in the Southwest BENTON HARBOR 25, MICH. ur parcel post. by Neely Enterprises, Inc., Los Angeles, $1g>s effective at once, according to Frank B. Rogers, Jr., Reeves vice -president.

AUDIO ENGINEERING MARCH, 1953 59

www.americanradiohistory.com MAGNETIC PICKUPS [from page 20] from 10 to 50 iii in the input wiring, cutoff frequencies are shown in Fig. 5, plug and socket, and switch (if used) in for each of the four pickups calculated. no. the preamplifier. For any cartridge at any desired cutoff type From all this, it is apparent that a frequency the values of RL and C may total shunt capacitance of at least 100 be read directly from the left -hand specs. p.p.f is assured for any installation. A scales. long run of shielded wire between the Figures 6 to 9 inclusive show the ef- turntable and preamplifier with the use fect of capacitance only on each of the of high -mu triode tubes can easily bring four pickups. A wide range of values circuit was used, to cover the range from the total capacitance 1000 p.p,f to or 5000 to 20,000 cps in each Nearly case. From t' diagram more. all practical installations all of these curves it will easily be seen will fall within these limits. Since most that significant changes in high -fre- values of RL will fall between 1000 and quency response can occur as a result 200.000 ohms, a working range of RLC of the capacitance across the pickup ter- will lie between 1 x 10' and 2 x 10. minals.

TABLE II Miller- Effect Capacitance of Input Tubes Tube Type C: G:. Amplification Total Capacitance-µµf 6SN7 (6J5) 3.0 4.0 15 63 6SL7 3.4 2.8 52 159 6517 7.0 .005 100 7.5 6AU6 5.5 .0035 100 6.5 6C4 1.8 1.6 15 25 6SC7 2.2 2.0 40 83

Calculation of Frequency Response TABLE Ill Equation (1) was reduced to a series of graphs, which were then used to cal- Capacitance of Various Shielded Wires culate the electrical response of the four Wire Type Capacitance-out per foot pickups under various load conditions. Shielded hook -up wire 55 -70 The response calculations were divided .140 0. D. Microphone into the following classifications: cable 40 .200 0. D. Microphone (1) RL= 00, C varied. cable 25 (2) C fixed, RL varied. Heavy duty Microphone (3) RL and C chosen to provide the cable 33 sharpest cutoff at certain frequencies. It will be observed that L and C form The amount of rise at the peak de- Triad Power Transformers -like a low -pass constant -K filter section, and pends, of course, on the Q of the circuit. other Triad transformers -have the that it is possible to choose values of C The various pickups differ somewhat essential information right where in that respect. Furthermore, the loca- and RL to satisfy the relationships : you want it -on the decal. tion of the peak depends on the induct- It simplifies installation- speeds ance of the pickup coil, for a given ca- afe and C servicing -makes reordering easy. =afcRL (3) pacitance. In general, therefore, the Whether used for replacement, higher impedance (hence higher induct- industrial applications, PA amplifiers The values of R1. and C for various ance) pickups are more sensitive to or amateur gear, they offer small size, maximum efficiency, low temperature rise and low cost. Also, 0.1 0.1 they are "Climatite" treated, CLARRST6N--- == auoaR --- both coil and core, _ for protection 0760.. Nç L 720.. 6__m R630.... against moisture and for elimination R1660.... Z_,_- ti_ IIMM PICKERING of lamination chatter. Laminations LW 4 E. II - are painted to - prevent rust. Copper íLis7o«..II- C ..16 ñwoo«.. straps are used for static shields, 01 I, 01 oo .i_mC::'.'. I..=:=E grounded to case and core. 01.1M111IMM, 11111MrMMwc:..:::JI Leads are color coded, UL approved. IF,=tellIN 'it7B1 Final tests include 11 checking for proper : operation. Cases are finished in durable, attractive 001 001 Iaii 1 grey baked enamel. "JI!: __ \ Write for Catalog TR-52F 1,01M11/aIM;...... mone. I1 MIMI \ \ IIIIIMIIIIII11111III lR 00011000 1111111111 10000 II 10000 20000 1000 20000 FREQUENCY FREQUENCY -...

4055 Redwood Ave. Venice, Calif. Fig. 5. Values of R,. and C for various cutoff frequencies for the four pickups.

60 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com shunt capacitance effects than are the lower impedance units. In the very- high- impedance units, particular care should be taken to re- ß Built for the duce shunt capacitance, since even 100 or 200 µµf will have a significant effect on the response above 10,000 cps. BROADCASTER The addition of a shunt resistance w 1 makes it possible to flatten out the reso- b nance peak, but it is not possible to ob- Here at last is a magnetic tape recorder specifically designed to meet all the requirements of broadcast, recording and industrial engineers -the Concertone NWR -1.

The Concertone NWR -1 incorporates ad- vances in engineering and performance +10 ii 100VVf found in no other tape recorder: Automatic /91 brake system needs no adjustment. Direct _i_/,r1't _. drive from dual speed hysteresis synchron- 00 ous motor Accommodates up to 5 heads °< Suitable for rack panel installation or ®1 portable cases May be serviced during '. operation Full pushbutton remote control n, Accepts up to NAB size reels without ',' adapters Metering of input, output and . bias levels. AUDAK RL. o

20000 foo 10000 Write for Bulletin 300 FREQUENCY - cps 1111111\ Manufactured by

Fig. 6. Response of Audak L -6 pickup with Berlant Associates various shunt capacitances and a resistive 1917 W. Jefferson Blvd . Los Angeles 16, Calif. load of tain any significant response above the cutoff frequency. l> Figures 10, 11, 12 and 13 show the effects of adding resistance in parallel with the shunt capacitance. It is apparent that a value of resistance can be found to give substantially flat response out to the cutoff frequency, but the upper frequency limit is definitely fixed by the product of coil inductance and shunt capacitance. When the values of RL and C satisfy the relationships expressed by Eqs. (3) and plotted in Fig. 5, a low -pass con stant -K filter network results. To indi- ANNOUNCES cate the kind of result to he expected with each of the four pickups, Fig. 14 Grand Opening New York's Largest Audio Center

.0002 pf 650 Sixth Avenue +10 0001pf FEATURING

NOT 1 ... NOT 2 ... BUT 3 o _ á ( rg Al Complete SOUND STUDIOS > -10 * Conveniently located for easy access from a any part of Metropolitan New York to help 4. * Staffed qualified personnel á solve your u * The most complete display of all finest -2 audio equipment CARTR DOE makes of O.E. * Visit us today and see why Sun Radio sets the standards for the audio industry Ru.m * Get your free copy of Sun's 1953 Audio I Equipment handbook. 100 of the most 20000 any music lover could have 1000 10000 valuable pages

FREQUENCY - cps & E L E C T R O N I C S CO.

Fig. 7. Response of GE RPX -050 pickup with 650 Sixth Ave. at corner of 20th St., New York, N. Y. ORegon 5 -8600 Open Dily & Saturday 8:30 -6:00 various shunt capacitances. R,.= .

AUDIO ENGINEERING MARCH, 1953 61

www.americanradiohistory.com .001Yf 200 OOV 100rvf y 200rr1 ,SVf . i: , +10 +10 w è. JAIMIG2 o : b1. 100r1d W.,s bl I , 1II\Aii III1g-

PICKERING I120M -

RL Im The Famous Baruch -Lang I -30 s000o I HIGH FIDELITY 1000 10000 CLARKSTAN Ill SPEAKER SYSTEM FREQUENCY- cps RL o I 4 SPECIALLY DESIGNED 30000 .., 10000 SPEAKERS, COMPLETE . . WITH CABINET Fig. 8. Response of Pickering D120M pickup FREQUENCY- epa with various shunt capacitances. R1,= r. $29.9áa, Hi -FI { Model 501 -- ßíw Fig. 9. Response of Clarkston pickup with Compact.. highfidelity corner speaker system, developed was prepared, using values selected various shunt capacitances. R. = 00 at the famous Mass. Institute of Technology. Baruch- from Fig. 5 for a cutoff frequency of Lang principals approach acoustical qualities of larger the rate of attenuation above cutoff is units costing four times this low price. Small space be expected, the 5000 cps. As might very close to 12 db per octave. requirements, high output and wide dispersion angle. sharpness of cutoff varies from unit to make it perfect for low cost, high Adel ity music systems In order to check the equations which In homes. public buildings. restaurants. schools. Con- unit according to the Q of the coil. This were used to obtain the foregoing re- nects easily to phono systems. FM -AM radios. TV. Q cannot completely be represented by Response: 40 to 12.000 cps at plus or minus 3 db. sponse curves, actual measurements 13" high. 19" wide. 9'," deep Wt. ten lbs. 4 ohms impedance. Rwhere L is the coil inductance and were made by two methods: the pickups were tested on a standard frequency Brilliant New Hi- Fidelity! R the coil and lead resistance. The ac- record, and they were also checked by PILOT FM -AM TUNER tual Q depends on the a.c. losses (eddy the simulated- signal method. The meas- Self -contained p currents, hysteresis, etc. in the soft -iron urements made with the frequency rec- _' ply. With tout magnetic structures in the pickup) as ord gave close agreement up to 10,000 flat position. audio I'- well as the d.c. resistances. However, it quency response Ls w cps, and increasing spread, of a random 1:11:011 p111, min* 2 db. M... was found that in devices of the type nature, above that frequency. This is to din ' ' ....I audio output being discussed here, the discrepancy 6 -E2. 1 be expected because of the high prob- is O $99Á5P between calculated and measured re- able error in this method of measure- PILOTONE AMPLIFIER Model AA902 $42.50 sponse was less than the probable error ment discussed earlier. PILOTONE AMPLIFIER Model AA901 399.50 of measurement. PILOTONE PREAMPLIFIER Model PA911 $29.95 The second method gave complete To indicate what can be done with agreement between measured and cal- The Last Word In High Fidelity the cut -off filter effect, a single pickup culated results. The circuit of Fig. 16 BROOK AMPLIFIERS was provided with four different sets of was used. Low mu triodes for 12A4 terminating R-C combinations selected be,t tonal quality. Re- 10 W. from Fig. 5; Fig. 15 shows the results Conclusion mote control pre -amp amp i -. has inputs for tuner, pro -amp for 3000 -, 5000 -, 7000-, and 10,000 -cps It is evident that the load impedance TV and phono; ore t, cutoff frequencies. It will be seen that across the terminals of a magnetic pho- single chassis units. 8 ;222 position stepped bass nograph pickup will have a great effect and treble control dr- -` cults. Frequency response: 15 to 30,000 _j cycles.

1 i I I I I l l CLARKSTAN 1 G. E. Variable Reluctance AUDAK L -8 +10 - WITH 002 CAPACITANCE CARTRIDGES 1111 AI`: GE RPX -050 dual reversible sapphire stylus 8.37 +10 (:E RPX -051 Same as RPX 050 (less stylus) 5.28 o __ GE SPX -052 Combination diamond and sapphire stylos 23.37 ek \, GE RPX -040 with .003 sapphire 5.97 --_-_-Aa1 GE RPX -041 with .001 sapphire 5.97 GE RPX -0422 (less stylus) 4.35 ,, 10 GE RPX -046 Professional type (less stylus) 6.87 GE HI'X 047 Itroadrast type (less stylist 9.27

ACRO TRANSFORMERS io R 20 All Models fully potted TO -300 for ultra linear 324.75 N RE IISTI E TO -290 15.75 2 100000 OHMS .... TO.270 11.75 1 NO RES STANCE TO-310 .... 18.75 TO -260 11.75 2 50000 OHMS -30 -3 50000 OHMS TO -380 .... 14.50 TO -250 11.75 - 3.20000 OHMS 4 20000 OHMS Address Orders To Dept. AE 3 4 +10000 OHMS 5 10000 OHMS Write For FREE Booklet "Hi -Fi Magic" 20000 I 1000 '10000 20000 1000 10000 WHOLESALE FREQUENCY - cps FREQUENCY cp RADIO PARTS CO., Inc. 311 W. Baltimore SP. Fig. 10. Response of Audak L -6 pickup with Fig. 11. Response of Clarkston pickup with BALTIMORE 1, MD. shunt capacitance of .002 µf and various load shunt capacitance of .002 µf and various load resistances. resistances.

62 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com G.E. G.E. CARTRIDGE For as little as $20 - CUTOFF FILTERS

+10 and no more than $120, 2 your Hi -Fi system 0 . Ai/ 1`II INIO can include the - 10 4 T _ - in 2 100000 OHMS _ 3 50000 OHMS - 20 II\ 1 3KC 9000 .006 4 200000HMS' 2 SKC 15000 .0022 - 5 10000 OHMS. EXPONENTIAL - 3 7KC 21000 .0011 1 I I 4 10KC 29000 .00054 1000 10000 Acoustical Labyrinth 20000 1000 10000 FREQUENCY -spc FREQUENCY - cps

Fig. 12. Response of GE RPX -050 pickup with Fig. 15. low -pass effect shunt capacitance of .002 Itf and various load Curves showing filter RPX -050 pickup when resistances. on response of GE shunted with capacitances and resistances indicated.

PICKERING on the frequency response of the device. This effect can be accurately calculated pickup of coil 1.10 for a given known resist- AA1 ance and inductance. A resistive termination causes a general drop in output at all frequencies, the loss increasing at o high frequencies. A capacitive termina- -'á tion causes a peak at a frequency determined by the LC product, of a magni- - 10 tude depending on the Q of the circuit. R A combination of resistance and capaci- -1 NO RESISTANCE 2 30000 OHMS ii tance will modify the peak, and at one - 20 -3 115000 'OHMS I- specific set of values for each case will 4 5000 'OHM'S constitute a constant -K low -pass filter. er mid -frequency res ònse. 5 3000 OHMS When the resistive shunt has a low No more "Looms- and "thc.mps" of I I I value compared to the capacitive react- ordinary enclosures. Your boss re- 1000 10000 ance, the effect approaches that obtained sponse eoctended downward an oc- FREQUENCY- cep with resistance termination alone. tave.That's al yours IF your p esent The foregoing information can be speaker is a highfidelity coa:cìcI type used to guard against unwanted modifi- and IF you anclose it in the superb Fig. 13. Response of Pickering D12OM pickup cations of the pickup frequency re- Acoustical labyrinth. For complete with shunt capacitance of .005 ttf and vari- sponse, to determine the highest usable technical de'ails, see your deder or ous load resistances. frequency obtainable under a given set of conditions, to compensate for frequency effects in other parts of the system, and to reduce noise from records by using the low -pass filter effect. LABYRINTH AND CABINET, 11ess eMe.,... speaker) in mahogany or blonds oak, 6120

KIT ONLY RL -4.35, to assemble your own Labyrinth with your own speaker $ 2Ó

17 -inch Coaxial Fig. 16. Connection of equipment to obtain Speaker. $49.95 5KC CUTOFF response curves shown. Values observed check R, C with those obtained from frequency records. -- CLARKSTAN 23000 .001401 15 -inch Coaxial ----- AUDAK 25000 .0013p1- Speaker. $179.95 PICKERING 9700 .00670 REK -O -KUT FIRE -s- G E. 15000 .0022p1-

I I l l 11111 Serious damage by fire was suffered by 20000 1000 00 the Rek -O-Kut Company, manufacturer of FREQUENCY - cps precision turntables, Long Island City, STROMBERG- CARLSON N. Y. on the night of January 31. Although production was entirely disrupted for a Sound Division Fig. 14. Curves showing 5000 -cps cutoff with short time, the plant was back in opera- the four pickups when shunted by resistors tion within a matter of days, and is now 1219 1.1.11 FORD :13t.. Iö11:11F:±1 1:II 3. \.1. and capacitors shown in the legend. functioning on a virtually normal schedule.

AUDIO ENGINEERING MARCH, 1953 63

www.americanradiohistory.com AMPERITE THEATER SOUND Studio Microphones from page 31 Et P.A. Prices Design of the Main Case The surest way to cut and assemble Ideal fo- the sections of the wood cabinet without ItOADCISTIN6 mistakes is to make a plan drawing of IICU]INi its assembly to scale, similar to Fig. 7 or 8. This is especially if IIBLIE AIDIESS true the plywood is of different thicknesses. In 'Tie uhietc in micro- plonc qu31,y," says the cabinets we constructed we used %- Ewan 2nlirq, round in. plywood throughout, but the front engines of -he Hotel of the cabinet, Now kskor. sides, top, and bottom could be made 5ho r. rilh into the of thicker plywood if it Strike r ew ATpe rite Micro- is on hand. All pieces must be at least ph sne-c r :ford2 feel %-in. thick, however. away- -.pottudion is Figure &Ways p.1ct. 9 shows the metal horn at- back No. ,Nectod by Models tached to the front by wood screws but ory clisotc cnuiions. this was our first assembly. In later SusonHe! with- r281.3 -200 ohms t. models, the fin -like Hold ereee' kn scking 2BNG -Hi -imp. separator pieces pro- around." ject at right angles from the center of List $4.00 each side of the sheet metal horn, to "Kortok" Mikes act as struts between partitions, and Model SKH, list $12.00 they are slotted across one side to let Model KKH, list $18.00 the 3 /16 -in. truss rods pass through them. These pieces must be shaped to Off.r, Introductory fairly well match the surfaces they are Write for Special Special' 4-paye illustrated to push against, and to obtain a snug Offer: and fit so that partitions will not be sprung out of position as truss rods are tightened. AMPER /TE Gmpany lnc. 561 BROACWAY NEW YORK 12. N. Y. A truss rod passes from the side of Corrado. Atlas Radio Corp., .td., 560 King St. W., Toronto the sheet metal horn to the outside of the cabinet in each of the four directions, Your gifts to the American at the center of the sound passages. After Cancer Society help guard those partitions for folded horn sound passages have been cut and shaped to fit you love. together correctly, these fin -like sepa- Your dollars support research in GROMMES rators must be lined up with the direc- AMPLIFIERS tion of sound and tacked in place with a hundred laboratories and univer- small brads. As the horn partitions are sities ... spread life-saving infor- assembled, a 3 /16 -in. rod (such as steel welding rod) can be threaded through mation ... ease pain and suffering the group to help line up the separators ...provide facilities for treatment while they are tacked in place. Finally each truss rod may be cut to and care of cancer patients. length and threaded on each end. Screw It is a sobering fact that cancer a nut on one end with a thread or so sticking through; clamp the rod in the may strike anyone tomorrow: vise with the nut resting on the jaws; strike back today with a gift to and rivet the end with a ball peen hammer. the American Cancer Society. Model 50 PG This end is used at the outside of .....,...,t ..a...__.....r.: the cabinet with a large washer to keep You may mail it, simply ad- :..:PP::+..a,.. the nut from seating into the wood with .b.,a..m l'.0 1>.40r.. the vibrations. The other nut is screwed dressed CANCER, do your local on the end which sticks into the sheet post office. metal horn, with a good lock washer to keep it from working loose. Allow plenty of thread on this end for tightening. In installing Model an 8 -in. speaker frame on the larger magnet an additional 16- 215BA ga. metal flange can be included in the assembly, as shown in Fig. 7, to form 15 Wort ' a tie or hub for the partitions of the sound chamber. This member ALL TRIODE seals off BASIC AMPLIFIER the passage of sound to the rear and Retpon.e 1 200 00,900 CPI. P.I.a pawar 21 wan.. Onlortiom gives a more direct support American ate and .2% for the alarm heavy magnet. With our first woofer botk Wen Imp- 2 dirM touP4d stapes, $ 0 Cancer tahode tolla..n. drv.n. 0 0 5 we used a wooden collar, fabricated by glueing two layers of -in. plywood Society WRITE FOR CATALOG together, as shown in Fig. 8. One layer was given % -in. PRECISION ELECTRONICS, slots to let a 3 /16 -in. &to, Inc. tie rod pass through on each side 9.01 of the King Avenue, Franklin Park, 111. speaker magnet.

64 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com 0000000000000 o Where the metal horn fits through Before tightening the truss rod nuts o the front panel and where the partitions in the metal horn, on the final assembly, o RADIO -ELECTRONICS fit to the wooden collar around twist a turn of small wire under each 00 o were A Preview of Progress the speaker, a thin layer of plastic (non- nut and allow the two ends to reach hardening) putty was applied between out the front like hairpins. Then take I.R.E. CONVENTION surfaces. This was to seal from passage an old gauze or lace curtain and wad it 00000000.0000 it loosely in the horn to of air and to prevent any spurious vi- up and pack RADIO ENGINEERING SHOW brations at joints. fill it almost to the mouth. Place a piece No. 8 wood screws, of different of light hardware cloth over this curtain lengths, were used in our first cabinet. and secure in place with these hair pins. 405 Lengths were chosen so that 1 in. or If the hardware cloth is not light and more of thread was seated in the holding pliable, its ends may receive vibrations member and they were spaced 1/ in. from touching the metal horn. EXHIBITS apart in short runs and 2/ or 3 in. The purpose of this curtain wad is along the main sides. A small hole was twofold. Naturally, the direct radiated WALD ORF -A S70RIA'NOTEL drilled to guide each screw and prevent sound is much more effective than the GRANO CENTRAL PALACE splitting of edges of panels. Then the lower notes which have to traverse the NEW YORK CITY hole through the held piece was enlarged folded horn. So this material acts as a MARCH 23 26 1953 for the shank and countersunk. A bit of mute to cut down the intensity of the floor wax was used to ease each screw emerging notes and provide a distortion - home in its long run. free coupling with the outside air. Thus COME AGAIN - a fair balance can be obtained between Arranging Inner Passages the two horns and further experiment- AUDIO MEN! In computing the sound passage area ing may be resorted to in order to suit Welcome to the Radio Engineer- past the speaker mounting flange, the the needs of the particular speaker and ing Show- cross sectional area between partitions, horn assembly. at A in Fig. 7, is figured and the cir- Don't be too concerned about the cular area of the speaker flange de- looks of the sheet metal horn or other March 23- 26,1953 ducted. It will be seen that the sound features around that part of the cabinet waves have to turn a 90 -deg. angle at because it will have to be covered with at New York City the space marked A before departing some cloth or other finishing. Picture 19 IRE Professional Groups have from this chamber back of the mounting molding was used to form open louvers prepared skillfully organized sym- ring. Thus frequencies of the intermedi- over the horn on our first cabinet. There posia and technical sessions on all ate range are filtered out by acoustical are many ways to dress up this cabinet phases of radio, TV, and electron- resistance before they can cause much to fit in with the surrounding environ- ics. These papers will keep you distortion in the folded horn passages. ment. Do not run any wide molding up up- to-the- minute on the develop- Continuing along the inner sound the edge of the horn opening against ments which are to come in the passages, the cross sectional area at the wall at D, Figs. 7 and 8. Any mold- next few years-for the IRE Con- each change of direction is figured for ing which extends into this opening vention Theme is: doubling every 12 in. in axial length. from thé wall would curtail the annular Since there is no continuous 12 -in. run movement of the lowest notes along this in any part of it, this can only be a outer wall. Radio -Electronics rough approximation, by proportions. Like most experimenters, we have Remember to allow for the same degree never gotten around to finishing our "A Preview of expansion as the sound bends around cabinet because we are too busy on of Progress" because it may the end of partitions other projects. Louvers should not be The colorful Annual Meeting on travel four or five inches axially in these used over the tweeter and any cloth used Monday at 10 (opening morn- bends. Leaving the sound chamber at A, over its opening should be of fairly the low notes pass toward the front of ing) will feature the "Founders' loose weave and hard, wiry thread, Award ". Social Events include the the cabinet and are bent back at B to preferably plastic. pass rearward along the top and bottom "Get Together Cocktail Party" Both the tweeter and the center horn Monday, and the Annual Banquet panels to C. be mounted must flush with the front Wednesday, all at the Waldorf Many corner speaker cabinets de- surface of the panel (disregarding pend on the walls of the room to form louvers which extend beyond). The Astoria Hotel. the final folded passage, but this design reason for this is, of course, to avoid 405 Exhibitors are using 58,680 uses complete side panels with the truss any discontinuities in in Pieces of %- the sound path square feet entire four floors rods terminating them. where the horn joins the open air. -the in. hair felt were glued along the out- Sounds like a lot of work, of Grand Central Palace, to gist. of to doesn't it? side these panels prevent their It has taken years of struggling to you a "Preview of Progress" in making vibrating contact with walls of achieve this ideal and the real the apparatus, components and Rubber feet were installed on listening the room. satisfaction for a true music fanatic. instruments of Radio-Electronics. the bottom. Thus, there is practically Let's put it this way: A sextet of saxo- Registration: IRE Members $1.00 no sound transmission through the room phones of different ranges can imitate Non -Members $3.00. Register at walls at normal operating levels. the brass choir, but the comparison in inserts of sheet metal were Grand Central Palace, 47th & Lex- Curved texture is about the same as comparing bolted to the side walls and center sep- ington Avenue, or The Waldorf help last an ordinary 12- or 15 -in. resonator - Astoria Hotel, 49th & Lexington arator to the sound around the boxed speaker with our system -except bend at C and prevent possible distor- muddier Avenue, New York City. tion in this large chamber which sur- that the saxophones are a little rounds the magnet. This sheet metal than the box speaker. series, we may be any gauge from 28 to 22, for In the final article of this THE INSTITUTE OF go with easy shaping. Use lock washers on all will discuss the controls that RADIO ENGINEERS bolts, which are 8 -32 machine screws the dividing network. in most locations. [To be concluded]

AUDIO ENGINEERING MARCH, 1953 65

www.americanradiohistory.com It's no trick! HANDBOOK [frotn page 34] No talent or training needed to splice any

. which type of safety film, - - is decoupled and remains at rest A typical inexpensive "console" speaker forever, the new, elec- during purely treble stimulation. of 12 -inch diameter uses a 6.8 oz. Alnico Analysis of the tric "butt- welded" mir- circuit of (B) in Fig. V slug. Quality 12 -or 15 -inch speakers 9 -5, one of the possible variations of the acle device does it may use Alnico magnets two -cone, single- voice -coil design, is V of several AUTOMATICALLY! very similar, and is left to the reader pounds. as an exercise in using dynamical analo- The gap is made as small as can be Prestoseal splices magnetic gies. afforded without danger of rubbing. The Distribution of mass at voice coil must therefore not warp film permanently different fre- easily, and the spider must quencies may also be achieved by the have maxi- in 10 seconds! use of separate speakers. mum radial rigidity to keep the coil in The frequency the narrow path prepared spectrum is divided into two or three for it. parts and a speaker with appropriate The Electrical System of the Speaker mechanical characteristics is assigned to cover each band. These speakers may Some years ago high -impedance be mounted on the same axis, which speaker voice coils, connected directly gives the assembly the title of coaxial into the output a. c. plate circuit, were speaker. used. High -impedance voice coils have one great advantage, in that the need The Magnetic System of the Speaker for a matching output transformer -the After the suspended mechanical sys- most costly and critical part of an audio tem of the speaker has been made suit- amplifier -is eliminated. The use of this able, to a greater or lesser degree, for type of voice coil was abandoned, however, for the greater convenience of . r forced vibration over a given replasticized! band of Eliminates dis- low-impedance tortion, drying out, no overlap or frequencies, an electro- magnetic system coils, which used fewer double thickness, no cement, for converting the electrical signal into turns and heavier wire. Recently the brushes or scraping. Guarantees mechanical force is required. The fixed high -impedance design has been revived, perfect frame alignment. No lights magnetic field in which the voice coil and new output circuits make possible required. is placed should be as intense as possible. lower requirements for voice-coil im- J Brochure on request The greater the magnetic flux of this pedances. field the more efficient the conversion, The typical modern voice coil has a and the more effective will be electrical rated impedance of from 2 to 16 ohms. PRESTOSEAL ORP. damping. It is also necessary that the The common 5-inch table radio speaker has an impedance of 3 to 4 ohms, 3727 33rd st., Long Island City 1, L.I. field be uniform over the area through and which the voice coil will move, so that large speakers are rated at 8 ohms or a constant relationship can exist be- higher. The d. c. resistance of the wire tween the instantaneous amplitude of the is usually about three -fourths of these EVERYTHING IN AUDIO! signal and the magnetomotive force ap- figures. plied to the voice coil. The value of the rated or nominal HUDSON The usual magnetic structure is of impedance represents the actual electri- RADIO a TELEVISION the CENT. type appearing in Fig. 9 -1, where only cal impedance of the loudspeaker at Largest Selection of ALL Standard Elec- the slug is made about 400 cps and at that frequency tronic of magnetic material. and High -Fidelity Equipment. The field path between the north and only. The effective electrical impedance Ultra-Modern Audio Comparison south pole of the slug is directed by the presented to the amplifier at other fre- Sound Studios U- shaped iron structure and the pole quencies varies considerably. It is LOWEST PRICES FINEST SERVICE piece of mild steel. The low reluctance strongly influenced by what is called of this magnetic circuit, compared to the motional impedance of the speaker, that of air, confines almost all the lines and the electrical inductance of the ' 1953 Newest of force to the metallic path, and the voice coil presents an increased im- NEEke Most Complete voice -coil gap then receives the full pedance to signals of higher frequency. concentration of lines when they must (See Fig. 9-6.) HUDSON CATALOG cross the gap to complete the circuit. If the voice coil were clamped so that Other types of magnet structure are it could not move the speaker would used, but aside from questions of cost have an impedance, at a particular fre- 1M1.,. Over 196 pages . the final merit of the structure is judged quency, referred to as the blocked .ti value -packed with the world's finest Radio, TV by the magnetic flux produced in the impedance. When the voice coil is al- and Electronic Equip- gap, and its uniformity over the path lowed to move in the magnetic field it ment. High -Fidelity and of voice -coil excursion. The strength becomes the armature of an electric PA Sound Equipment - . - Amplifiers, Speakers, Tu- of the magnetic field at the gap is de- generator, and a back electromotive ners, Record Changers, by force is Recorders, Packaged termined the material and weight produced, opposing the input Systems, Custom Furni- of the slug, the degree to which the signal voltage. Effectively, then, it is ture, etc. for Profes- field in confined to the metallic circuit more difficult for the source to send sional and Home In- stallation. and gap by the magnet structure, the current through the voice coil, since size of the gap, and the back e.m.f. must be overcome in ad- Send far saturation limit Your FREE Copy (Dept. D -3) of the steel. dition to the voice coil impedance, and When you attend the IRE SHOW, be sure to visit our Some years ago really powerful the source "sees" an increased imped- uptown Sound Studio, mag- adjoining Radio City . .. only 41 blocks from Grand Central Palace! Open until nets could be produced only by field ance between the speaker terminals. 9 P.M. during show time, March 23-26. coils wound on soft iron cores. With The increase of impedance may also be modern magnetic compounds made of described in terms of Ohm's law ; for iron, aluminum, cobalt, nickel, and a the same signal voltage applied to the HUDSON small amount of copper (Alnico speaker, less current will flow. This is RADIO & V) TELEVISION CORP. the permanent magnet type of slug is illustrated in Fig. 9 -7. able to produce fields of high 48 WEST 48th ST. intensity. The increase is the value of the 212 FULTON ST. Earlier types of Alnico, designated New York N Y by motional impedance. 36, Circle 64060 Ne. York 7, n Y Since in a given lower numbers, produce weaker fields. speaker it is determined by voice -coil

66 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com velocity, it is affected by all the components of the mechanical impedance, and of the acoustic impedance reflected into the speaker mechanical system, that influence this velocity. It is a maximum at speaker resonance, where voice -coil velocity is greatest. The variation in amplifier load indicated in Fig. 9 -6 has a serious effect on performance at different frequencies. Amplifier design which incorporates a very low source impedance, and a mounting which affords good acoustic loading for the cone, will counteract this effect to a large degree. Part II will appear next month.

Afeand Individually tested. No WWFB leaves our works AUTHENTIC without being individually tested. Close limits set on WILLIAMSON PERFORMANCE shunt reactance at 50 c s. Accepted as the most efficient output transformer AMONTHLY SUMMARY of product develop- Series reactance at 5 in the world, and for which there is no U. S. equivalent. ments and price changes of radio elec- Type WWFB ensures the per- Kc d.c. resistances and the Partridge -Williamson tronic-television parts and equipment, s; formance intended by the designer. Covering the full supplied by United Catalog Publishers, Inc., interwindings insulation audio range it has the lowest possible distortion. It is 110 Lafayette Street, New York City, pub- resistances at 2 K.V. now available to all -off the shelf from all good job- lishers of Radio's Master. bers. If in any difficulty write us and mention your job- These RKPORTS will keep you up -date in -to Price bers name -Don't tolerate a substitute -get the trans- this ever -changing industry. They will also built for the job Partridge -Williamson. help you to buy and specify to best advantage. former -the A complete description of most products will AVAILABLE TO ALL be found in the Official Buying Guide, Radio's 26.00 Master- available through local radio parts $ IMMEDIATELY FROM STOCK wholesalers. duty paid Recording Equipment, Speakers, Amplifiers, Needles, Tape, Etc. PARTRIDGE TRANSFORMERS LTD., TOLWORTH, SURREY, ENGLAND ELECTRO- VOICE-increased price an Model 6 -HD diffrac- tion horn to $15.00 net. FAIRCHILD RECORDING EQUIP. -Added Model 650 -C IF YOU ARE MOVING preamplifier at $47.50 . . . Model 651 -B power supply at $51.00 net, and Model 852 -C preamplifier at $47.50 Please notify our Circulation Department at least 5 weeks in advance. The Post net. Decreased price on Model 620 -CL power amplifier addi- to $190.00 net. Office does not forward magazines sent to wrong destinations unless you pay GARRARD SALES -Discontinued multispeed transcription tonal postage, and we can NOT duplicate copies sent to you once. To save your- turntable Model 201 /B5. self, us, and the Post Office a headache, won't you please cooperate? When notify- GENERAL ELECTRIC -Added Model UPX -009, pickup and transcription arm at $9.33 net . . Model ing us, please give your old address and your new address. RPX -051 triple -play variable -reluctance cartridge at Circulation Department $5.28 net, and Model RPX -042 variable -reluctance cartridge at $4.35 net. Discontinued Model RPR -046 RADIO MAGAZINES, INC. broadcast type variable reluctance cartridge. LOWELL MANUFACTURING CO. -Added "The Richmond" Mineola, N. Y. series of wall -type speaker baffes. Decreased pelee on P. 0. Box 629 Model H -24 bi- fidelity decorative grille to $10.50 net. MAGNECORD- Diseontinued Model PT7 -A recorder mechanism for portable, rack or cabinet modela . . . Model for clear, controlled sound in corridors P11-AX, same as Model PT7 -A less ease . . . Model PT7 -CC, console combination. PRECISION ELECTRONICS- Decreased price on Model 100 -BA bask amplifier to $41.25 net, and Model LOWELL Bi- Directional 215 -BA high -fidelity triode amplifier to $99.50 net. i west coast prices slightly higher). SPECIFY Speaker Baffles REEVES SOUNDCRAFT -Added Soundcraft 45- r.p.m. recording disc at $.66 net. MARK SIMPSON MFG. -- Increased prices on No. 52 series ,,f tape recorder, Test Equipment RADIO CITY PRODUCTS -Added Model 345 super vacuum - tube voltmeter at $47.50 net. and Model 8873 TV servishop unit at $139.95 net. Discontinued Model 854

V.T. voltmeter . . . Model 449A pocket multitester, and Models 447BK and 447BPK multitester kits. R.C.A. -Increased price on Model WO -RBA, 5 -In. oscilloscope to $169.50 net. Tubes -Receiving, Television, Special Purpose, etc. GENERAL ELECTRIC -Added germanium diodes 4JAIAI at $1.95 net .. 4JA1A2 at $3.85 net ... 4JAIA3 Corridor speaker installations, in ceiling or walls, give the best at $4.80 net 4JA2A4 at $5.30 net ... 1N81 performance when equipped with Lowell Bi- Directional Speaker Baffles. Sound waves are at $4.35 list and 070 at $2.00 list. Discontinued 0 -10 series of transistors (0 -10, 0 -10A, 0 -1011 and 0 -10C). directed in a concentrated beam along the length of the hall, permitting low level RAYTHEON -Added special purpose tubes CK5870 at $7.00 volume of clear, undistorted sound. Echoes are held to a minimum. Heavily loaded at net ... CK5750 at $3.25 net CK8212 baffle housing reduces feedback, eliminates metallic resonance. Speakers are protected $7.50 net . . . CK8247 at $14.65. net. Also added germanium Junction transistors CK721 at $12.50 net. from dust and mortar. Bi- Directional baffles are easily installed in new or existing con- and CK722 at $7.80 net, struction, available in five series to accommodate 6" to 12" speakers. SYLVANIA -Added TV picture tube 212P4A at $40.00 net ... special purpose tube 6BF7W at $4.45 net. Please write for complete. illustrated installation instructions, specifications and prices. Also added radio receiving tubes: 6T4 at $3.55 list ... 811Q7A at $3.20 list . . . 811K5 at $2.45 list 3030 Laclede Station Rd., . 12B4 at $2.00 list. Discontinued nub- miniature CO. tubes 68F7 and 6507 and receiving tube 6BQ7. In- LOWELL MANUFACTURING St. Louis 17, Missouri creased price on germanium en-stal diodes 17460 to 5.75 West, Toronto, Canada net and 1N105 to 5.75 net. In Canada: Atlas Radio Corporation, Ltd., 560 King St.,

AUDIO ENGINEERING MARCH. 1953 67

www.americanradiohistory.com SELECTIONS !from page 24]

SAVE control may not be able to compensate Discussions of aural balance' have for the characteristics of both the record indicated that approximately equal fre- and the reproducing equipment. quency distortion, geometrically relative 33;% It has been established by several in- to the frequency mid -point, is more de- vestigators that record -surface noise is sirable than unequal frequency distor- fairly evenly distributed over the fre- tion, but that there is considerable lati- quency spectrum on the basis of energy tude in design for balanced response. content per cycle. Since each arithmetic The parameters of treble attenuation for frequency interval has a similar amount achieving careful balance would be de- of noise energy, the noise content will This is our termined by a study of bass deficiencies increase with each successively higher likely to be met with. The treble attenu- GROUP SUBSCRIPTION PLAN octave.5 It is therefore correct to think ation discussed in previous paragraphs You and your friends and co- workers of perceived surface noise as increasing is fairly symmetrical to most of these can now save up to $1.00 on each sub- with frequency, and compensation for low- frequency deficiencies. scription to AUDIO ENGINEERING. treble preemphasis in recording is very It will be seen The that the transition fre- more men in a Group, the more effective in reducing scratch, as the quency suggested each saves. If you send for treble attenuation 6 or more sub- system intends it to be. is scriptions for the U.S.A. and Canada, different from that for treble boost, they will cost each subscriber $2.00, There is however, an advantage in and conditions are likely to exist in being 1/3 less than the price of a regular able to introduce sharp cut-offs at which both are required simultaneously. 1 -year subscription. Present subscrip- given points of the frequency band, since Such simultaneous compensation, tions may how- be renewed or extended as records which have little or no fre- ever is inherently barred when part of a Group. a single quency content above the cut -off point control is used for both boost and cut. AUDIO ENGINEERING is still can then have their surface noise reduced without the The only publication devoted signal being severely Bass Boost entirely to Audio- penalized. Some types of distoration are Recording also most pronounced in the range above The conditions requiring bass boost Broadcasting equipment 5,000 cps, and sharp cut -off helps reduce are: Acoustics such effects with least change of 1. Decreased hearing sensitivity Home reproduction the sig- to systems nal. Sharp cut -off at high frequencies, bass frequencies at low sound intensities PA systems (Fletcher Psychoacoustice however, is incompatible with the other -Munson effect). duties of the treble tone control, 2. Recording characteristics whose and bass turnover frequency (Please print) should be accomplished by separate net- is higher than the one for which the repoducing equip- Name works. The general tone control must be ment is designed. Address limited in its scratch reducing role to a 3. Bass deficiencies in records. more gradual attenuation of the treble 4. Bass deficiencies in reproducing or band. studio equipment. Position Company Certain microphones, if incorrectly The well known family of equal loud- equalized at the studio, have a rising ness contours published Nam treble response by Fletcher and above one or two thou- Munson makes it Address sand cps. Attention evident that the appar- is occasionally called ent frequency to this characteristic when broadcast distribution of energy in given program material will vary greatly Position studio use of an incorrectly compensated Company microphone produces over -crisp and at different intensity levels. If the ampli- "hissy" fier has a correctly designed compensat- Name speech. The compensation required for this type of emphasis is coming network associated with its volume Address patible with that already planned for control this effect will be counteracted, records. but the volume control setting required Position Company Tonal balance of bass and treble for for a desired intensity level is not neces- the most satisfactory over -all result is sarily an accurate index of the intensity Name an inherently subjective problem. Like level of the original program, and fur- compensation Address for the Fletcher -Munson ther adjustment may be necessary. The effect, it involves a decrease of objective electrical level of an input signal does fidelity for the sake of an increase in not have a constant relationship, in dif- Position Company apparent realism. The fact that the prob- ferent program material, to the sound lem is one of perception rather than of level which it represents. Nm reality indicates that investigation re- The purpose of volume compensation Address quires a statistical technique" is not, of course, to straighten out the curve of frequency perception, (that's the way the music sounds in Position Company 5 B. B. Bauer, "Crystal pickup compen- the con- sation circuits," Electronics, 17, p. 128, cert hall) but to shape this curve at the reproduced kam Nov., 1945. intensity level so that the perceived frequency distribution is e It is suggested simi- Address that a useful approach lar to the perceived would be to compile judgment data in distribution at the which the jury compares various conditions original intensity. We may take 80 dbs Position Company of tonal balance, both symmetrical and as the average level of a 75 -piece or- asymmetrical to 800 chestra heard from Add $.50 cps, with the full a good seat, and 50 to each Foreign subscription range of sound, indicating which condition ordered seems more like the undistorted one. (Ask- ing the jury to indicate preference between ' Hugh S. Knowles, "Loudspeakers and RADIO MAGAZINES, INC. balanced and unbalanced conditions, with- room acoustics," The Radio Engineering P. O. Box 629, Mineola, N. Y. out an ever -present standard, involves the Handbook, Keith Henney, editor, p. 881, danger of measuring factors other than ap- 3rd edition, 1941. parent frequency distortion.) s Ibid.

68 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com db9 as the lowest level at which this between that for a high turnover fre- music is likely to be reproduced, with quency and for record and equipment any concern for quality, in the living deficiencies, and the compromise para- room. Superimposing the two appro- meters that appear most reasonable to 1,1loge priate curves on the same horizontal the writer include a transition frequency axis (Fig. 4), it will be seen that in one octave down from the spectrum mid- order to achieve the original perceived point, or 400 cps, and the standard maxi- frequency distribution in reproduction mum boost rate of 6 db per octave. HEADQUARTERS FOR at the 50 -db level, bass boost at slightly more than 6 db per octave, with a SOUND EQUIPMENT is transition frequency of 400 cps, re- Bass Attenuation quired. This is, of course, for the extreme case of a 30 -db difference between Bass attenuation may be required for INDUSTRIAL SOUND the original and the reproduced level. the following conditions: for any and all installa- At this 30 -db difference the bass boost 1. Recording characteristics with a required during orchestral peaks, when bass turnover frequency lower than that tions. Continuous music both levels may be increased by 20 db, of the reproducing equipment. or business message up 2. Accentuation and distortion of bass is much less ; during very soft passages to 8 hours. 4 the boost required will be more. We frequencies by reproducing equipment. j air must work on the basis of the average 3. A weak treble which creates tonal levels. imbalance. Illustrated: MAGNE- . The 50- and 80 -phon curves, and the The required compensation for equip- CORD Units PT6J, ` 60- and 70 -phon curves in between, are ment designed with a 500 -cps turnover, PT6AH, 814, with auto- practically identical in shape and slope and playing a record with a turnover matic switching equip- frequency of 250, 300 or 400 cps (all of from 500 cps up, meaning that a re- ment, custom built by which values have been used) may be duction of intensity level from 80 db Air -Tone Sound & Re- 50 db will produce no approximately achieved by a gentle at- to significant cording Co. change in the apparent frequency dis- tenuation of about 2 db per octave from tribution in the treble region. Even if it 750 cps down, or by a sharper downward were desired to compensate for the 2- slope from a lower transition frequency db maximum loss in treble, the ordinary of 500 cps. The second method is more R -C network could not produce the consistent with the other requirements necessary shape of response curve, of bass cut. which may be read from Fig. 5 as a Bass accentuation in reproducing *I-- uniformly elevated plateau over most of equipment is most often associated with lc' the treble spectrum. Correct volume acoustical resonance of an open speaker SOUND AND RECORDING CO. compensation should therefore involve enclosure at some frequency below 200 1527 CHESTNUT ST. no adjustment of treble frequencies. cps and with mechanical- acoustical reso- RI nance of the PHILA. 2, PA. -6 -8388 If the record reproducing equipment speaker system below 100 has cps. The effects of tone -arm resonance only a single turnover frequency a and turntable rumble usually compromise value of 500 occur be- to 600 cps is low 50 cps. As in the of low for every application... usually chosen. Some records have been case -frequency boost, we cannot furnish accu- made with higher turnover frequencies rate as compensation for equipment frail- high as 800 cps. Thus a moderate ties at the extreme low amount of boost to add to end, but we can that of the alleviate the condition in some fixed equalization will on occasion be measure. Aural balance of a weak treble ap- most complete - called for. Such equalization, however, is pears to demand a low transition fre- most diversified required by a relatively small number quency. Probable line in the worldl of records. treble droop occurs, as we have seen, at least two octaves Acoustically recorded discs, and some above 800 cps, and geometrically sym- electrically recorded ones, have a thin metrical bass losses would begin at bass because of weaknesses in recording about 200 cps. equipment and techniques. These ordi- A reference frequency and slope to narily require boost below two or three compromise between the various re- hundred cps, although the drop in bass quirements for which bass attenuation response is in general too sharp for will be needed are: transition frequency adequate compensation. From a professional 500 cps, maximum slope, 6 db per octave. boom stand to a Bass deficiencies in reproducing equip- flexible goose neck to o tiny . ment, fitting- whatever your need in like treble deficiencies, alto tend mike stands and accessories- to occur towards the extreme of the depend on it, ATLAS has it for Conclusion you. Desi3ned and eanufac- frequency scale. Most moderate quality turd for highest stability, loudspeakers (see Fig. 2), pickups, etc., Figure 5 is of tone -control quiet, ease of operation, dura. a graph bility. And backed sp 100% do not show a significant drop in bass frequency characteristics chosen on the by ATLAS -world 'statist in mike response until frequencies below 100 cps, basis of the above discussion. The stands, p+blic address loudspeakers and accessori., for 21 and then with sharply dropping curves. parameters vary from many of those in years. Here too compensation cannot be ade- common commercial use in that the ref- Compare them all at your distributor- You'II make your next quate. erence frequencies are shifted away mike stone an ATLAS Adjustment for the Fletcher- Munson from the spectrum mid -point, about one effect is probably the most frequent func- octave down for the bass, and two oc- tion of bass boost. The transition fre- taves up for treble boost. As a conse- quency required for this equalization lies quence the total amount of control is somewhat less than is often provided. Figure 6 is a tone control circuit with 9 "Frequency Range and Power Consid- erations in Music Reproduction," Jensen values assigned to approximate these Technical Monograph No. 3, Jensen Manu- curves. Some allowance has been made facturing Company. Note that a level of for the fact that the transition frequen- ATLAS SOUND CORP. 50 db is less than 10 db above the average cies are affected by the degree of boost 1448 -39th Street, Brooklyn 18, New York random noise level in a city apartment. or cut used by the operator. I- Coodo do, froPo Carp , lid . Tor

AUDIO ENGINEERING MARCH, 1953 69

www.americanradiohistory.com NOW Hear This NEW CHECKLIST CLASSIFIED Rates: loe per word per insertion for noncommercial [from page 14] advertisements; 25e per Word for commercial advertisements. Rates are net, and no discounts will be D430 only two or three and have them make allowed. Copy must be accompanied by remittance In 15" Speaker pronounced angles with each other Cult, and must reach the New York office by the and /or with the edge of the panel. first of the month preceding the date of issue. New pure iron, 18. If a studio organ is photographed THE AUDIO EXCHANGE, INC. buys lint "high intensity" with an organist, make sure each of his sells quality high -fidelity sound systems and hands is on a different manual (key- components. Guarantepped used and new equip- casting ment. Hillside board), the keys are depressed, some Ave., Jamaica 32, N. Y. Telephone OL 8-0445. structure stops are drawn, and the organist is looking at his music and not at the FOR SALE : Rek -O -Kat M-12, perfect condition with new LP feedscrew, Astatie WR -40 camera. With or without an organist, microphone, Chip-Chaser $75.00. TR -12 op- use a diagonal shot and make sure the tional, $75.00. Beekman t3 -6587 or Box CM -1. organ console and stop knobs or tabs Audio Engineering. are shined up for discreet highlights. MICROSCOPE. 40 MAGNIFICATION, Bausch & Lomb lenses, extension bracket and 19. On long shots, diamond- shaped post for mounting on any iliac recorder, $100. microphones like the RCA 44BX and Brush 3 -hour wire recorder, original cost $800, excellent condition $185. Reco-Art 74B and the Electro -Voice V series Company, 1305 Market St., Philadelphia 7, Pa. The heart of a fine loud speaker as its pow- show up best with one of their dead faces toward the camera and micro- ASSEMBLING A SYSTEM? Beat even erful magnetic structure. Jim Lansing the wholesale prices ! Custom installers write for phone tilted slightly. On close -ups, quantity prices on our 30 -watt Williamsons engineers have been able to produce and complete systems. Nicely Associates, in the new D -130 a more powerful these microphones and most others show Kenton, Ohio. voice up well in almost any position. magnetic beam across the coil 30% DISCOUNT ON ALL LP RECORDS!! than ever before possible. This unique 20. Turntables generally appear to Beet mail order service in the country. All best advantage when shot from an angle records factory -fresh and guaranteed. Spe- design extends the high frequency re- cializing in Hi -Fi records. Send for free sponse 25% and materially improves from above, with the pick -up in place catalog and literature. Southwest Record well toward the center of the disc to Sales, Dept. Æ -1, 4710 Caroline, Houston 4, the dampening factor. Hear this new Texas. Jim Lansing D -130 today ... at your emphasize the angle the arm makes with audio dealer's. the edge of the motorboard. FREE HI -FI CATALOG and Bargain 21. Price List. Chicago Electronics. 420 E. 87th Disc recorders also appear well St., Bpx 171, Chicago 19, III. Jim Lansing -first in fine sound! from an overhead angle. Swing the lathe over the centerpost with a disc on WANT used disc recorder with overhead JAMES B. LANSING SOUND, INC the platen, and place the camera so that lathe not driven from turntable center. Con- 2439 Fletcher Drove, Les Angeles 39, tact Box CM -3, Audio Engineering. California the lathe makes an appreciable angle with either edge of the cabinet. FOR SALE : Rek -O -Kut G-2 deluxe 16-in. turntable, $135 ; Gray model 108 -B viscous 22. Rack -mounted tape recorders damped arm, $40 ; Fairchild moving coil LP show-up best head -on, of course. Those cartridge, new point, $32.50 ; Altec 602 -A loudspeaker. $86 ; 10 -watt amplifier with Hi -Fi Values! in floor cabinets are best photographed Triad transformers, bass and treble controls. OLYMPIC Ultra -Lo Price! with the camera directly in preamp. $55. Robert Balluffi, 36 Wakefield front of and Ave., Port N. Y. somewhat above Washington. HI -FI WILLIAMSON TYPE the unit. Make sure both reels are on the machine and that FOR SALE : Altec Lansing M -11 microphone AMPLIFIER ' the tape is properly threaded systems (2) in perfect condition; in use one KIT month. Consists of 21 -B midget condenser y' : 23. Be careful of microphone, base, power supply. cable. $100 h shadows. Reduce per system. Box CM -2, Audio Engineering. or eliminate them by careful positioning and selection of spotlighting, backlight- SAVE! SAVE! SAVE! ON ALL THE NEWEST ing, sidelighting, etc. HIGH- FIDELITY EQUIPMENT 24. Will Phenomenal savings and guaranteed satisfac- enlargement and cropping tion assured through amazing new merchan- l'sing Stanror transformers. Easy -lo- assemble amplifier improve exposition or heighten impact? dise plan. Write for complete details and list. kit. Comes with schematic and instruction sheet based They often do, HI -FI GUILD, 45 -A Grove St., New York 14, on famous Williamson circuit. Frequency response I db. especially when the N. Y. from 20-50 kc at 8 watts. photo is intended SPECIAL to show considerable Intermodulat Ion distortion is in WANTED: Used Meissner 9 -1093 AM -FM only 3% at 8 watts outpsst PRICE detail, such as an -place picture of a PER KIT tuner and amplifier or Browning AM -FM Total harmonic distortion at terminal block. tuner. two selectivities. John Callan, 3819 1000 cycles is non- existant $44.95 Military Road, N. W.. Washington 15. D. C. below 10 watt power level. 25. Have your pictures retouched if they are for publication. Surface blem- KIT OF CBS HYTRON TUBES PRECISION 1% LOW -NOISE RESIST- ishes, forgotten shipping ORS. WILLIAMSON KIT: 1-47K 1w, 2 -20K FOR ABOVE AMPLIFIER tags and other embarrassing details can be removed in 1w, 2 -.47 meg ;w, 2 -50K 2w, 2 -.1 meg íw- Consists of: 2 -GLB07 2- 65N7GT 1.5046 $5.00. Single resistors : kw 43e, 1W 68e. 2W varying 15#. Edwin Bohr, SPECIAL ONLY degrees by an expert re- toucher. 88e. Shipping charge Day- $7.95 Don't try it yourself. ton Pike, Chattanooga 5, Tenn. IRISH PLASTIC RECORDING TAPE 26. Beware of even slightly- overde- BRAND NEW! NOT SURPLUS. This veloped prints if the photos are for pub- First Grade recording tape is t/ In. lication. Detail necessarily suffers when wide. Frequency response: 50 to 8,000 rs. Plastic reel Included with each. a photograph is reproduced on the 600 FT. $1.35 1,200 FT. $2.10 printed page and dark areas often appear still darker. Make sure of good detail BEST BUY OF THE MONTH! in both light and dark areas. AM -FM TUNER 27. Try to get the proper exposure on 10 W. III -Fl PI'Sll -PULL AMPLIFIER Freq. response

20-20.000 riw. at less than 'h of ! ' . distortion. the negative so that the pointers and New 532.95 scales on the meter dials show up COMING OUR WAY' Be sure and visit our new HI -FI, plainly acoustically designed sound studio: and clearly. All orders F.O.B. Los Angeles. Minimum order 28. Glossy prints on contrasty paper, 55.00. 25°c deposit required with order. and of a size not smaller than 4 x 5, are OLYMPIC ELECTRONICS SUPPLY required. Many editors will not accept Distributors ,1440 W. Olympic Blvd., Los Angeles 15, Calif. prints smaller than 8 x 10. 29. Furnish brief but clear captions

70 AUDIO ENGINEERING MARCH, 1953

www.americanradiohistory.com fastened to the picture, preferably by pasting on the back. Editors, alas, are PROFESSIONAL not mind readers. And don't ever use 21c1444 .. . FREE! paper clips to hold together a number DIRECTORY of photos. wowE 30. Last, and of greatest importance, is to make sure that your pictures are sharply focused -"wire sharp" is the Custom -Built Equipment term often used by photographers. Re- member that the best photos lose something in reproduction, and sharpness in U. S. Recording Co. the original is yen, important. 1121 Vermont Ave., W.shisgtos 5, D. LIncoln 5-2705 90,rhabil peaple . David Sarser and his sister Sebe, still appearing under the guidance of impressarlo Maximilian Weil, president of Audak Com- pany, repeated their New York Audio Fair success at the \Vest Coast Fair ... Debbie "EVERYTHING IN HIGH FIDELITY" Isiloa, director of public relations for Co- From Primary Components lumbia Records, Inc., is assembling a to Completed Custom Audio Equipment brand new high -fidelity music system -the TERMINAL'S better to hear the line records she pub- New, Illustrated, 130 -page licizes, no doubt . Another distaffer, Margaret Delano of Harper & Brothers, KIE F publishers, is plenty hep on audio as a result of handling the editing assignment on Sound Corp. Edward Tatnall Canby's new book- sched- AUDIO uled for March 18 publication . . . Les West Olympic Blvd. Los Angeles 15, Calif. Paul, Capitol Records star, is on verge of 820 completing one of the country's most CATALOG Richmond 7 -0271 ZEnith 0271 lavish recording studies, built as an addition to his New Jersey home -among its Your complete guide tc tI-e amenities are such audio hors d'oeuvres as Finest in Audio Equipment! six Ampexes, one disc recorder, Telefunken microphones, etc.... Bob Silverman, pro- Write o come in for you In Southern California it's gram director, station WABF, busily pre- paring a special audio issue of the sta- FREE Complimentary Cop -! HOLLYWOOD ELECTRONICS tion's monthly program -listing magazine Visit our Audio Dept. Gil Demsky, Anton Schmitt, and Thurs. eves. till 9 P. M. (in The Audio Mile) Jimmy Carroll, custodians of Harvey Open Radio Company sound department, are Ample Poling Spore after 6 P. R. Distributors of Hi Fidelity initiating campaign for improved broad- Components Exclusively cast quality of New York Philharmonic Webster 3 -8208 and NBC Symphony concerts -all three Terminal Radio Corp. have been recording the concerts off the 7460 Melrose Ave. Hollywood 46, Calif. air for years, and are unanimous in the I85 Cortlandt St., New York 7 opinion that audio quality has deteriorated noticeably in recent months . Michael von Mandel, American legal and sales representative for Germany's Telefunken Company, off for three -week visit with ELECTRONIC company officials in Europe George Silber, president of Rek -O -Kut Company, ENGINEER called home from California the night be- Audio high -fidelity development and ap- fore opening of Audio Fair -Los Angeles plication engineer. Thorough knowledge of due to fire which destroyed portion of ctnnh,C0 EASY -HANDLING company plant ... Tom Dempsey Is new ad current trends in audio field. manager for Reeves Soundcraft Corp.- WRITE STATE SALARY DESIRED -formerly with J. M. Mathes ad agency MAGNETIC TAPE REELS Box AE 1784, 221 W. 41st St., N. Y. 36 P: Sumner Hall, president of Audio Equipment Sales, has perfected a new Precision manufactured in ordance telephone plug to end all plugs-contains with the exacting standards aset by th many unique and original features . Entire audio fraternity well entertained and enlightened at February meeting of ) AES in New York -featuring many of Announcing the opening of the the most prominent personalities in the BROOKLYN HIGH FIDELITY SOUND CENTER audio field in a round -table discussion -on the platform Ns CI, Wilfred B. Whalley, 2128 Caton Ave., Bklyn 26, N. Y. moderator, C. J. LeBel, Frank H. McIntosh, (Cor. Flatbush Ave.) Jerry B. Minter, H. A. Pearson, Herman Tel: BUckminster 2 5300 H. Scott, :I n,l Llewellyn Bates Reim Elton Nachman, formerly with Audio - High Fidelity Components and Complete Systems Video Products Corp. getting acclimated Write for Brochure to new position with Sun Radio & Elec- tronics Corp.

handle bas oohed WANTED: DIRECTOR OF ENGINEERING dy.s ore sm Easy le ° and shore An outstanding opportunity for an electronics engineer of executive caliber to head quickly away. up the development program for a nationally known manufacturer in the electronics field. cots assemble Epm C fm Pan A smaller firm with two well- equipped plants and excellent laboratory facilities, particu- 2. stay Ito'. linens larly in the audio and electro- acoustic fields, 7000 of the company's business is civilian. Alum. °u1° 3. 'elstonic' Starting salary $12,000 with opportunity for increased earnings through bonus and no's tape io. os to O se few finish ° advancement. Stock participation open. Appointee will be a member of small top manage- 4. Hubs, ,le -en ment group. S. ne'- 10f editing QUALIFICATIONS: Must be a graduate engineer or physicist, preferably in com-

munications field. Age: 30 -50. At least 8 years of engineering experience with some TAPE REELS. STORAGE CANS. AND SNIPPING supervisory activity. American citizenship and clearance for secret. and creative CASES fOR EVERY PROFESSIONAL 1(0511E- Originality MENT ALWAYS IN STOOL thinking essential plus ability to plan, organize, and coordinate the efforts of various D ",Its for deurip:re lir"umre and pit. fit project groups. COMPCO CORPORATUON PERSONAL may IRE in .I.:::,, .,, moor of fire product, la. for Ardio CONFIDENTIAL INTERVIEW be arranged during meeting Visual industry. March in N.Y.C. Address reply stating personal qualifications, including: education, em- 2251 W. St. Paul Ave. Chicago 47, Illinois ployment and earnings record, patents and inventions, publications, interests, family status. Box DM -1, AUDIO ENGINEERING, P. 0. Box 629, Mineola, N. Y. All replies treated in strict confidence. Our own staff knows of this advertisement.

AUDIO ENGINEERING MARCH, 1953 71

www.americanradiohistory.com YOU CAN NOW GET THE FAMOUS ADVERTISING HARTLEY 215 SPEAKER SO EASILY INDEX

AND IN THE UNIQUE "BOFFLE ". Air Tone Sound & Recording Co 69 Allied Radio Corp. 43 Altec Lansing Corp. 53 idle. Our factories Since our last advertisement we have been far from Amperite Co., Inc. 64 in London and New York have been working hard to provide you with a Ampex Electric Corp. 11 Hartley service as satisfactory as Hartley reproduction. From now on we Arnold Engineering Co. 15 can deliver from New York stock, having done all the tedious work in im- Asco Sound Corp. 2 porting, clearing customs, and acceptance testing. The 215 is HERE, ready Atlas Sound Corp. 69 to be shipped at once to any part of the country, without delay, without Audak Co. 47 ocean hazards. Audio Devices Inc. Cover 2 Concurrently, we have the unique non -resonant Boffle also available Audio Instrument Co., Inc. 58 Bell Telephone Laboratories 18 r in a variety of finishes and styles, made from the finest American materials Brooklyn Hi- Fidelity Sound Center 71 and workmanship. For extreme economy we have preserved the knock -down Brush Development Co, 4 kit of parts, easily assembled in an hour or two; yet although of much finer Camera Equipment Co. 57 quality than those we used to send from England, the price is actually less. Cannon Electric Co. 10 Boffles are made from half -inch stock, the front panel being three - Chicago Transformer Co. 51 quarter inch tough board; all joints are keyed and glued; polished or un- Cinema Engineering Co. 7 polished; veneered in oak, mahogany or walnut; also in unfinished pine, if Classified Ads 70 you need a truly inexpensive housing for insertion in an existing cabinet. Compco Corp. 71 And the finest possible results, regardless of expense, we intro- -for Concertone Recorders 61 215's wired in simple series, will duce the double Boffle, which, with two Diacoustic Laboratory 59 by any give you for $200 a performance not to be equalled speaker en- General Electric Co. 56 semble offered elsewhere at prices up to more than $1000. Demonstra- General Radio Co. 13 tion will prove this claim. The double Boffle can be used horizontally or Gray Research & Dev. Co., Inc. 5 vertically and measures 30" x 18" x 18 ". The single Boffle remains at 18" Hartley, H. A. Co., Ltd. 72 x 18" x 18 ". Harvey Radio Co., Inc. 45 Heath Co. 59 Hudson Radio & Television Corp. 66

Hughes Research & Dev. Labs 1 Prices Institute of Radio Engineers 65 Jensen Mfg. Co. 41 THE HARTLEY 215 SPEAKER $57.50 Kierulff Sound Corp. 71 Lansing Sound, James B., Inc. 70 THE TRUE -BASS BOFFLE Leonard Radio Inc. 55 Lowell Mfg. Co. 67 FINISH SINGLE DOUBLE Maurer, J. A. Inc. 35 Minnesota Mining & Mfg. Co. . 36, 37 Veneered in mahogany or walnut, completely finished $75.00 $85.00 oak, Olympic Electronics Supply Co. .. 70 do do do do unpolished $50.00 $55.00 Orradio Industries Inc. Cover 3 do do do do kit of parts $40.00 $45.00 Ltd. 67 Unfinished pine (can be stained and polished or painted) $40.00 $45.00 Partridge Transformers, .... do do kit of parts $30.00 $35.00 Peerless Electrical Products Div. .. 14 Pickering & Co., Inc. 17 Pilot Radio Corp. 48, 49 Inc. 64 HARTLEY TONE- CONTROL PREAMPLIFIER $35.00 Precision Electronics, Precision Film Laboratories 12 HARTLEY 20 AMPLIFIER WATT $135.00 Presto Recording Corp. 39 Complete with tubes. Prestoseal Mfg. Corp. 66 Professional Directory 71 If you have not already asked to be put on our mailing list, send a postcard Radio's Master 52 to London today, so that you can be kept fully informed on all our new ideas. Reeves Soundcraft Corp. 9 CANADIAN CUSTOMERS SEND TO LONDON FOR OUR Rek -O -Kut Co. 3 SPECIAL PRICE LIST. Rockbar Corp. 56 Shure Bros. Inc. 6 Sonocraft Corp. 50 Stromberg Carlson Sound Div. 63 Sun Radio & Electronics Co., Inc. 61 H. A. HARTLEY CO. INC. Terminal Radio Corp. 71 Triad Transformer Mfg. Co. 60 521 East 162nd St., New York 56, N. Y. LU 5 -4239 Tung -Sol Electric Co. 8 United Transformer Co. .... Cover 4 H. A. HARTLEY CO. LTD. U. S. Recording Co. 71 Wholesale Radio Parts Co., Inc. 62 152 Hammersmith Road, London W.6, Eng.

72 AUDIO ENGINEERING MARCH, 1953

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SOUND -PLATE a ç reater surfyce slip Yes, SOUND -PLATE costs a little more ... but, in the long run, it will prove to be not only the most satisfactory. but the most economical magnetic An,tFer Reason WHY SOUND -PLATE r_cordin5.! tape you can use. is Best For Professional Use! Try SOUND -PLATE at our expense! Buy a reel of SOUND -PLATE at your Thee ue differences in magnetic oxide: ORRodio favorite Radio Parts Distributor. If you are not completely satisfied, return molecular lobicoted oxides are more stab e in coat- i- to your distributor who has been authorized to refund your money. ing conditions and turn out snore uniform dsF ers ons, thus ass.rrng you of the rires, recordings possible. 1200 Ft. SOUND-PLATE on Plastic 2400 Ft. SOUND -PLATE on Meta. SOUND-PLATE is made in the ORPodio traíi'ion . Reel $15.50 List Reel $33.85

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www.americanradiohistory.com for Stock Hermetically Sealed Components

t VO s a . pp er o ns MOT' comp nents for military applications, to customer specifications. Listed below are a number of types, to latest military specifications, which are now catalogued as UTC stock items.

._ MINIATURE AUDIO UNITS...RCOF CASE

Type MIL Pri. Imp. Sec. Imp. DC in Response Max. level Litt No. Application Type Ohms Ohms Pri., MA ± 2db. (Cyc.) dbm hier. H-1 Mike, pickup, line tc grid TF1A10YY 50,200 CT, 500 CT- 50,000 0 50- 10,000 } 5 $16.50 H-2 Mike to grid TFIAlIYY 82 135,000 50 250 -8,000 +21 16.00 H-3 Single plate to single grid TF1A15YY 15,000 60,000 0 50- 10,000 + 6 13.50 H-4 Single plate to single grid, TF1A15YY 15,000 60,000 4 200 -10,000 +14 13.50 DC In Pri. H -5 P.P. TF1A15YY Single plate to F rids 15,000 95,000 CT 0 50. 10,000 + 5 15.50 H -6 Single P.P. TF1A15YY RCOF CASE plate to grids, 15,000 95,000 split 4 200 -10,000 +11 16.30 DC in Pri. Length 1 25/64 H -7 Single or P.P. plates t3 line TF1A13YY 20,000 CT 150/600 4 200 -10,000 +21 16.50 Width 61/64 H -8 Mixing and matching TF1A16YY 150/600 600 CT 0 50- 10,000 8 15.50 Height 113/32 + H -9 82/41:1 Input to grid TFIAIOYY 150/600 1 meg. 0 200 -3,000 (4db.) +10 16.50 Mounting 11/8 H -10 10:1 single plate to Bing le TF1A15YY 10,000 1 meg. 0 200 -3,000 (4db.) +10 15.00 Screws 4-40 FIL. grid Cutout 7/8 Dia. H -11 Reactor TFIA2OYY 300 Henries -0 DC, 50 Henries -3 Ma. DC, 6,000 Ohms. 12.00 Unit Weight 1.5 oz.

COMPACT AUDIO UNITS...RC -50 CASE

Type MIL Pri. Imp. Sec. Imp. DC in Response Max. level List No. Application Type Ohms Ohms Pri., MA -!- 2db. (Cyr..) Om Prl:e

H -20 Single plate to 2 grid:, can TFIA15YY 15,000 split 80,000 split 0 30- 20,000 +12 $20.70 also be used for P.P. plates H21 Single plate to P.P. grids, TF1A15YY 15,000 80,000 split 8 100-20,000 +23 23.70 DC in Pri. RC -50 CASE H -22 Single plate to multip e line TF1A13YY 15,000 50/200, 8 50. 20,000 +23 2130 Length 15/8 125/500' H 2030 Width 1 5/8 -23 P.P. plates to multipla line TF1A13YY 30,000 split 50/200, 8 30- 20,000 +19 Height 25/16 125/500' BAL. H -24 Reactor TF1A20YY 450 Hys.-0 DC, 250 Hys.-5 Ma. DC, 6000 ohms . . . 15.30 Mounting 15/16 65 Hys.10 Ma. DC, 1500 ohms. Screws #6 -32 Cutout 1 1/2 Dia. Unit Weight 8 oz.

SUBMINIATURE AUDIO UNITS...SM CASE

Type MIL Pri. Imp. Sec. Imp. DC in Resporse Max. level List Ho. Application Type Ohms Ohms Pri., MA 2db. (Cyr..) dbm Prise H -30 Input to grid TF1AlOYY 50 62,500 0 150- 10,000 +13 313.00 H -31 Single plate to single grid, TFIA15YY 10,000 90,000 0 300 -10,000 +13 13.00 3:1 H -32 Single plate to line TF1A13YY 10,000 200 3 300 -10,000 +13 13.00 SM CASE H -33 Single plate to low TF1A13YY 30,000 50 1 300-10,000 +15 13.00 Length 11/16 impedance Width 1/2 H -34 Single plate to low TF1A13YY 100,000 60 .5 300 -10,000 + 6 13.00 Height 29/32 Impedance Screw 4-40 FIL. H -35 Reactor TFIA2OYY 100 Henries -0 DC, 50 Henries -I Ma. DC, 4,400 ohms. 11.00 Unit Weight 8 oz.

The impedance ratings are 200 ohm termination can be used for 150 ohms or 250 ohms, 500 ohm termination can be used for 600 ohms. listed in standard manner. 200 ohm termination can be Obviously, a transformer with used for 150 ohms or 250 ohms, 125/500 ohm termination can be used for 150'600 ohms. a 15,000 ohm primary imped- can be used with higher source Impedances, with corresponding reduction in frequency range. With 200 ohm source, ance con operate from a tube secondary impedance becomes 250,000 ohms ... loaded response is -4 db. at 300 cycles. representing a source imped- 'can be used for 500 ohm load ... 25.000 ohm primary impedance ... 1.5 Ma. DC. ance of 7700 ohms, etc. In addition, transformers can b used for applications differ- ing conslderobly from those shown, keeping In mind that impedance ratio is constant. Lower source Impedance will / improve response and level ratings ... higher source im pdance will reduce frequency /041i04 ,ah range and level rating.

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