Audio Engineering Magazine March 1953

I

here are the 30 BEST SELLING RECORDS OF 1952*

• • . and over 4370 used. audiotapet for the origina..l $.(i}itJ;nd!

Like Audiodiscs and Audiotape, this, 1j€l,:o.l'd' speaks. Made from Audiodisc for itself. Record, Artist & Label Master Of the thirty top hit records of the, year, all but BLUE TANGO (Leroy Anderoon-Decca) ...... •. WHEEL OF FORTUNE (Kay St"arr-Capitol) ...... one were made from Audiodisc maste.~s ! And that. CRY (Johnnie Ray-Okeh) ...... one - a London Record - was made ~broad. 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-Col1Lmbia) ...... • for over 43 per cent of these records W€lje fiorst made­ WISH YOU WERE HERE (Eddie FiBher- Hugo ll;interhalter- Victor) ...... on Audiotape, then transferred to the. master discs., HERE IN MY HEART (AI Martino - BBS) ...... •.•. This marks a growing trend towar ~ t4e use of D~LICADD (Percy Faith-Columbia) ...... • KISS OF FIRE (Georgia Gibbs-Merc1Lry) ...... " . . ..•.. Audiotape for the original sound in 1iQ.e: wanufac-. ANY TIME (Eddie F isher-Hugo Winterhaiter-V ictor). ture of fine phonograph records. TELL ME WHY (Four Aces-Decca) ...... BLACKSMITH BLUES (Ella Mae Morse-Capitol) ...... Yes - Audiodiscs and Audiotape- %1ie- truly a JAMBALAYA (Jo Stafford-Columbia) ...... BOTCH·A·ME (RoBemary Clooney-Columbia) ...... •. record-making combination-in a fiel;dl w4ftre there; GUY IS A GUY (Doris Day-Columbia) ...... can be no compromise with Quality.!! LITTLE WHITE CLOUD THAT CRIED (Johnnie Ray- Okeh) : HIGH NOON (Fran kie Laine-Columbia} ...... I'M YOURS (Eddie Fisher-Hugo Winterhaiter-Victor) GLOW WORM (Mills Brothers-Decca) ...... IT'S IN THE BOOK (Johnny Standley- Capitol) . .• .. ..•. SLOW POKE (Pee Wee King-Victor) ...... •...... WALKIN' MY BABY BACK HOME (Johnnie R ay-Columbia) MEET MR. CALLAGHAN (Les Paul-Cap'itol) ...... , .... . I'M YOURS (Don Cornell-Coral) ...... I'LL WALK ALONE (Don Cornell-Coral) ...... • TELL ME WHY (Eddie FiBher-Hugo Winterhaiter-Victor) TRYING (Hilltopper8- Dot) ...... PLEASE, MR. SUN (Johnnie Ray-Columbia) .... : ...... AUDIO DEVICES, INC. * According to Retail Sales. as listed in THE BILLBOARD. 444 MADISON AVE., NEW YORK- 22, ..,.. '(- Export Dept.: 13 East 40th St ., New York 1 , ~.':( r, .Y;~

, INClUDING' >~ PHYSICISTS AND ENGINEERS c. G. McProud, Editor and Publisher Harrie K. Richardson, Associale Editor Edgar M ~ Villchur, Contributing Ed"itor ATTENDING THE Eve Drolet; Production Manager Henry A. Schober, Business Manager· " Edgar E. Newman, Circulation Promotion' S. L. Cahn, Advertising Director ,~> Elizabeth Beebee, Circulation ~anager H. N. Reizes, ~dverNsi n gL.M=a!.'-n!"acfU.e !...r _~~=-JI , IoRoEo CONVENTION Editorial Advisory Board Representatives H. Thorpe Covington. Special Representative NEW YORK CITY Howard A. Chinn 677 N. Michigan Ave .• Chicago 11. III. Sanford R. Cowan, Mid-West Representative MARCH 23 - 26 ... lohn D. Calvin 67 W. 44th St., New York 18, N. Y. C. I. LeBel West Coast I. p. Maxfield Inquiries are lames C. Galloway J. W. Harbison ,~ George M. Nixon 816 W. 5th St., Los Angeles 17, Calif. invited regarding CONTENTS MARCH, 1953 Vol. 37, No. 3 openmgs Audio Patents- R'iehard H. Dort ...... , . 2 on our Staff Letters ...... , ...... 8 Employment Register ...... , ...... 10 ~ RADAR LABORATORIES New Literature...... 12 ~ GUIDED MISSILE LABORATORIES Audio Photographer's Check li st-E~,§ene F. Coriell ...... , 14 ~ ADVANCED ELECTRONIC LABORATORIES Effect of .Load Impedance on Magnetic Pickup Response-Norman P iekering 19 ~ ELECTRON TUBE LABORATORIES

A Power Tube Figure of Merit- Warren G. Bendel' ...... 21 ~ FIELD ENGINEERING DEPARTMENT The Selection of Tone-Control Parameters- Edga,,. M. Vale/llrl' ...... 22 Audio in the Year 1693-Allen H. FIns...... 25 " For the conllenience of Auxiliary or Emergency Broadcast Control Rqom-Ha :rald Reed ...... 26 > :~ those attending the I. R. E. The Columbia "360"- Peter C. Goldma4'k ... , ...... 28 , meetirrgs arrd Radio Engineering Theater Sound in A Small Package-Part 2-Tho1llas R. H ·nghes .. ,...... 30 Show, members of the Handbook of Sound Reproduction-Chapter lO-Edgar M. Villehu.-r ...... 32 Laboratory Staff //Iill be al/ailable 1953 Radio Engineering Show ...... 38 for i1'lterll iews at the First Inventor Under the 1952 Patent Law-Albert Woodnrff tray...... 40 Convention hotel. For appoilltlllent telephone Hughes New York Audio Fair-Los Angeles Rated Huge Success...... 42. office, LAckawanna 4-935 0 . Equipment Report-Pilotllne'r and Pilotone Amplifier .... , .. ,...... 44 Record Revue-Ed~vQ.1·d Taf1wll 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 RESEARCH AND Magnestripe process is being demonstrated by Georgia Landeau, DEVELOPMENT LABORATORIES NBC-TV featured actress. At the left is shown the RCA Moclel Scientific and 400 projector which reproduces both optical and magnetic Engineering Staff s.ound tracks, and which incorporates a recording CULVER CITY, LOS ANGELES amplifier for use with the Magnestripe process, COUNTY, CALIFORNIA

RADIO MAGAZINES, INC., P. O. BOX 629, MINEOLA, N. Y. Assurance is required that relocation of the applicant will not cause disruption AUDIO ENGINEERING (Utle registered U. S, Pot. Olt.l Is published monthly at 10 McGo'ern Avenue, Lancaster, Pa. by of an urgent military project. Radio Magazines, Inc., Henry A. Schober, President; C. G. McProud, Secretory. Encuti,e and Editorial Omces : 204 Front St., !Uneola, N. Y. Subscription rates-United States, U. S. PossessIons and Canada, $3.00 for 1 year, $5.00 tor 2 years; elsewhere $4.00 per year. Single caples 3·5c. Printed In U. S. A. All rights reserved. Entire contents ccpyrlght 1953 by Radio Magames, Inc. Entered as Seeond Class Matter Febmary 9, 1950. at the Post Office, Lan· caster, Pa. under the Act at March 3, 1879.

AUDIO ENGINEERING • MARCH, 1953 RICHARD H. DORP

T SEEMS that it is time once again to some really good thinking and problem repeat a definition given a long time ago solving. This column is a review rather I of the purpose of these monthly patent than a normal article, selecting as many articles. The thought arises because among interesting (to the writer, anywwriters, and they often give additional W hile 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 vVhenever 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. M'iiian- . . . and found con­ others. T hey don't purport to give ab­ sistently effective for fringe-area re­ solutely reliable information right from the Distortion Measurement 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 re~epti o n even in remote positively work. W hat 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 (AFe) 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 .·SiUeiii.! .. . because of its because there is an idea that could be de­ supenor per%rmance, 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 almost any enclosure, its new type precision equipment, and is shown in block sarily better-way of doing a common form in Fig. 1. tuning indicator (simpler to use) and thing, because, although the object of the many other exclusive features . . . The principle is to generate a wave of 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* * bl ack-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 fi les. 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 simplilied installation. patents issued monthly (to which most ancing circuit contains fhe difference be­ people don't have access and the time to SONOCRAFT FM TUNER $89.95 tween the original and distorted forms, 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 luner. *

Come in and pick up or write for your free copy of "Sound Advice" wrillen for Music Lovers, by Irving Greene. 124 pages of viral information in high fidelity.

.-- BALANCING BRANCH-:-

Fig. 1.

2 AUDIO ENGINEERING • MARCH, 1953 (

REK- -KUT

Record Reproduction begins with the rotating motion of the record! This motion expresses passage of time. And each rotation is an in- terval or segment of that time. This important function is en­ trusted to the turntable.

The faithfulness with which 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 de­ viation will result in a variation in time or tempo, a'nd in undulating pitch.

There is no compromise with turntable qual­ ity 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 sim­ ply a lover of good sound, only a fine turn­ table can justify the fine equipment of a modern high fidelity system. • • • • • • • • • • • •

Among the seven REK-O-KUT Turntables available are: Model LP743 -Induction Motor Three Speeds, 33 1/3, 45 ~ nd 78...... $ 54.95 . Model T-12H - Hysteresis Motor Two Speeds, 331f3 and 78 ...... 119.95 Model T-43H - Hysteresis .Motor Sold by Leadin~ Distributors Two Speeds, 33 1f3 and 45...... 119_95 Write for Descriptive Literature

RE K -0 -KUTe o. 38-03B QUEENS BOULEVARD· LONG ISLAND CITY I, NEW YORK Export Division : 458 Broadway , New York 13, U. S. A. Cable'S: Morhanex In Canada : Atlas Rad io Corp ., Ltd., 560 King Street W., Toronto 2B

AUDIO ENGINEERING • MARCH , 1953 3 B. FA OMSYST[M UNOER TE ST

1FROM AT TEN UAT OR A

1.-: Fig. 2. test branch is within the nominal capabili­ ties of the tested system. T hen the switch in the test branch is opened and atte,I1Ull.tor B is adj usted so that the oscilloscope trace has a peak vertical defl ection of 10 divi­ sions. Next the switch is closed and at­ tenuator C adj usted so that the two branch outputs are balanced by placing as much as possible of the center of the resulta[.\t wave on the zero horizontal axis on the osciJ.io­ scope screen. T he peak defl ection of the resultant wave then shows the amount of diffe rence 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 attenua­ tor D may be reduced by 20 db, which gives a factor of 10, making each division equal to 1 per cent dist0rtion. . 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 wave­ form, 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. TI, is tops for tape recording a phase-inverter stage which allows selec­ 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 ff0m the tested system. The input recording components can improve your tape recorders! potentiometer is equivalent to attenuator C in Fig. 1. The BK-I090 record-reproduce head has the standard track The output of the phase inverter is ap­ width designed for dual track recording on '.4 inch tape. It pro­ pli ed to the cathode of the b a la~cing (really vides unu:mally high resolution and uniformity over an extended simply a mixing ) stage, wIllIe the test frequency range. Cast resin construction assures dimensional branch output coming through a potent i­ 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 veTtical lapped gap, Mu-metal housing, and single-hole mounting provide amplifie r gain control acting as attenuator important design advantages. D. The BK-ll10 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 efficient erasing at low power consumption-less than Y, voltampere. circuits extant than any other device in the audio world. A lmost 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 Brush Electronics Company, Department 22·.),3405 Perkins A venue, dropoffs and di stortion. Here is a circuit Cleveland 14, Ohio~ the inventor claims will remain in perfect balance between 20 and 150,000 cps. Illus­ trated in Fig. 3, it was invented by Louis R. BRUSH ELECTRONICS COMPANY Bourget of Sacramento, Calif., and is the subj ect of patent N o. 2,618,71l. IN [ orlluTly INDUSTRIAL AND RESEARCH INSTRUMENTS The Brush Develolmumt Co. The ci rcuit uses three tr iodes ( two of PIEZDELECTRIC MATERIALS ACOUSTIC DEVICES -- Brush EleciTouics Co mpau'] which may be, as shown, the halves of a is an operating unit of dual-triode) . The first is operated as a MAGNETIC RECORDING EQUIPMENT ,- Ihdi-;i.t:it4J..---- ULTRASONIC EQUIPMENT --- Clevite Co rporatio1l . cathode foll ower, with R, the volume con- 4 AU.DIO ENGINEERING • MARCH, 1953 Here is the first basic advance · in tone arm design in many decades!

The GRAY"Viscous-Damped"

', : ~'" 108~B Tone Arm

Gives you perfect contact and tracking on all, records at , lowest stylus pressure - virtually eliminates tone arm reso­ nances - cannot damage record if accidentally dropped.

The entirely new suspension principle of The l08-B satisfies every requirement of the Gray l08-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 331;3- 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 tracking, virtually eliminates "viscous-damped" arm soon - solve all your tone arm resonances, and prevents any pos'­ transcription problems with this revolutionary, sihility of record damage if the arm is dropped. versatile arm!

·r------

I Gray Research & Development Co ., Inc. I Hilliard Street, Manchester, Conn. I Please send me your Bulletin RF·3 on the new Gray "Viscoy s·Damped" l08·B Tone Arm.

NAME

AND DEVElOPMENT CO., INC., HILLIARD STREET, MANCHESTER , CONN . ADDRESS Division of The GRA Y MANUFACTURING COMPANY- Originators of th e Gray Telephone Pay Stnti on and th e Gray Audograph and PhonAlldogrnJlh CITY STATE AUDIO ENGINEERING • MARCH, 1953 5 \ J

" INI fWle like it 4fo"\.e'fops" ~ they ... says RAY ANTHONY "The Young Man With a Horn"

• • • about the famous new Fig. 3 . trol and R. the cathode resistor. The secr~t 1 of the ci rcuit's success is said to be that the e slender gradient 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 tha.t 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 in­ put capacitance effects. Its output is, of course, out of phase with the circuit input. The output capacitances of both V, and V, H300 ~ ' should be the same, causing no unbalance such as would be obtained from the "long­ Broadcast tailed" or "split-load" circuits. Miller ef- liST PRIC.E $125.00

H315" General Purpose LIST PRICE $7 5.00

Fig. 4 . • fect is probably less in V. than in V, be­ cause there is some cathode degeneration in V •. For high-fidelity, true-tone reproduction of The latter probabil ity 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-and bands everywhere. in both tubes. This reduces the amplification of V" which is compensated by tapping the input for V. down on R. and adding the SOO -ohm resistor for bias compensation. The circuit of Fig. 4, by the way, is suitable for d.c. amplification because of the elimination of the V, cathode bypass capacitor and the output blocking capacitors. This may inter­ est instrumentation workers and direct­ coupling fiends in the audio field. In either circuit, R, should be adjusted for equal plate currents through V. and V,. In Fig. 4, the tap on R , may also be touched up a little if necessary for equal audio outputs. R, need not be adj ustable, 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. Video Beckons

MAN UFACTU RERS of I should like to close this chapter with a SHURE BROTHERS, Inc . suggestion which may provoke some audio * and A COUSTIC DEVICES engineers and enthusiasts (the terms are 22S West Huron Street, Chicago 10, Illinois • Cable Address: SHU REMICRO ( C ontin1{ed 011 /Jag e 56)

6 AUDio ENGINEERING • MARCH, 1953 The I.nside .Story

. The NEW CE Series .

ACCURATE WIRE WOUND RESISTORS

HERMETICALLY SEALED IN CAST EPOXY. 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 ho­ mogenous mass that means so much to stability and provides the ample moisture vapor barrier of this new resistor. Bobbin and encapsulation become one homogenolJs mass, surround­ ing 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.

IN NEW YORK: Audio & Video Products Corporation 730 fifth Ave. • Plaza 7 ·3091

EXPORT AGENTS: Frazor & Honsen, limited 301 Clay Street San Francisco, California, U.S.A.

AUDIO ENGINEERING • MARCH, 1953 7 here's LETTER'S Help W anted! SIR: absolute reliability A number of months ago I took up the subj ect 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 "H earing T ests and H earing Instruments," and Harvey. F letcher's "Speech and H earing." As yet we have not established where in the auditory system the difference between the two exists. We would appreciate any comments on this subj ect which audio your readers would cal'e to put forward. J OHN F. M c D ERMOTT, Flat 36, 2 Anderson St., amplification Kingsford, N .S.W., Australia.

Stereo Photos SIR: It is now a year since you fir st used stereo photos in the maga­ zine, and I have been waiting for fu rther use. I feel that they are a very good way of presenting devices that have interesting spatial features. I hope that you are continuing to solicit their use in future articles where they would be appreciated. ROBERT P . S T. J OHN, 6606 W oodlawn Ave., Chicago 37, Ill. (We still want ste-reo photos to illustmte articles if they w ill sll b'l'I'lit thel·n, and if they do we w ill print them. H owever, it ap­ pears that few of 01i1r authors remember 0'1£1' offer, and we shall have to use this interesting form of ph otography to illustrate m£r OWI ~ a'rticles ·in the fu.t 1/.1'e. ED.)

Editorial Distortion SIR : Figure 11 of "Distortion in V oltage Amplifiers" in the F ebru­ ary issue is quite interesting. The "H orrible E xample" shows about 0.1 per cent intermodulation distorti on at 1 volt output, while the improved circuit shows 10 per cent. A circuit diagram illustrating the good engineering practice needed to achieve this res ult would be enlightening. W . H , FROLICH, M. D., Steptoe Valley H ospital. East E ly, Nevada. SIR : I have read W . B. Bernard's article "Distortion in Voltage Amplifiers," in the F ebruary issue, with gl'eat interest, and with some di smay, particul arly in regard to the curve of Fig. 11 , page 55 . As I interpret the curve, the improved circuit gives very much more intermodulation distort:on 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 blowout 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 RONA LD L. lVEs, of the design and production techniques which have proved them­ 5415 Main St.. selves over the past fi fteen years-zirconium ' coating over the Williamsville 21 , N. Y. carbonized metal plate and pure barium getter to effectively ( W ell, we did it again. B~tt this time we can't blmne the dra fts­ man or the author. We rechecked the G1~ th o r ' s curve, and fO lmd absorb gas for the life of the tube-gold plated wire to minimize that we had made an errone01ts notation before sending it to the g rid emission. These are but a few of the major design improve­ draftsman. We bow 01£r editorial head in sha.me 1tntil the next ments in the 588!. sil'1!ilar e'Yror occurs. S eriously, we have requested 1'vIr. Berncwd to supply us with the improved cir c1.t.it to enlighten 0111' readers Tung-Sol produces the 5881 under laboratory conditions, to and ourselves. En.) a ssure peak efficiency and maximum uniformity. You'll fi nd 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: loads. So, if absolute reliability is essential in your audio circuits, The stripped-down, or utility model, circuit schematic ex­ hibited in conj unction with the di squisition on the Frudd Audio the Tung-Sol 5881 is a "must." O rder 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 Write for characteristics and performance dote little interest, anyway, to the intransigent audio enthusiast who invariably disregards trivia and introduces his own circuit modi­ TUNC-SOL ELECTRIC INC., NEWARK 4, N. J. fications with the utmost savior savior. My particular modifiea­ Sales Off ices: Atlanta' Chicago' Cu lver City (Calif. ) tion, a highly heterodox one, consisted in constructing the circuit precisely as diagrammed. Of course, as in any high-quality audio Dallas • Denver ' Detroit • Newa rk system, care in construction pays off in performance. I can attest Tung·Sol Plak.. AII ·Gla .. Soa lod B.am Limps, Ml nl ahr. that in assembling the circuit only the best components should Lamps, Signal Filihors, Plctu ... Tubes, Rad l.. TV Ind not be used. Speelll Pu rpose El ectron Tub ... I happened not to have available the pair of 211 's specifi ed. H owever, a search under the mattress (my habit of hiding my stock of component's in this fashion derives from the war years

8 AUD IO ENGINEERING • MARCH, 1953 ~~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 high-fidelity, delighted by the true-to-life reproduction. Soundcraft engineers are engaged in constant 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 you always associate with professionals. - demand Soundcraft Magnetic Recording Tape for the 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 recor~l. Wonderful Way to Make "Talkies" REEVES Soundcra't Magna-St':ipe* lets make sound movies as easily and inexpensively as silent films. Add sound to old silent films. Erase and SOUNDCRAFTcORP, change the sound any time at all! Dept. B, 10 East 52nd Street, N. Y. 22, N. Y. Magna-Stripe service is available to you at your photographic store. FREE! SOUND CRAFT BOOKLETS Ask your dealer about it. Complete information on Soundcraft 'T.M.R.S . Magnetic Recording Tape and Magna-Stripe. Yours for the asking - just wrife' during which electronic parts shortages drove the service shop next door to larce­ nous desperation) did turn up an old WDll. (That had been under the mattress since the first World War.) This proved to be CANNON quite satisfactory as a substitute for two 211's when operated Class AB~ in push pull with itself by means of an ingenious PLUGS get good reception 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 cent fidelity, quite unadulterated by any­ o SiRlES thing else. It is also the first audio system I have encountered that can be operated at X SERIES all hours without arousing the wrath of one's neighbors. With my previous installa­ ~.. tion, 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 coun­ try, I found this pnzzling and strangely disturbing. It has remained for the Frudd XK SERIES 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. O. Box 895, Rockland, Maine. Book Review FUNDAMENTALS OF AUTOMATIC CONTROL SYSTEMS, by G. H. Farrington. 285 pp. o SER\ES XKW-Bl SERIES New York: John Wiley & Sons Inc., $5.00. Automatic control system design is rap­ idly becoming the most far-reaching K SE.RIES branch of engineering, crossing the bound­ aries of all the other sciences. Although automatic control systems are not new, their study as a separate subj ect has only been begun recently. Audio engineers are most familiar with them in the form of feed­ back amplifiers and phonograph speed regu­ TElEPHONE RECORDER K SERlES 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-l09 familiarity with transient response studies using the Heaviside Expansion Theorem TElEYISION 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 servomechanisms, is not chised Distributors. In their great variety of M 1 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 trol1ed systems controllers, and their re­ be met. Cannon plugs are standard on leading specti ve 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 cbapters 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. R epre­ March 23 to 26, Grand are given, which might limit its use as a st:ntatives in principal cities. Address inquiries to Cannon Electric co llege 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 •• there's no roo... for douLt 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 engi~ neered 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. • MINI1UUM "DOWN TIME'-' AMPEX Recorders are designed for thousands of hours of con­ tinuous operation with minimum "down time," resulting in low maintenance costs and protection from sudden broadcast failures. • ACCURATE TUIING 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 stand­ ards. When you have an AMPEX, you have a machine built for years-ahead performance. IF YOU PLAN FOR TOMORROW, BUY AN AMPEX TODAY PIEX MAGNETIC RECORDERS

AMPEX ELECTRIC CORPORATION 934 CHARTER STREET • REDWOOD CITY, CALIF.

AUDIO ENGINEERING • MARCH, 1953 11 I

NEW LITERATURE • Electro-Voice, Inc., B u ch a n a n, Mich" will mail free upon written request copies of Bulletins No. 185 a nd No. 189, describ­ ing a nd illus trating E-V Aristocr at, Reg­ ency, and Baronet s peaker enclosures, as w ell as complem entary single and 2-way s p eaker systems. A lso listed and shown is t he E-V P eerage equipment console, to­ gether with a compreh ensive table of vari­ ou s ch anger s, amplifie rs, and tuners with YOUR PRODUCTION DEMANDS which it may be u sed.

THE EXCELLENCE OF • Minnesota Mining and Manufacturing Co., 900 F a uquier St., St. Paul 6, Minn. discusses u ses of "Scot ch" 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 u se of "Scotch" glass cloth t a pe with ther­ m osetting a dhesive in sealing, holding, and ins ulating where e levated t emperatures a re involved, This booklet is a n 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 A udio-Radlo-Television," is now issuing a h andsome, 24-pa ge three­ color booklet revea ling the design features, s pecifications, and pr ices of the company's extensive line of high-fidelity amplifiers, public-a ddress systems, FM-AM tuners, STEP PRINTING boosters, a nd a llied equipment. Irrespec­ ELIMINATES tive of your interest in a udio, this is a book you should have-truly one of the" CONTACT SHIFTS more worthy a nd complete listings of The sharpness of a print depends on q ua lity equipment to cr oss this desk In close contact between original and many months, priilt stock. In step printing at Pre· cision, the two films are a b. olutely • Hudson Radio &; Television Corp., 48 W. stationary during exposure. Timing 48th St., N ew York 36, N . Y. h as just re­ and effects are produced without leased a n ew catalog devot ed in i t s en­ notching original. tirety to sound r eproducing equipmen t. Intended essentia lly for music lover s and hig h-fidelity enthusiasts, the catalog is a complete directory of fine audio equip­ ment, including information on public a d­ d)'ess systems, intercom systems, a nd r e­ YOUR ASSURANCE OF placement part s. Available f ree upon re­ quest by m a il or in p erso n at Hudson BETTER 16mm PRINTS salesrooms. 15 Years Research and Spe­ enable us to offer service un­ • Wells Sales, 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 n ew Newest Facilities in the 16mm I6-page catalog. Of interest principally to aural. So organized and equip­ q ua ntity buyers, the booklet is designa ted ped that all Precision jobs are field are available to customers Catalog C-10, and w ill be mailed on re­ of the highest quality_ of Precision, including the most q uest. modern applications of elec­ Individual Attention is given tronics, chemistry, phys ics, optics, • Wasserlein Mfg. Co., Inc., 126 W. Cass each film, each reel, each scene, sensitometry and densitometry­ St., JOliet, IlL, is distribu t ing a n illus­ trated brochure titled "The New Way to each frame - through every including exclusive Maurer­ Solder," in w hich is descr ibed the rudi­ phase of the complex business of designed equipment-your guar­ ~nents of res istance soldering , as well as processing - assuring you of the antee that only the best is yours Its u ses for production and m a intena nce in industry. Als o contained in the booklet very best results. at Precision! are operating i11 struction s for us ing t he Wassco G lo-Melt r esistan ce soldering Our Advanced Methods and unit. R equests for copy should specify our constant checking and adop­ Bulletin No. 105-D. tion of up-to-the-minute tech­ niques, plus new engineering • ,Acmiola Distributing Co., 602 W. 52nd principles and special machinery St., New York 19, N . Y. lists the complete tine of Acmiola fi lm editing, film viewing, a nd sound r eproducing machines for p ro­ fessiona l u se in a n ew sales bulletin, AI! equipment is well described and effective ly Precision Film Laboratories'- a di­ illustrated. vision of J. A. Mau,rer, Inc., has 14 years of specialization j,n the 16mm • Equipto Division of Aurora Equipment ji,eld, consistently m eets the latest de­ Co., Aurora, IlL, r ecently announced an mands for higher qualj,ty and speed. 8-page catalog especia lly for the elec­ tronics industr y. Inclu,ded in the listings a re s uch items as work b en ches, chassis stands, sales counter s, steel s helving and bins, t est stands, a nd w a rm-up r acks. AU are priced. Catalogs are available singly for individua l u se a nd in quantity for jobber salesmen .

12 AUDIO ENGINEERING • MARCH, 1953 Easy, ACOUSTIC MEASUREMENTS

SOUND·SURVEY METER for Acoustic Engineers and Audio Enthusiasts

The Type 1555-A Sound-Survey Meter is a low-cost, instrument is extremely useful to sales engineersr 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. orbing 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 respopse curve so ob­ defects, enabling corrective measures tained will be very irregu­ lar, even in regions of fre­ * adjusting of cross-over net­ where the system works, and correct setting of levels response is actually fiat. Sig­ in multiple-speaker systems nificant characteristics, such * determining levels fo ti as a "notch" produced by an systems using tone-compen­ improperly adjusted cross-over sated volume controls network, may be completely ob­ scured. This effect is a result of rapidly changing standing-wave pat­ terns with changes in frequency. That is, combinations of in-phase and out-of-phase waves cancel and reinforce each oi;her at cer­ tain frequencies, causftlg abnormal "highs" and "lows" in response curves.

of the pocket-size Sound­ Survey Meter, measurements at each fre­ quency 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 and total room losses. three frequency character· Such results r epresent the performance of the istics, checks batteries - 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

A dmitlance Meiers * C oenial Elements * Decatk Capacitors Decade Inductors * Decatk ReBistori * Distortion Meiers Frequency Meiers * Frequency Slandards*Geiger Counters Impedance Bridges * M odulal.ion Meters * OsciUators Variacs * Light Meter. * Megohmmeter. * Motor Controz. Noise Meiers * Null DetecJ.oro * Precision Capacitor. Pulse Generators * SigrnU Generators * Vibration Meiers * Strobo8cope8* Wave Filter. U-H-F Measuring Equipment * V-T Voltmeters * Wave Analyzers * Polariscope.

AUDIO ENGINEERING • MARCH, 1953 13 Audio Photographer's 3 Super Standa rd Checklist Output EUGEN E F. CORIE LL':' Transformers

UDIO TECH N ICIANS and hobbyists rack with gleaming panel assemblies is are understandably proud of their not helped by a cluttet'ed test bench Aequipment and of course want to visible in the rear. photograph it for themselves and poster­ 9. Make sure all meters and controls ity. Unfortunately, even posterity won't are in their desired positions. If a VU be impressed if the pictures do not do meter is to be shown with the pointer at 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 fla shlight battery. If the shot is a close­ and while it will not make the .reader an up, make sure the channel and master expert, it may help him avoid the more gain attenuators and the VU range common errors of audio photography. selector are set for the VU reading de­ 1. Decide in advance exactly what sired. shots are desired and from what angles. 10. Clean up the equipment and the 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, 3. People add interest to pictures of racks and table-mounted cabinets show equipment, but be careful they do not up embarrassingly well on the finished steal attention from the console, custom prints, so take care of these beforehand. 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. T his usually do a pretty good job on metal rack sur­ calls for a tripod which will also avoid faces. ( But see item 25, just in the blurring often res ulting with a hand­ case . . . ) held camera. 12. Allow no smoking while the pic­ 5 . . Resist the temptation to use a wide­ tures are being set up . . . the smoke 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 wt. introduce considerable distortion. You to the photo ? If so, be sure the clock ap­ Ibs. do not want your turntables leaning at pearing in the picture shows the desired S·51O·F 2Ys ~2%-2X 2 . odd angles and bulgi ng at the top. time ... or get rid of the clock. S·526·F 4Ye-3J{6-2% 3 6. Some highlights are desirable. 14. Do certain elements in a close-up S·542·F 41~6-3~6-33{6 5X There's nothing like a lustrous sheen to require emphasis- for example, the re­ 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 a re some of the items that should 15. In close-ups, is tl1e appa ratus 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 fo r the obscure equtpment details you want to effective if it is framed by portions of stand out. If fl ash bulbs are to be used, the adjacent racks and turntables nor­ ne w test for highlights in the wrong places mally associated with it. 19'53 by holding f1 ooc1l amps in the proposed 16. What about shooting through con­ flash bulb pos itions. Attenuator dials trol room windows? Such pictures are Peerless and meter faces are often obscured by often spoiled by glare and multiple im­ Catalog the glare of highlights. If changing the ages refl ected from the inclined double Now in Stock lighting positions or angles does not panes. Make sure the windows a re 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 undes irable 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 El ectrical Products adjustment of lighting, and careful from unimportant surfaces like check­ cropping (cutting out undes ired border ered-tile foreground floors can be elim­ areas) with subsequent enlarging if inated by covering that portion of the A DI VISION OF Iilli.11 necessary. An impress ive 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. i * Major, USAF ; Radio T echnica l 0 /­ 161 Sixth Avenue, New York 13, New York I fi ce?', Arlned Forces In/or11la tioJI School, the latter must be used for effect, use k._, __.,,_ ... -.....;._ ... UM • • _~J Fort Sloc~tm , N . Y. (Contimted on page 70)

14 AUDIO ENGINEERING • MARCH, 1953 (

SILECTRON -CORES .•. BIG or LITTLE" ... an)/Juantity and any size \

For users operating on government schedules, Arnold is now produc­ ing C-Cores wound from 1,4, ljz, 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. 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 reqJ.lired-give you assurance of the highest quality in all gauges .• Your inquiries are invited.

waD 4363

AUDIO ENGINEERING • MARCH, 1953 15 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 ELL, THEY DID IT! After 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 Wat the Audio F air 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 10Glking We can't help taking our collective hat off to the boys all around Montreal fo r a 30 by 40 inch slab of half to on the \ i\1 est 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 in­ dicates 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 favor­ ite 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 ate 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 JE's readers who was con­ mittee which would purchase KISW broadcas.ting 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 KISvV advertiser, and money raised by the C0mmittee 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. i8-inch lBritish woofer with a free-air cone resonance Listeners can join the Committee by mailing their of 27 cps. With a port area of S4 square inches- dimen­ subscriptions in care of the station. If KISVv is worth sions being six by nine inches-his enclosure exhibited the' price of a one-dollar mGvie ticket per month, listen­ two resonant peaks concert ticket per month, they are poured around asbestos cement-board forms, and with asked to send $36 or $48. The first two dollars will be the front panel of one-inch slate. used fo r a subscription to the monthly program maga­ Nothing was wrong with this installation-except zine-or a renewal thereof-and the balance .goes into that our reader obtained a new position in Montreal, a fund to be used to purchase broadcasting time. nece$sitating the sale of the Vancouver house. Removal Many music lovers would welcome an opportunity to of the enclosure would have inv01ved '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 H~-il1lch woofer was unthinkable, as we would all this type throughout the country. it is probable that agree. some of the financial pr0blems would be alleviated. We Therefore, using considerable ingenuity, this reader shall watch with interest the results of this plan.

16 AUDIO ENGINEERING • MARCH, 195'3 ... it comes to you in the subtle shading of a piano . .. in the clean brilliance of violins, the purity of a Rute. 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 adds a Rood 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 tha t are released for your enjoyment when you use quality components by P·ickering. / ..

PICKERING COMPONENTS 61Jn Uw6e who canlhea4IUw ~~~

PIC Ii E R I NG and ~ompany~

• Pickering High Fidelity Components are available through leadil1gRadio Parts dis­ tributors everywhere; detailed literature sent upon request. Address D epartment A 1

Oceanside, L. I., New York

AUDIO ENGINEERING • MARCH, 1953 17 "Check your air, Sir 1'~

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 ~ 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 team 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

Improving felephone service for America provides careers for crealive men in mechanical engineering 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 re­ -sistance and capacitance across the pickup on the over-all frequency response.

U DIO SYSTEMS DESIGNERS and users ducers, at certain frequencies, two or are always greatly interested in three playings may make a particular A frequency response; in fact, one band un fi t for further use. The mechani­ might say that they are obsessed with cal im pedance of mphonograph record. This rec­ converted to electrical energy. This, for ured is an amplifier it is a simple matter ord may ce an ordinary "frequency" lack of a better term, might be called to achieve great accuracy. As soon as record, a "glide-frequency" record or the "mechanical response" of the pickup. a transducer is involved, however, the a "sweep-frequency" record. The usual This response curve must be added to measurements become much less reli­ . frequency record consists of a number the electrical response about to be dis­ able, although hardly more difficult to of bands of discrete frequencies recorded cussed to ·give the complete frequency make. at what is hoped is a known amplitude. response curve of the reproducer. The glide record traverses the indicated Transducers frequency band at a slow rate, covering all of the freq uencies between the start­ Electri.cal Response For one thing, absolute gain has no ing and the final one. The sweep record meaning in transducer measurements. does the same thing, but at a rapid rate Fl:g1we 1 gives a very close approxi­ It is necessary to settle arbitrarily on a (usually about 20 times per second) so mation to the equivalent electrical cir­ definition of gain in order to compare . that an oscilloscope can be synchronized cuit for a magnetic pickup connected to transducers. For a phonograph pickup, to the sweep rate and the amplitude­ an amplifier. for example, "absolute gain" might be: frequency characteristic observed di­ The useful signal voltage is that ·de­ microwatts output per centimeter per rectly on the screen. veloped across R L. second r.m.5. velocity at the stylus tip. Each of these records is useful-and Even this is incomplete, though, since each is subj ect to considerable error. Network Equations no allowance has been made for the The fixed-frequency record is the only mechanical impedance at the stylus tip. one which can be calibrated, and this The total impedance in the circuit is: Whenever such definitions are pro­ procedure must be carried out on each posed they usually meet with an apa­ pressing if precise results are to be thetic reception for one or more of the RL( -de) obtained. The general willingness to Z t = jroL + Ro + . following reasons: 1. It is hard to agree rely upon frequency records indicates a RL_-J­ on units, since metric and English units lack of awareness, on the part of the . roC are all mixed up in the recording busi­ user, of the many possible chances for which becomes: ness. 2. Most engineers feel that pickup error in this method of measurement, efficiency is ·not important, since ampli­ yet what is the poor fellow going to do? ( RaRI. + ~ ) + j ( RLro' L~~ RaRL) fier gain is cheap. 3. Absolute gain meas­ About all that is possible is to purchase urements require much care and ·some Zt= . a· well-made record which shows a J I·elatively expensive equipment. "flat" light-pattern and to discard it as RL- roC * 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 in the circuit is paclbve component; the frequency re­ 10 0K sponse may be calculated from Eq. (2) . 90K / ~=/= Figwre 2 shows the results of such cal­ J Zt j culations for a pickup of 150 millihenries 80K V RL- wC '" inductance and 600 ohms resistance. It %'" 70K will be seen that the response becomes 0 V L ) .( R LW'LC -RoRL) ~ SDK ( RoR[. + C + J wC asymptotic to 6-db-per-octave roll-off ..z / at the high frequencies, and this fact ~ SOK may be used to advantage in equaliza­ - 401< / The voltage across the parallel combina­ '"-' tion of C and RL is /Z8 where tion circuits for pre-emphasized record ..z 30K J =>0 characteristics. It will further be noted z 20K - j RL that the low-frequency level of the vol­ V (de ) 10K tage output is uniformly attenuated be­ 0 100 .200 .300 .400 .500 .600 .100 .SOO .900 Zs = ( 1 ) cause of the resistance Ro of the pickup COIL INDUCTANCE · HE NRIES RL- j wC coil. This constitutes a practical limit Multiplying / by Z s, the signal voltage to the amount of attenuation which can Fig. 4. Nominal impedance of a magnet io across the load becomes: profitably be done with only a resistor pickup as a fun ction of coil inductance. E out = R L + jwRL'C [RL + Ro - RLW'(2LC + RoC)] + j [W(RL' C + 2RLRoC + L - RL'W'LC)] (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 R L have a high ratio of L to Ro, more high­ lead grounded, it is the sum of all the frequency attenuation can be achieved E out =R L+ R 0+ JW. L (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 Fig'ure 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 Jt f L. It is not so easy to of L to R o. L is 0.472 henries and R o 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 wi ll 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, th e load resistance for significant than the absolute value of C. has no control over R o 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 Jt fLat Pract ical Values of Capacit ance TAB LE I 00 = 1.25 x 10" (approximately 20,000 Inductance and Resist ance of cps). At this point the electrical re­ The Miller-effect capacitance of vari­ Typical Pickups sponse will be down 3 db. Figwre 4 ous input tubes is listed in Table II. The Pickup L RG shows the nominal impedance as a func­ tubes indicated are those usually en­ tion of coil inductance. This illustrates countered in phonograph preamplifiers Audak L- 6 0 .7 80 Hy. 630 ohms used for magnetic pickups. C. E. RPX-050 0.470 Hy. 370 ohms clearly how the pickup with 780 milli­ Pickering 140 henries inductance can have a nominal The input connection to the preampli­ & 120 0.150 Hy. 600 ohms impedance of 0.1 megohms, although its fi er 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 vari­ ous 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 appreciaWe ca- connected to an amplifi er without hav- [Coati1tued oa p'.age 60]

+2o r-'-~rrrnl ~--rr-'-'-r~rn----r-'-'-rrrn~~' I + 1 0~+-~~HH+---~-4-4~++H4----~+-+-~rH+---,

I--I-+-I-I-I-H-I-- -I--I-I-I-·HH-I----I--\·LOAD RESISTANCE - ILOAD ' ~ESISTANC E O ~ ~~~~~~~~~~~~~~~~~~tE~20000~a~OO I-'=~~~~~~~~~~EESl~~E:~~Cf~-r-. t5~30~ -..r-..,...... r-. ~ 10 -10 ...... 1'. ~ :- 1--.J-;H-+-H-H___ 1- __ -- I-I---\--t-...... -\ r-.-P;..±-\+N~~ 1-+--Hf-+rH-j- ---j--r- - \ -++\-H--- \ --I-I-I-' H"'\o...4~ 3 ' X - 201-+-~~~+---~-I-I~~~----I-+-+-~rH~1~,~ CALCULATED FREQUENCY RESPONSE "' -2or-i-~rrHi+--G. -E~. rC-A~R-T R~ID~GrErr~--~~+-~~~+-~.,~ -\- 0120 WITH VARIOUS LOADS # ----\- +-+-If-+H4t----'''I j 472mh I R, • OHMS - :30 L 21S0 mh Rg a60e OHMS I i 370 t-+-I-If-+I~II-I-I ---I-~I .-~I ~I+I ~-+-~~#__~ II I ,. , II III II I III 1000 1000 FREOU ENCY I N CYC L ES PER SECOND F REOUENCY I N CYC L ES PER SECOND

.F ig . 2 (l eft). Curves showi ng t he frequ ency response of a Pickering D120M pickup with various resistive loads. Fig. 3 (right). Frequency response of . GE RP X-OSO pickup with various resistive loads.

20 AUDIO ENGINEERING • MARCH, 1953 A Power Tube Figure of Merit

WARREN C. BENDERl"

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.

T IS CUSTOMARY to define figures of while a standby fo r almost a generation, It must be remembered that the Tube­ merit in order to have a numerical suffers from the need of a special fil a­ Manual figures used to derive these I 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 fil'St 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 A.B, 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. A ll 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 fi gure 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 i$ significant to that this is a realistic representation of pull tubes. Also since home amplifiers note the high' fi gure of merit obtained the situation. The high power sensitivity are considered, only A and AB, opera­ by class A 6L6's which are very com­ of beam power tubes makes the applica­ tion are tabulated. monly. used. tion of larger amounts of negative feed­ The value of the fi gure 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 beam power tubes. Class A 6L6's at 10.5 of tube. watts output have a figure of merit of It is in teresting to note the correlation 1.75. The figure of merit of class A between high figures of merit and popu­ where 6K6's at 9.8 l'atts is only 1.54. larity of application. The use of this If operation into ABo is allowed the figure of merit enables a numerical com­ := Figure of Merit F figure of merit increases markedly, al­ parison of the desirability of various P := power output in watts though this increase is attended with tubes under consideration for a given D := distortion at rated output greatly increased difficulties of driving amplifier. If it is desired to evaluate new RL:= load impedance in thousand ohms power, power supply requirements, etc. tube types or other operating points, the Eo := peak grid driving volts. Fixed-bias 6L6's with 47 watts of out­ calculations to obtain a figure J)f merit The available power appears in the put power have a figure of merit of are straightforward and easy. Thus it numerator of the fi gure 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. Con~ersely the peak grid driving volt­ TABLE I age and the load impedance, which is a Figure of Merit function of the internal impedance, ap­ pear in the denominator. Thus, the fig­ Triodes Class Bias Voltage Power (watts) Figure of Merit ure of merit is an index of the power 2A3-6S4 etc. ASI Self 300 10 1.22 available as modified by other factors 2A3-6S4 etc. ASI Fi xed 300 15 3.94 which make the use of the tube more or 6AS7G A Self 250 13 0.83 less desirable. The larg.er the figure of 6AS7G A Se lf 200 11 1.47 300A A Self 450 35.6 4.90 merit the better is the tube. 4.5 4.42 A number of values for commonly KT66 ASI Self 250 KT66 ASI Se lf 450 14.5 4.38 used tubes is given in T able 1. 807-1614 ASI 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 Class Bias Voltage Power (watts) Figure of Merit of fixed bias. However the choice of bias Tubes method must depend on the decision of 6V6 ASI Self 285 14 4.45 the designer as to the return for the 6V6-6AQ5 ASI Se lf 250 10 3.17 extra trouble of providing fi xed bias. KT66 ASI Se lf 250 17 11.30 Within this group of tubes are many KT66 ASI Self 450 30 5.05 6L6-5881 A Self 270 18.5 9 .06 differences which are not reflected in the 9 .80 common fi gures of merit. The 2A3, 6L6-5881 A Fi xed 270 17.5 6L6-5881 ASI Self 360 24.5 4.58 6L6-5881 ASI Fi xed 360 26.5 8.78 * 62 Parl~ St., T enafly, N. I.

AUDIO ENGINEERING • MARCH, 1953 21 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 1 +1 ~ given transition frequencies and I I .I.~ I I . I I I II I V rates of boost or cut have been ex­ --- SPEAKER RESPONSE (PRESSURE) 1--- TONE CONTROL RESPONSE (VOLTAGE) r I , tensively discussed in technical litera­ r- -- RESULTANT SPEAKER OUTPUT ' L---- +10 (PRESSURE) ture. Little has been written, however, • .' I),~ about considerations involved in the z /' seiection of the response-curve param­ ~+ 5 eters, which sometimes seem to be Fig. 3. Resultant fre­ z .A 7 \ quency response of o fI chosen more or less arbitrarily. While Ij'" , ~ ,. . an ~udio system us­ ~ " flat" power amplifier stages are care­ '" 0 . ing a commercial '" -..-' , fully designed for an audio-frequency speaker in the $50 , response which is kept to a maximum class and the treble ~ , rv4' ~ -~ I"" random deviation of a fraction of a boost of (A), Fig. 1. Iii '"o decibel, improper tone compensation '" , (either manual or automatic) in the '"~-1 0 I same amplifier may introduce, or leave §! uncorrected, very large inaccuracies of • -1 ~ r, 20 • . , . 20000 frequency distribution relative to the 100 1000 10000 perceived original. These inaccuracies FREOUENCY IN C YCLES PER SECOND have on occasion completely oyer­ shadowed the benefits of the above-men­ tioned careful design, and have become a primary factor in determining over-all volume level. T he 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 fi xed equalizers does T he 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 have been exactly determined by his audio ampli fiers is a two-control, con­ ING. problem. In contrast a tone-control de­ tinuously variable system. This allows 1 The transition frequency is the inter­ progressive cut or boost of either bass section of the theoretical linear· slope of the signer must furnish the means for 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 t·eference frequencies at which axis-see Fig. 5. either provide a complex control system the response curves begin their slopes.

+25r-~+-~~~--~- 1- 1~~+++ 1 ---- '~+-+4 ·~1- 1 ·· r--- +2°l::::t:~I::t±tH----r--Hrtttthr---t-++titttt----1

20 , ••• '00 '000 20 I • • • "0000 FREOUENCY IN CYCLES PER SECOND

Fig. 1. (A), Voltage response curves of a typical commercial tone control circuit of the R·C type, maximum positions. (8), Voltage response curve of a commercial tone control circuit of the L· R-C type, maximum positions.

22 AUDIO ENGINEERING • MARCH, 1953 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 fide lity to the perceived original, paragraphs devoted to bass boost. of frequencies, bes ides being of fal­ 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 head's, but -also occur in versal practice for dual tone controls revolves about the question of what the co upling circuits in audio or inter­ to use approximately the same tran­ controll er must be equipped to compen­ mediate-frequency amplifiers. sition freq uency region, usuall y at or The worst offender in a given system below 1,000 cps, for both bass and sate for. In the fo ll owing discussion it is ordinarily the loudspeaker. In Fig. 2 treble variation. Figtu-e 1 shows the will be 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. thoug h the performance represented by these curves will vary greatly under different acoustical conditions the 111 1 I IIT IIIII graphs may be taken as indicators of II o. SUPERIMPOSED REFERENCE LEVELS - a general trend. T here is one feature , 50,,1'1011' OF SO AND eo phon CURVES OF which all may be :seen to have in com­ 0 FLETCHER - MUNSON EQUAL LOUONESS - CONTOURS. mon, and which is character istic of the 1'" great majority of cone loudspeakers I • with high-frequency droop; the fre­ 0 2JO. , quency region of the first two octaves Fig . 4. The 50- and above 1,000 cps, far from being attenu­ I "'- :dI SO-phon equal loud­ ..... f-..U '-, ness contours (from ated, is accentuated (because of the 80 phon. Fletcher and Mun­ new resonances introduced by cone '. son) superimposed. break-up) , and treble droop does not 0 - 20. ~ .~ , begin before 4,000 cps or higher. This fact has a significance beyond the ob­ • vious implication concerning compen­ sation for speaker d efic i ~ncies . Any losses in the first two treble octaves , , " . . . '0000 which are likely to be met with from " . 100 1000 10000 FREQUENCY IN CYCLES PER SECOND other causes will probably be compen­ sated 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 rather 1. Compensation for treble deficiencies and 16,000 cps, frequencies which may sharp cut-off somewhere between 4,000 be taken as nominal limits of hearing ill associated reproducing equipment. 2. Compensation for treble defici encies and 10,000 cps. When this regul ar droop under average conditions. Since the in program material. does not conform to the desired record­ perception of frequency, li ke that of 3. Compensation for di scriminatory ing characteristic further compensation amplitude, closely follows the Weber7 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 equali zation, and the recommended quency spectrum is its psychological treble boost has on occasion been con­ ci rcuits or necessary data for their de­ mid-point. T hus 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 frequenci es 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.:~ , , '.' rr V· I A :f ~ ~ • ii: j't-' A - 111 ~ 10/1 '"z Z ...;r-- '"o 0 \ .. V ~ II!'" Ii - 0: II J 1-+i'+lI+++lH---+ --- 0' SPEAKER :...! -l--l--++1Ij~IIl---l , 'I Ii --- 12- SPEAKER m I--li--Ir-I+~f+---I- ---- 10' SPEAKER [f-l---I---,+-++lNIII---I ~ - .- 12' SPEAKER 1 I-+-r-I+~f+---t- == 2-1~' SPEAKERS i I J 11 Ii II II :w III III Ii II II It • II I II \.1 . ,. '0000 "0000 " 100 1000 100 1000 FREQUENCY IN CYCLES PER SECOND FREQUENCY IN CYCLES PER SECOND

Fig. 2, (A) and (8). Pressure response curves of three commercial speakers in a price range of $20 to $150.

AUDIO ENGINEER ING • MARCH, 1953 23 for correct crystal pickup equalization the compensation will not be used. This B+ 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. T he operator droop to set in before 4,000 cps or so. of the set may be impressed with the Even AM broaicast 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. Briti sh manufacturers lean towards Treble deficiencies in program ma­ hi gher 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 JE 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/or felUrth treble oc­ simplicity of the single network is one 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 quantita­ the maximum, and it will prove ample spectrum is or has been treated by rec­ tive study which compares the frequency fo r 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 th e reverberation 12 db of maximum boost at 13,000 cps, the treble-cut control. If the setting for time vers~ts frequency relationship-may including about 3 db of boost at the minimum treble furnishes close to 6 db be a factor requiring tone compensation. I'eference frequency itself. These char­ of attenuation per octave from a transi­ Refel-ence 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 subj ective 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 transi tion a single R-C network. Transition Rate of frequency for the sake of increasing the Records Frequency Boost (cps) (db/ octave ) amount of boost available at the upper Treble Attenuation end might prove satisfactory if it were AES Standard Curve 2500 6 not fo r the marked tendency of loud­ Treble attenuation is required for: Columbia 78 & 33 1/ 33 1590 6 1. Compensation for varying treble RCA 783 1000 2.5 speakers to emphasize the frequency re­ 3 pre-emphasis in recording. London ffrr 78 _ 3000 3 gion of the first few thousand cps. A 3 transition frequency of 1,000 cps or 2. Reduction of record suface nOIse London 33 1/ 3 3000 6 and high -frequency distortion. EMI 78' none lower may cause treble boost 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. and needed boost at frequencies above 4. Tonal balance against a thin bass. Settings of the treble control which yield 4,000 cps may carry such a penalty that less than max imum attenuation will also, Treble pre-emphasis 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." 1. AcOtts. standard, either of transition frequency equalization for some elf the records Soc. Am., 7, p. 134, Oct., 1935. or rate of boost, to which recording with more gradual pre-emphasis slopes. The desirability of equal ization for treble recording characteristics prior to the tone control is emphasized by the differences between the transition fre­ II - quencies of some of these recording +20 f--p ~). I curves and the frequencies at which the ~~OCl' equi pment deficiencies previously dis­ +15 cussed introduce treble losses. For ex­ .... ",~ • +10 ~ ample, an improperly eq ualized disc ...... Fig . 5. Suggested ~+ 5 which has been recorded with a given '~t::- tone control fre­ , 0 kt:" treble characteristic can present an un­ FT FT quency chamcteris­ ...... r-- ~T N satisfying choice between shrill and ~-5" ~ - tics, con t r 0 I s at muffled reproduction, because the tone ./V r-:: .. maximum positions . g-10 [Contimled on page 68J ~ ~. . -1 5 ~ \.f."\ 3 Paul W. St. George and Benjamin B. -20 I I ~ • Drisko, "Versatile phonograph preampli­ r'i I II fie r," AUDIO ENGINEERING, 33, p. 14, I I I FT · TR AN SITION FREQUENCY March, 1949. 4 ,...... '0000 D. T. N. WiIIiamson, "High-quality 100 FREOUENCY IN CYCLES PER SECOND amplifier modifications," W 'ireless World, 58, p. 173, May, 1952.

24 AUDIO ENGINEERING • MARCH , 1953 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.

HE TREATISE ON SOUND whose title The Collection and Transmission of Sound J?age is here reproduced was written DE Acoustical ear-tubes ... work on the TIII 1693 by Caspar Ringelmann, NA TURA E1' JURE pril]ciple 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. Although more profound work in the nc (See Fig. 2.) By listening to a sea-shell theory of vibrations had already been or large jug one can even hear the re­ performed by Galileo and Newton, and sidual sound produced by the otherwise although Bacon's N ov ·~tm Organum had SONI, qUIet ambient air. outlined standards of scientific method In Illuftri Univcrfitatc Along this same line of reasoning, it is possible to construct a building so that which Ringelmann did not always meet, CHRISTIAN-ALBERTINA, if a person we·re in one central place he the description of contemporary acousti­ Sub Pra'iidio PIr; Ampliifillli e5 CoH(idt:"fimi could hear everything going on through­ cal design makes absorbing reading, and out the entire building. is often prophetic of modern devices. . Dni. SAMUELIS REYHERI, Kircher (in Photlltrgia Nova, 1673) Following are selected passages from Jeti, Codicis nec non Mathcmm. discourses on some Acoustic devices the treatise, translated from the Latin Superior. & Inferior. Prof. Ord. &c. of his which will enable one to carryon (the language then standard for all Pra:ccptoris fui a:tatem dcvencrandi , a conversation from one room to another Dit 27. Maji,t/JIIJ; M DC XClll. scholarly work). inside of a house. (See Fig. 3.) Or, out­ dilflUtabit doors between two distant places. The Nature of Sound and Hearing CASPAR RINGELMANN Oldenb. Wdlphal. Construction of an Artificial Mechanism Sound is an oscillatory movement of gtluH"/[.1rDrllm, the air activating the ear locally. Typis Joachim. RcumaMi, Acad. Typogr. The inner ear has the sensory func­ It will be noted that the device de­ tion. The outer ear collects the sound scribed below substantially constitutes and transmits it to the inner. the input system of an acoustical phono­ 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 bodies in motion. Thus, air movements Ringelmann, of Oldenburg, Westphalia, who stretched across the horn's throat, and set the tympanum of the ear in motion; "will dispu te" (defend the thesis) on May 27th, a mechanical device attached to the this in turn moves the Hammer which 1693. diaphragm. strikes the Anvil. From here on, the mo­ tion is carried by air pressure differ­ The term "artificial ear" refers to a ences. (Note,' this is inaccurate; the device which is an actual working model sOlmd is actually propagated through the 28 CAP.X.Demodo audiendicompofito. of the human ear. (Figure 4). It may be cochlear fluid.) These internal pressure used to demonstrate the mechanism of differentials act upon the auditory nerves the hearing process, or in the case of which transmit them to the brain. auditory deficiency, to bring about a Vitruvius1 well explained the nature certain degree of compensation. of sound where he says: "Sound pro­ 1. Make a little ring of metal and ceeds outwardly in a series of increasing form the leftover end-piece into a short circular movements. It is as though we appendage. Let the very end of this were to throw a stone into a pool of appendage be the Anvil (c). placid water .... Starting from the cen­ 2. Cover the dng with a Iightly­ ter the circles become larger and larger." stretched membrane. 3. Glue or fasten onto the membrane the * Princeton, N. I. 1 A classical Roman architect and writer. Fig. 2. Ear-tubes for voice communication. [ Continued 01$ page 56J

158 PHONURGIK LIBER J. SECT. VII. !lO PHONURGL£ LIBER J. SECT. IV.

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

AUDIO ENGINEERING • MARCH, 1953 25 ,

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 .

N THESE DAYS of intense competition was cut through to the main studio and material fed on either of these circuits I in 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 alre.fl.dy treated for sound ically removed from the circui~ :when television, it often becomes necessary for isolation. The cost for this work, includ­ the patch cord is inset·ted. Figure 1 radio 'stations to effect every poss ible ing painting the window frame was giv:es the layout described above and economy . in their operations. Yet the engineering department is frequently $88.00. Nothing more was spent on this shows the tape recorder setup outlined in the next paragraph. faced with increased program ·and re­ room except for varnish to improve the 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 quate to meet the demands of the pro­ field simultaneously. These field ampli­ the 22D amplifier. This recorder is equipped with a high-impedance bridg­ gram and commercial departments. fiers are Western Electric 22D models. ing input and a 600-ohm output, both There a re usuall y enough studios One of these amplifiers was installed on available, but a serious lack of studio of which appear on screw-type terminal a small, badly scratched, desk which was strips. For convenience in removing control facilities is generally encoun­ given a coat of commercial-looking tered when numerous auditions, re­ and replacing this unit, small connect­ green paint. Four lengths of flexible, ors were installed at the rear of the hearsals, and recordings are scheduled, shi elded, microphone cable were fed in addition to the program "on the air." chassis. The bridging input is connected Studio control equipment is costly, so through the wall and terminated in across output # 1 of the 22D amplifier if anything is to be done to improve the microphone input receptacles mounted and the 600-ohm output is fed to the situation it must be on the basis of in Wiremold boxes. The control room 3D-ohm microphone input channel #4 making the apparatus on hand do double ends wet'e terminated in connectors through a 600-to-30 ohm, 60-db pad. suitable for the microphone inputs of duty and of using any spare or obsolete This provides for recording, through pieces, modifying these units to perform the 22D ampli fier. Two 600-ohm out­ the bridging input, any program mate­ puts are available on these amplifiers. a satisfactory broadcast service. One rial going into the ampli fier, and to feed such situation as outlined above was F lexible cables were connected to these to the amplifier, through #4 mike chan­ overcome in the following manner. . wi th the other ends terminated in nel, any tape recording played on the Adjacent to one side of the main twist-lock connectors. These connectors recorder. In this way, three studio studio was located a small room, 12 by plug into receptacles mounted in \'Vire­ microphones and the recorder can be 7 feet, which was being used for office mold boxes and installed on the wall fed simultaneously into the amplifier or, supplies. Arrangements were made to near the desk, from which two shielded if no recordil}g is played, four studio pairs are taken' to the main jack panel house these supplies in other parts of microphone channels are available. the premises and a 48 by 30 inch window in the master control 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 wt Ave., N.W., Washington 6, D.C. By means of patch cords, program and they ai'e, therefore, easily inter-

TO TAPE hUCROPHONE CHANNElS RECORDER

OUTPU., T 600~ TO MASTER CONTROL

HIGH IMPEDANCE INPUT

TWIST·LOCK RECEPTACLES

Fig. 1 (left). Diagram showing interconnections between WE 220. Remote Amplif.i er. and a portable tape ~eco.rder to ~r?vide extra studio control facilities. Fig . 2 (right). Block diagram to show connections for transCriptIOn turntable and mOnitoring amplIfIer and speaker.

26 AUDIO ENGINEERING • MARCH, 1953 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 I:-CfT~I------ing system is given in Fig. 2. Con­ monitoring amplifier as many published I ____ " I ----- 5 nection between the preamplifier and circuits would be satisfactory. However, the 22D amplifier is shown in Fig. 3, one requirement of the amplifier used I = I 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. sc.ription equipment and 220 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 turntab1e 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 are 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 I-mil stylus for micro­ when required ill' 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 preampli'fier 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.

March 23-26-INSTITUTE OF RADIO ENGI­ PONENTS SYMPOSIUM. Presented through SHOW AND CONVENTION, sponsored NEERS, convention. Waldorf-Astoria Ho­ cooperation of AlEE, 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 SHOW. Grand Central Palace, New York ACOUST·ICAL SOCIETY OF AMERICA. War­ AND SOUND EXPOSITION, combined with City. See page 38 for details. wick Hotel, Philadelphia, Penna. Fea­ the CHICAGO AUDIO FArR. Palmer House, April 28-May I-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 VISION BROADCASTERS' convention and N. J., on May 8. of the AUDIO ENGINEERING SOCIETY, and 1953 BROADCAST ENGINEERING CONFER­ THE AUDIO FAIR. Hotel New Yorker, ENCE. Burdette Hall, Philharmonic Au­ May 18-21-1953 ELECTRONIC PARTS New York City. ditorium, Los Angeles. SHOW. Conrad Hilton Hotel, Chicago. October 15-17-AcOUSTICAL SOCIETY OF April 28-May 1-1953 ELECTRONIC COM- August 19-21-WESTERN ELECTRONIC AMERICA. Cleveland, Ohio.

AUDIO ENGINEERING • MARCH, 1953 27 /' The Columbia "360" PETER C. GOLDMARK*

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

T THE END of the last war, one of the programs facing the Laboratories A 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 reproduc­ tion ,vhich, 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 in­ volved creating the mate for the LP • recor,d 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 com'pact, entirely self-contained, reason­ ably 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 ulti­ the music originally recorded. Sufficient it into 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 desired end effect could best and the instrument has adequate re­ ing virtually everything recorded on the be described as realism. The Columbia sponse between 50 and 12,000 cps. Most LP record, the Columbia "360" has been "360," shown in Fig. 1, which is the records do not contain much usable in­ developed. first one of a new series of music re­ formation below 50 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 foll owing paragraphs some technical can-unless properly controlled-pro­ details regarding the "360" will be dis­ duce considerable rumble and surface • Vice-Pr e ~ident in Charge of CBS Lab­ cussed. noise. oratories Divlsion, 485 Madison Ave., New Realism in music reproduction in­ Effects such as distortion and inter­ Yark 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 concen­ trated on the most important processes involved in the translation of electrical impulses to sound waves. The phono­ graph 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 fo und 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 instr~me nt directed straight at the listener as has been the practice to • date. \Ve fo und 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 cabi­ net, as shown in Fig. 2 sound is now

28 AUDIO ENGINEERING • MARCH, 1953 developed; the arm, made of metal, pro­ duces a slight resonance of around 50 cps which plays an important role in the over-all frequency response of the sys­ 1- ·-1- tem. The cartridge has been developed with the Sonotone Corporation and uti­ t-:-.,..-+.~=-'."-t-t-N:I-I ·· I- c- 1- li zes a ceramic element. A rotating 1- needle assembly, Fig. 3, carries two sap­ phire points back to back, one with a radius of one mil and the other with a radius of three mils:\Needles assembles containing a diamond stylus for LP rec­ ords will also be available. The fre­ quency response of the cartridge-and­ Fig. 5. Measured acoustic response curves, arm combination looking into a load of compared with electrical curve of Columbio 1.0 meg. and 100 !1!1f, is within a few db 103 test record. Curve A is response with of the required reproducing characteris­ maximum treble; B is with minimum treble. tic when using the Columbia No. 103 Solid curve represents the test record. Fig. 3. Underside of the tone arm showing the test record as signal source. The car­ tridge compliance is of the order of 0.9 rotating stylus assembly in the cartridge. The P. P. 35L6 stylus is rotated to change from LP to 78. x 10- 6 cm/dyne and the voltage output, ~-TK ~ MODEL MODEL39 '" ~ 12AX7 I 59 using the Columbia 103 test record, is i.M. radiated practica11y all around the in­ 35Z5 approximately 0.5 volts at 1000 cps. The i. M. >0- rr strument (hence the name "360") and arrives at the listener after it has been stylus can easily be changed by any lay­ 20 man by raising the arm, lifting out the A'RESISTOR LOAD bounced around in the room, resulting I- • 1.6 OHMS entire stylus assembly and replacing it t- I in a mixture of many different phases B-SPEAKER LOAD with a new one. z 15 J II and amplitudes. 0 , ~ 1/ 8 The "360" phonograph has a loudness 0: The Record Compartment 0 A control instead of the usual volume con­ :;; The record itself is played in the trol, and it has a treble control instead c 10 I middle of a sealed sound chamber rep­ of a tone control. At every setting of the ... .1 II ~ II resented by the solid half-inch-thick loudness control, the tonal balance is ffi" cabinet walls. Every available air space automatically changed to give optimum .. 5 II reproduction for that given sound level. V / within this enclosure has been utilized l- l- to create the desired sound and the air The treble control influences only the .... I- 0 ..... pressure produced by the speakers has very high frequencies; for instance, the 1.0 1.5 2.0 2.5 to be preserved during playing by keep­ difference in output for the maximum VOL7S RMS ACROSS LOAD ing the lid closed. If, while playing rec- and minimum treble positions is 12 db . ords, one were to lift the top even a at 10,000 cps, but only 3 db at 3,000 cps . Fig. 6. Intermodulation distortion vs. power trifle, the oass 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 betwee·n 85 and 90 cps. Nevertheless, the sound pressure curves of Fig. 5. there is no acoustic feedback between the over-a11 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 con­ ventional way, the player was set up in 7500(TONE) a room, the acoustic properties of which approached home listening conditions. A large number of sound pressure curves were derived using different dis- [Conti1~ued 0 1~ page 59)

52S8 H P PP 3SL6 2000 RO-'\I 12AX7 g " 00S10RI10N ANALYZER - '0- 3 SZ5 $r -~-

C.$O'\J SPEAKER 15 10 r- LOAD I- 0 ·10000'\1 SPEAKER ,/ LOAD ~ C Q I/.: ... 5 z ~D ~ ..... ~ - '= 1:::== 0 - c 1.0 i.5 2.0 2.5 VOLTS RMS ACROSS LOAD A· 400'\1 SPEAKER ~10 I- LOAD ~ I- B· 400""' RES ISTOR ./, TUBE LOCATION ~ LOAD · 1.6 OHMS Aif/ Q A ... 5 NOTE ~ .- va REVERSE PHASING OF SP'EAKERS WI LL " I-f-::: ", ,. ELECTRICAL GROUND CAUSE lOSS OF BASS. ~ 0 9 8 REVERSE PHASiNG OF FEEDBACK WiLL 1.0 1.5 2.0 2.5 ~ CHASSIS GROUND BACK OF CABINET CUTOUT CAUSE AMPLIFIER TO OSCILLAT E. VOLTS RMS ACROSS LOAD

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

AUDIO ENGINEERING • MARCH, 1953 29 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.

N THE PRECEDING ARTICLE, the writer capacitors in the dividing network, the discussed the many practical and LIP ON SIDE OF HORN voice-coil impedance should be around I 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 .l·eproduc­ 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 nonnal 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 rat11er 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 sec«md assembly was built a shop which speciali zes 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, mel).tal 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 IS-in. tively expensive, and that this design out in a smooth exponential curve. speaker -and replacing it with a sturdy was economical. To meet all requir.ements, a throat 8-in. frame. However, a high-quality Having secured a suitable magnet opening of 40 in. square wurks 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 SOUl'ce a frame axis across the center. Then plot points so as to provide a large magnetic flux­ or "basket" for an 8-in. speaker. Re­ on it starting with the 40-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 l yg 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)4 in., and 10 in. or more would unit, be sure to cover the voice-coil jar 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 RIVET-S TO SPEAKER MOUNTING FLANGE 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 horR.

30 AUDIO ENGINEERING • MARCH, 1953 gao 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 40 x 40-in. square in the center of this circle and saw across the di­ agonals with a hacksaw, as shown. Drill two rows of Y

TIE BOLTS

Fig. 7 (left), Horizontal and vertical sections through the center of the speaker !lnit 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 Handbook of Sound Reproduction

EDGAR M. VILLCHUR":

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

Chapter 1O. Loudspeakers. (Part 1 )

OUDSPEAKERS are electro-acoustic de­ the diaphragm of a horn-type speaker, vices for converting the electrical FRAME makes immediate contact with the air Loutput of audio amplifiers into me­ into which it radiates sound. chanical and then acoustical energy. Modern loudspeakers are almost ex­ The Mechanical System of the Speaker clusively of the dynamic (moving-coil) If the cone and voice coil were mass­ type. The dynamic loudspeaker allows less and perfectly rigid, and there were the electrical signal to pass through a perfect freedom of motion for the voice coil which is free to move along its coil, an analysis of cone vibrations longitudinal axis, and which is sus­ 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 istics of the speaker "motor". Unfor­ magnetic material the static field exerts tunately for speaker fidelity, however, no force on it except when current the mass, elasticity, and friction of the flows. 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 pressure will set up imitative Fig. 10-1. Typical single-cone, single-voice­ cone. When the voice coil is forced vibrations, and 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 acous­ tical energy is increased by means of some type of acoustical coupler between • ~ ICOMPLIANCE. RIM SUSPENSION the speaker and room, such as a horn FRICT ION. RIM SUSPENSION or baffle. It may be seen that the first step of iillmm~.J~---~ COMPLIANCE, SPIDER the above conversion, from electrical to Fig. 10-2. Mechani­ cal system of a dy­ ~ mechanical energy, is exactly analogous FRICT ION. SPIDER rv !:; namic loudspeaker o to the action of an electric motor, where (ignoring air load) > current is passed through an armature I and electrical anal- MASS , VOICE COIL free to rotate in a fixed magnetic field. ogy. Figure 9-1 illustrates a typical di­ rect-radiator loudspeaker, so called be­ MASS, CONE cause of the fact that the cone, unlike • * COllt1'ibuting Editor, AUDIO ENGINEER­ ING.

mass and the spnngmess of the spider and rim suspension create forces of their own. The speaker mechanical system is a resonant source of sound in addition to an imitative one, and • when stimulated it tends to oscillate at 1-++-H-f-l,oIA-V_-lI/'-j-l-+Hd-tAIR LOAD MASS RESISTANCE- its own natural frequency independently of the controlling signal, especially when 1-.J--1.-h.t~I--l-lI-l--+/1 - +-I- H - I-H'..... r---r ~ - - Fig. 10-3. Air-load -- the stimulus is at a frequency at or near impedance per unit '1''\ area of cone in in­ resonance. Behavior at other frequen­ / 1- finite baffle. After cies follows the laws of resonant Olson. systems unwillingly forced into un­ natural vibration. • Speaker Dynamical Analogies Dynamical analogies relating mechani­

1000 10000 '0000 cal, acoustic and electrical phenomena FREOUENCY IN CYCLES PER SECOND prove helpful in the understanding and de­ sign of speakers. Many articles on e1ec-

32 AUDIO ENGINEERING • MARCH, 1953 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 pliance controlled. (In the analogous the fact that the air load resistance 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 powder 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. locity loops and retained by the nodes). (B), so the acoustic output of the ·speaker is Cone break-up at 2700 cps. After Corrington. At resonance only friction must be kept fairly uniform, in spite of decreas­ overcome and the velocity of the cone ing velocity of motion, up to a fre­ tro-acoustic devices have appeared which will be at a maximum. Just as inductive quency at which the air load resistance 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-tll,e 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 iI1€lrtial and restoring forces are borhood of 700 cps. Electrical Mechanical just equal. Above this point speaker output Voltage Force At frequencies above resonance the should start decreasing in inverse pro­ Current Velocity system becomes mass controlled (the portion to the frequency, but an ad­ 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 The mechanical system of a ' loud­ tive reactance decreases with fre­ vibration, (see Fig. 9-4), so that the 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 creating high compliance at predeter­ detract from the total inductance of the tion of the audible spectrum of sound combination. The two capacitors must frequencies, with peak output at the mined points along the line from base 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 fa~or 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 be taken to help achieve suffer, and peaks and dips are intro- as each capacitor reduces the total ca­ pacitance of the electrical system. An- • other way of seeing the necessity for representing the two cone suspensions with a series electrical connection is to think of one of them as frozen. Cone ve­ 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 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 loudspell.ker mechanical system of (A). when alternating magnetomotive forces of various frequencies are applied to the voice coil. The analogous electrical O~'" circuit will be referred to when it seems • advantageous. Such references are only Co for the sake of clarification; they are not essential to the explanation. For Rc Rrz 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 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 ~ SOH'" er's bid .for a life of its own are: ing and increased efficiency. Since the (SLOCKE D resistive component of the acoustic load IMPEDANCE ) 1. DAMPING. impedance allows power to be perma­ In an electrical resonant circuit the nently transferred to the medium, the i! SEEN BY VOICE COIL ' f ·t · S OHMS presence of resistance dissipates energy resistance reflected back into the speaker in heat. Instead of energy merely being cone is called 1'adiiation 1'esistance. tossed back and forth between coil and E lectrical 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 tL6!(I) .SAMP ~.,8 OHMS~" .. chapter on power amplifier stages, is I' . becomes broadly tuned and has its also very effective and does not create ] resonant peak reduced, a. condition in efficiency loss. which it is said!o be damped. r SE EN BY VOICE COIL = f = t"' 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 cases it is possible to keep speaker and the time required for oscillations 3. DISTRIBUTION OF MASS OF THE to die out, are decreased. Speakers are resonance below the main band of fre­ MOVING SYSTEM. not, of course, purely mechanical sys­ quencies being reproduced. Typical tems, and they are damped in thl'ee values for commercial speakers twelve The principle of inserting cone cor­ ways: internally, through mechanical inches and larger are from forty to rugations for controlliJ1g 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 1n 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 cOll1mercial 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 sound propagation and dispersion. At suspensions will" obviously cause a se­ tively linear restoring force so that the low frequencies the entire suspended voice coil is not carried out of the area vere loss in efficiency, since the energy mechanism vibrates as a unit, but at dissipated is entirely wasted. It is of uniform magnetic field, or does not especially advantageous, however, to allow the voice coil to "bottom" against high frequencies the small cone and damp the rim suspension of the cone tbe 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 s, the of impedance discontinuity, a good part is to say it adds mass to the speaker stiffness of the spidgr, determined by C8, of the energy that has not been radiated system and lowers the resonant fre­ the mass intertia of the voice coil Mve, can be dissipated in the mechanical re­ quency. Although we normally expect and the inertia of the first section of cone and aluminum done Mer At this point, sistance of the suspension, instead of a mass reactance to increase with being reflected back along the cone. frequency, the air load is peculiar. marked X on the diagram, there is a choice of path. At low frequencies Ce The formation of standing waves is thus Above a certain frequency (see Fig. will have a high impedance (will remain discouraged, while vibration of the cone 9-3) the reactance d'e'creases with fre­ mechanically stiff) and Me2 a low im­ in smaller masses can still take place. quency, so that compared to the mass pedance, so that current will flow through Standing waves are also dampea by the reactance of the cone and voice coil it is M efl ,rather than Ce. The current through use of a soft, spongy cone material. greatly reduced at higher frequencies. M e2 will be the same as that through Mel' Energy absorbed by the air load re­ It is a case of having our cake and which represents the fact that the two sistance 1S 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 imped­ ances 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 C e, which 50 means that half of the energy supplied will be used up in vibrating Me- inde­ • pendently from M e2 . The compliance of Ce relative to other components of the II Fig. 9-6. Electrical '"<.> system is adjusted so that the impedances ..z / voice-coil impedance of the two parallel paths become equal ~ 30 / of typical 8-ohm at the desired frequency, called the cross­ 3! spea ke r. After F. over frequency. The system of mass and / Langford Smith. compliance which determines the fre­ quency of equal path impedance is some­ g / '"o times referred to as a mechanical cross­ > !/ 10 r\.. • over network. At much higher frequencies Ce as­ sumes a very low value of impedance. Current is short circuited through it ...... '0000 " 1000 leaving little or no energy for Me : FREOUENCY IN CYCLES PER SECOND z ( Continued on pa.ge 66)

34 AUDIO ENGINEER ING • MARCH, 1953 THE MAURER, 16mm IN ROME

When Ken Richter makes a foreign­ location documen­ tary for a firm like Reed and Barton, Silversmiths ..• you THE MODEL F PRIME RECORDING OPTICAL SYSTEM AND GALVANOMETER. A complete can expect to find the Maurer light modulating unit for recording sound photographically upon standard film, reo "16" on the job. To the pub­ quires no special servicing or spare parts THE MAURER 16MII., designed specifically lic, this sequence illustrates (other than recording lamp). for professional lise. equipped with pre­ cision high.power focusing and view·finder. "The Romance of Silver De­ Standard equipment includes: 235 0 dis­ solving shutter, automatic fade control, sign." To the professional it view finder, sunshade and filter holder, one proves the better results 400·foot gear-driven film magazine, a 60· cyete lIS-volt synchronous motor, one achieved with the camera 8-frame handcrank. power cable and a designed for professional use lightweight carrying case. •.. the Maurer "16." THE 16MM. SOUND·ON·FILM RECORDING SYSTEM combines the highest fidelity in 16mm. recording practice with wide flexibility and extreme simplicity of operation. For details on this and other MAURER equipment. write: maurer

AUDIO ENGINEERING • MARCH, 1953 35 Wit• h· no Increase ••In ·nOise It's the new

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The term "SCOTCH" ·and the plaid design are registered trademarks for Sound R ecording T ape made in U.S.A. by MINNESOTA MINING & ¢:.-~, MFG. CO., St. P aul 6, Minn.-also makers of " Scotch" Brand Pressure-Sensitive T apes, "Undersea!" Rubberized Coating, "Scotchlite~' Re­ .8ective Sheeting, " Safety-Walk" ·N on-slip Surfacing, " 3M " Abrasives. "3M" Adhesives. Genera! E xport : 122 E . 42nd St., N ew York 17, N. Y. • Ib Canada: London, Ont ., Can. or harmonic distortion!

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High.()utput and ~ TM 3M Co. 1953 Radio Engineering Show GRAND CENTRAL PALACE, NEW YORK-MARCH 23-26 Year's largest exposition of electronic equipment again takes to . the boards fo r its annual four-day stay-in conjunction with IRE convention which offers literalIy hundreds of technical papers.

ARCH INVARIABL Y BRINGS fo ur days A Thursday afternoon session on Audio of sightseeing to the electroni c en­ will cover : "Sound Reinforcement System, M gineers, with its associated foot­ General Assembly, United Nati ons" by L. tiring walking past and into myriads of L. Beranek, "A Variable T ime Delay" by booths, each holding some equipment of in­ Kenneth Goff, "A Flux-Sensitive H ead for terest to everyone-some with di splays of Magnetic Recording Playback" by David exceptional interest to those in audio. A l ­ E. Wiegand, "Uniaxial Microphone" by though all branches of electroni cs are H arry F. Olson, John 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 ]. K . so the IRE show does not compare to an AUDIO H illiard. T hree sessions are devoted to A udio F air as an attraction to mos t of transistors, largely from a scienti fi c view­ JE' s readers. H owever, since there is no ENCIN!!ltlNC 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. T he Radio E ngineering Shows are not Most of the audio exhibits are concen­ open to the public at large, although there trated on the third fl oor of Grand Central is nothing to keep anyone away--except P alace, and are listed at the left of the the three-dollar admission charge, pos­ di agram below. Certain other exhibitors sibly. IRE members al·e admitted fo r 9ne having considerable audio equipment are dollar, and are also privileged to attend located elsewhere in the building, and are the technical sessions. papers : "Fundamental Theory" by L. L. listed at the right. As, usual, JE wi ll be A new feature this year, seminars are Beranek, "Microphones" by Harry F. there,· being located .this year on the third being presented which will undoubtedly Olson, "Loudspeakers" by H ugh S. fl oor in Audio Center. Also on hand wi ll be bring fo rth many interesting discussions. K nowles, "P honograph R eproducers" by the 2nd A udio Anthology, as well as the Two sessions are bein g held on "Acoustics B. B. Bauer, "T ape R eco rding" by Marvin first one, along with current issues, infor­ for the Radio E ngineer" Wednesday·morn­ Camras, and "Studio Acousti cs" by H ale mation about subscriptions, and anything ing and afternoon, with the fo..llow..ing ]. Sabine. else our readers are likely to ask. AUDIO CENTER ~ ! ~ . ._ .. AUDIO EXHIBITORS / EXHIBITORS . . ON OTHER FLOORS _ a

3·317 Altec lansin g Corp . .L1• M 'O 1 : :110. 4·405 Am pex El ectric Co. Amplifie rs, tuners, loudspeakers Tape Recorders 3·314 Ampliner Corp. of Amer ica =:£' w: 1·406 Ar nold Eng ineering Co . Amplifiers, tape recorders . _- - , Magnetic materi nls, core!) . 3·105 . Audi o DeYices, " Inc. ~ 1 ·112 Baliantin . laboratori es Audiodiscs, Audiotape, Audio- : , .:,~ .. , r~"o. ; Test Equipment points 2·128 Barker & Williamson 3·310 Audioco m, Inc. Audio test equiDment "High Fidelity" magazine :,.,,, 2 ·515 British Industries Corp. 3·304A Derlant ASSDCiates Speakers, ampJifiers, solder Concertonc tape recorders ," '1 2·106 Browning Laborator ies, Inc. 3·400 Fairchild Rec . Eqpt. Co. Radio tuners, AM, FM PhOllO pi ckups, tape and disc re- It= - ~, :) ,,~ 2·512 Cannon Electric Co. corders, and transcripti.on .. i AUDIO Plugs and connectors I turntables " o4, ." .4 : ENGINEERING 1 ·801 Collins Radio Comp any 3·304A Fisher Radio Corp. ;,.,n -:.' Radi o broadcast equIpment AmpUfiers, tuners, systems t: 1·118 Th e Daven Company 3·.309 Hyc or Comp any Attenu ators, test equipment f.-~ ~ ~ ~ I , w j !: • : ,. • j .. .,·,n Toroid coils. filt.rs. .tc. ~ & uo.o , ~ r -- __ J __ c- ., 1·109 Free d Transformer Co. · I '_I"~I . 1)0', , ~ , 3·506 Jense n Man ufacturi ng Company , Transformers, test equipment Loudspeakers ~ ~ - 1 ,, ·)r. 2·324 Gates Radio Com pany , 3·301 Mag necord . Inc. :)oro, : ~: Radio broadcast equipment l\'fagnecordel' tape recorders f~ · ~ 1·201 General El ectric Comp any 3·506 Th e Muter Comp any : ;. :~:: ~ , C,·,or: Loudspeakers, pickups r-- -, Louds peakers, compOifents f - ----~ 1·121 General Radio Company 3·306 Presto Recording Corporati on :... ,01. , Laboratory a nd test equipment ~ _ _ _ J I In.a , Tape and disc recorders and L ______1·402 Gray Manufacturing' Company playback equipment H ~ Pickup arms, transcription eCJ Pt. 3·.315 Racon El ectric Co. 1·509 Hewlelt·Packard Co. Loudspeakers, horns Test equi pment , 3·316 Radio Ma g az lne ~. In c. 1·110 I nternatlonal Resistance Co. AUDIO ENGI/I'EERL'lG. the Resistors, potentJometers, etc. ·Audio Anthologies 2·327 Measure ments Corporation 3· 506 Th e Rol a Company . ~~• , I;: ; . = Laboratory and test equipment Loudspeakers, components 1·304 Radio Corp. of Am erica 3·112 Tech · Master Prod ucts. In c. .... ~.. I , TV equipment, tubes Amplifi ers. TV sets and kits 2·210 Shall cross Mfg . Company 3·311 Uni versity Loudspeakers. Inc. Attenuators, swi tches. etc. Loudspeakers, horns 4·801 Stand ard Transformer Comp any 3·313 Waveforms, Inc. • Transformers . ampl ifi er kits Am plifiers , test equipment 2·146 Tech Laborator ies , Inc . .3 ·402 Zift · Davis Publishi ng Co . Attenllators. switches, etc. " Radio & Television News" 4 ·602 Triad Transform er Company Magazine • • • Transformers, amplifier kits 4·715 Tung ·Sol Electri C, Inc. Tuhes- 5881. 5687. etc. 1·132 United Transform er Co mpany Transform ers, amplifie r kits THIRD FLOOR

38 AUDIO ENGINEERING • MARCH, 1953 The PRESTO Re·7 has already been acclaimed " the fin est tape recorder of its size available." Although portable in size, the Re·7 embodies features and heavy duty construction found only in larger, more expensive, studio· Compare the RC·7 with any type machines. studio-type recorder Now, with the new RA·1 reel adapter, " is precision recording instl'ument • Instantaneous speed accuracy becomes an indispensable piece of equipment for every station and record· • Dynamic range better than 50 ing studio. With this adapter, the Re·7 accommodates reels up to 10%" db. at 3 % distortion diameter, providing continuous long·period recording or playback. • Three·motor drive If you are contemplating a portable tape recorder, don't buy any-until • No friction clutch or friction you see the PRESTO Re·7 with 10Ih" reel adapter (RA·l). Without a doubt, brakes it's the best buy in professional tape equipment! • Heavy duty construction throughout, • Separate erase-recording­ playback heads Present PRESTO RC-7 owners may convert their machines with • Twin speed: 7V2"/sec or this adapter for just $39.00. Write today for details! 15"/ sec. • Frequency response to 15,000 cps • • Reel size: to 1 OW' (with RA-l adapter) 00 RECORDING CORPORATION PARAMUS, NEW JERSEY 25 Warren Street, New York 7, N. Y. Walter P. Downs, ltd. Dominion Square Bldg., Montreal WORLD'S LARGEST UFACTURER OF PRECISION REC ORDING EQUIPMENT AND - DISCS "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.

PROVISION 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 A 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 welI 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 J ustice 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 di sappears; and strengthening lier applicatiQn 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 coYrts 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 inventol" 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 pat­ ent 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 25 years of leadership in sound

You (on (hoose with

(onfiden(e when it's 0 Jensen High Fidelitv Loudspeaker

o Because more people listen to Jensen than all other hi~fi brands combined -leadership achieved through proved superiority! 8 Because Jensen gives you a complete range of prices-with top performance in every price bracket - you can enjoy luxury listening no matter what your budget!

@) Because Jensen has the finest, best equipped acoustic laboratory in the business, carrying on a continuing, forward-looking research and . engineering program - you can be sure Jensen products incorporate all the latest advances! e Because Jensen is the oldest and most experienced maker of loudspeaker equipment - and the standard of quality throughout the world -you can buy Jensen products with utmost confidence!

And because Jensen is the only complete line of hi-fi loudspeaker equipment, your selection is easily, quickly, surely made.

Write for 20-page Book - " How to Choose Your High Fidelity System." Complete information on how to selec t components for your hi-fi basic phonograph system. Includes new, handy 5-step PRICE PLANNER worksheet that helps fit selections to your budget. Write for Brochure 1030 today, send 25c in coin.

Jensen Manufacturing Company 6601 South Laramie Avenue, Chicago 38, Illinois Division of The Muter Company in Canada: Copper \Vire Products, Ltd., Licensee Audio Fair-Los Angeles Rated Huge Success Record attenda nce exceeds New York Fair records by nearly 50 percent - justifying Cal ifornians' claim to great interest In audio in that loca lity.

URPASSIN G the expectations of nearly everyone in the industry-with the Spossible exception of those who were responsible for the show itself-the first Audio Fair in Los Angeles drew an attend­ ance 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 rep­ resented by approximately 75 exhibitors, the Fair offered everything from wireless microphones of broadcast quality, to three­ dimensional tape-recorded sound-the lat­ ter being remembered as the hit of the last two New York shows. The Fair Directory included a page for Left. to rig ht: ".Ca p" Kier ul ff, publ ic ity director of t he Fa ir; Boyd McKn ight, chairman of t he comments from those who heard the stere­ AdVisory Committee and for,:"er Sect ion C h a ir ~an ; a~d R i ~ha r d 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 were noted by the enthusiastic li sten­ pa ~n of advertising, press releases, and meeting were those on stereophonic re­ ers: "Very life-like--as near to the actual 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-for home enj oyment will be Cara, as well as Mr. Kierulff. Otto C. Bixler and C. G. Barker. All as­ more than worth whatever the cost may be AES Technical Sessions pects of audio engineering were covered -a little too loud for the room and the by the convention papers, which will be In addition to the exhibits, the Los An­ audience--how will it be made available published in the Journal of the Audio E n­ for the public- too loud in spots but I still geles Section of the Audio Engineering gineering Society. The first issue of the enjoyed it-TOO LOUD (but OK)." Just Society- sponsors of the Fair- staged an J olwnal 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-once they are introduced to work of the Section Chairman Richard real high-quality reproduction. Hastings, Papers Committee Chairman will be published in the late spring. The J O I~I'na l of the AES is a new activity of On the back of the sheet which provided Robert H opkin, Advisory Committee space for comments was a questionnaire Chairman Boyd McKnight, and the Chair­ the Soci ety and is headed by Lewis S. regarding where the visitor had heard of man for the Technical Sessions Allan Goodfriend, Editor, and J erry B. Minter the Audio Fair-and the surprising result Wolff. In all, 19 papers were presented in Chairman of the Publications Committee: was that the majority of them had learned the four sessions, covering Aircraft com­ Members will receive the J oumal without of it by radio, with newspapers rating a munications and recording-motor systems, extra cost, and non-members may obtain close second, and TV third. And for this Audio components and measurements, Au­ copies at a nominal charge. 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 rllsh • hours of the three-day show, the rooms and corridors are admirably suited for the demonstration of audio equipment. The William L. Cora, Fair Ma nager, 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 sh ow, pre­ the H-like arrangement of the hotel per­ pares to introduce mitted relatively free movement of the Maximil ian Weil, of visitors so that the show did not appear to Auda k, in successful be as crowded as the corridors of H otel ! bid for attendance. New Yorker in the original Audio Fair locatio'!. But taken from all its aspects, t 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 l _____ --'-' ___ .....1 standing vote of appreciation.

42 AUDIO EN GINEERI NG • MARCH , 1953 get immediate SOUND WORKSHOP'S delivery on this new CUSTOM 800 COMPLETE SYSTEM An outstanding FM-AM Radio-Phono combina­ tion that excels standard type consoles selling at deluxe equipment higher prices. Supplied complete-ready for oper­ ation. High-fidelity components include: Pilot FM­ AM AF-S21 Tuner; Webster-Chicago 3-Speed Changer; Jensen H·222 12" Coaxial Speaker; Grommes 100 BA 1 O-Watt Amplifier; G. E. Triple­ Play Variable Reluctance Cartridge. Beautifully housed in outstanding modern cabinet... with acous­ tically designed speaker enclosure. Size: 53" W, 32'12" h, lS" d. Shpg. wt" 110 Ibs. FISHER AUDIO COMPONENTS 98-641_ Cordovan Mahogany. 98-642. Blonde. Model 50-A Lab St'.:;ndard Amplifier. Deluxe 011 - Either Model, Net·...... $391 .50 triode amplifier of the utmost fidel onse: £ 0.5 db, 15-60,000 cps at 40, wat.ts. ic 'distortion: ALTEC SPEAKERS .05 % at 5 watts, .OS % at \ 0 wat at 40 watts. Intermodulation: 0.4% at 10 wai % 'at 40 watts. 820A Corner Speaker System. Altec's finest Hum: better than 92 db bela\;; full output. Output im­ speaker installation. Response exceptionally Rat from 50-16,000 CPS; 30 watts power rating; CFOSSa pedance: 8, 16 ohms. Chassis size: 8 x 14112 X 9 '/ high. over 800 CPS; output matching imp. from 6·12 Complete with tubes. For 105-125 v., 50-60 cyciesAC. ohms. System consists of: 821 mahogany corner Shpg. wt., 45 Ibs. 'i: cabinet; S02B high frequency unit with H-SOS 98-628, Net ...... multicellular horn, two S03A 15" low frequency speakers and N-SOOD dividing network. Cabinet Model 50-C Master Audia Co~trol. Ear use with ' 47%" h, 42%" w, 29" d. Shpg. wt., 230 Ibs. amplifier above or any other Qualit ~ , (Jmplifier. Inputs: 95-048. Net ...... $525.00 3-for TV tuner, radio tuner, t.ape ~ Iayback; '1-011 . magnetic cartridges; 1-high·imp. mak~e. 9u1puts: 1- 604C 15" Coaxial Speaker. Flat response from for amplifier; l-for recorder. Response: ± ·1 'db, 20- 30·20,000 cps. Has 15" cone for low Frequencies; 20,000 cps. Harmonic distortion: .05%at. 5 Y. , 0.4 % 6-cell high-frequency tweeter coaxially mounted for 60° hor., 40° vert. distribution. With N-1600A at 15 v. Intermod: 0.2 % at 5 Y. , 1.6% at 15 Y. In rna" l hogany cabinet, 15% x 4'12 x 6%" deep. With tubes. crossover network. Ratings: 50 watts peak, 35 watts continuous. Voice coil imp., 16 ohms. For 105-125 Y., 50-60 cycles AC. Shpg. "::1.79 Ibs. Depth, 11'/8". Shpg. wt., 57 Ibs. 98-626. Net ...... ' $;:.50 95-057. Net...... $156.00 602A 15" Duplex Speaker. 30-20,000 cps ELECTRO·VOICE 4·WAY SPEAKER1SlSTEM, 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 radiator design f~r truly magnificent 50~~na realism. for smooth distribution. Power rating, 20 watts. Perfectly matched components include: '{I SWK 18". Shpg. wt., 25 Ibs. L-F driver (16-200 cps): 12W-l L-F drive'! (200-600 95-084. Net ...... $114.00 cps); T,.25 treble driver (600-3500 cps) e.xnau,ting through 6-2X5 cellular horn; spa BT a" super-tweeter augmenting T-l0 HF driver to full-powered, 16,000 BROOK 12A4 AMPLIFIER cps; X-26 '<-1 4-way Crossover (200, 600. 3500 Consists of Model 12A basic ampli~er cps). Houst..l in distinguished custom corner c'gbinet. and Model 4A preamp. Response: ± All components installed and wired. 60" h, 41" W, 0 .5 db, 20-30,000 cps at 10 watts. Har­ 30" d. Shpg. wt., 500 Ibs. monic distdrtion: 1.21 % at 10 watts. 81-413. Mahogany. 81-414, Korina Blonde. 1M: 2.56 % at 10 watts. Output imp.: Net, either model...... $712_95 2, 4, S, 16, 500 ohms. Amplifoer size, 17 x 6% x SVo". Complete with tubes. Shpg. wt., 2S Ibs. 98-701. Net ...... $222.00 CRAFTSMEN 800 FM·AM TUNER Model 4A Preamp Only. Features The famous tuner with the outstanding features: new 9-position record compensator and wider AM bandwidth; sharper IF bandpass "skirts"; "ih loIJdnless control. ReQuires power supply built-in preamp with front-panel selected equaliza­ w~n used with amplifier other than tion for recordings; AFC; "magic-eye" tuning; B,foo,k 12A. Complete ,:,ith tubes. Shpg. tuned RF on AM and FM; separate triode conver­ wt., 10 Ibs. ters; output, 2 v. at less than 5 % distortion; output ,9a. :002_~ et...... $1 09.50 matches high- or low-gain amplifiers with input imp. of 10,000 ohms or higher; input for TV, recorders, _h ~ etc.; dual tone controls. Chrome-plated chassis, GARRARD RC.;80 CHANGER 13% x 1 Ov. x 7". Complete with tubes and cables. Plays all speeds (n'h, 45, 7S rpm) and all sizes (7" .10", For 105-125 v., 50-60 cycle AC. Shpg. wt., 17 Ibs. 12/) automatically. Chang~s 45 rpm re cords ~on special 98-002. Net ...... $159.50 spindle- no adapters required. Shuts off oulo~ atically af(er last record is played. With 2 plug-in heads 'and hard­ ware for G . E., Pickering or Clarkston. carfr. idge~s. Less cartridges and preamp. Shpg. wt., lS Ibs. . , FREE 1953 CATALOG 96-422_ Net ...... , _.

Write today for aur complete 236-Page RADIO CORP., Dept. 17-C-3 Buying Guide listing the world's largest 833 W. Jackson Blvd., Chicago 7, Illinois selection of High-Fidelity systems, amplifiers, tuners, speakers, changers D Send FREE 1953 ALLIED Catalog. and accessories-available for immediate Ship the following equipment: •••••..•••••• • •.•• •• .•.• •••• •.• - •• • , shipment from stock. If it's anything in Hi-Fi, you'll find it in your ALLIED Name •••••••••••••••• • • •• ••••••••.. •.. .. • • ··········· · _· · ·· • Cat,dog. Send for it today. Address • • • , _ ' " _ .••• ••••••••••• •• •••••••••• ••• ••••••••••• ••• ALLIED RADIO I City .•••.• • • •• • • • •.••••.• •. • .•..•.•. Zane ••• •• • State ••• ••• • . ••• AUDIO ENGINEERING • MARCH, 1953 43 .20 I pLb~bI I Jos1T ! oN I Equipment Report - PREAMP "IN" 0 "- 1I1 1II1 . PILOTONE AA-901 Amplifier and AF-821A PILOTUNER 0 :-N- -- 0 PHONd (~R~ ~~~ '''OU T:') HE PlLOTONE AA-901 amplifier employs 10 watts the distortion remains below 0.4 .1 0 -10 AND TV per cent. ~ the conventional Williamson circuit, /?;i-,. with a number of desirable features. The amplifier chassis is provided with a 0 '/ T ~T I I I I II I i"- // 11eans 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 - I o - - TONE CONTROL RANGE 'V between the two tubes. By connecting a l~re 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 A11-F11 tuner, tone and vol­ , I I this voltage to suit the tubes. With KT-66's ume controls, and a phono preamplifier which may be switched in or out at will, PI LOTONE I -normal equipment in the amplifier-40 I-- AA-90\ volts is recommended; if the user wishes thus making it possible to change from to change to 5881's, the correct bias is 38 crystal to magnetic pickups with a mini­ , / 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 F11 ,.....V 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 " . ~ .. .. POWER OUTPUT" - WATTS " Rated output is obtained with an input tions; the A11 pickup on the iron-cored voltage of 1.0, which corresponds to a antenna coil is sufficient for most installa­ Fig. I. Measured performance data for t he O.25-volt input for the standard measure­ tions. Pi lotone AA-901 a mplifier a nd t he AF- 821 ment output of 1 watt. 111 distortion at the While tone control curves seem to be Pilot uner. IS-watt output is 2 per cent, while up to less severe than many others, they would undoubtedly be adequate for normal instal­ 1 PH,u[IHV(II TEII lations. T he phoria preamp has a fixed equalization curve which matches LP rec­ ords quite closely, and tone controls per­ mit 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 af­ fected by the volume control, or to an am­ plifier which was equipped with tone and volume or loudness controls of its own. Two convenience outlets on the tune!' chas­ sis can be used to accommodate the power amplifi er and a turntable, and both are controlled by the on-off switch. The se­ lector switch also controls dial lights-il­ luminating the one in use- or operates pi­ lot lamps for the phono and TV positions.

Fig. 2 (left). Schematic of the Pil otone ampli­ fier. Fig . 3 (below). Schematic of the AF-821 Pilotuner.

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44 AUDIO ENGINEERING • MARCH , 1953 The ORIGINAL The NEW WILLIAMSON HR-15 MIN IFO N Amplifier Kit Miniature, Portable Th e famous, original WIRE Wi Wamson HR-15 • • • s till accl aimed th e RECO RDER leoder . .. in kit form , with th e Partridge Out­ Measuring only 17'8 x 4% x 6%, and weighing only 2 Ibs_ put Transfo rmer spe cified by Williamson in his ori ginal design . Assemble this kit, and in 3 hours or less, enjoy the finest sound you ever heard. 7 azs_, th e Mrnifan is just about the world' s smallest sound Ope rate s from a tuner, phono-preamp, crys tal pick- up, or othe r sig nal recording in strument_ Records, rewinds, erases, and ploys bock source . Absolute gain is 70.8 db with 20 db of feedback. Freque nc y through either a pair of stethoscope type earphones or on r esponse: - .5 db, from 10 to 100,000 cps, Output impedances to match all spe ake rs from 1.7 to 109 ohms. Kit is complete with 5 tube s: 1.5V4, external amplifie r_ Capacity 2Y2 hours uninterrupted recording_ 2-6SN7, and 2-588 1 lor 807 i f requestedl, 2-Punched Cha ss is, 2-R es istor Powered by 1 '12 v_ A battery, standard 30 v_ B baltery, and 7 Mounti~g Strips, Sockets, Partridge WWfB Output Transforme r, As sembly Mallory RM-4Z me rcury batteries_ An ideal tool for executives, In structtons, and All Other Necess ary Parts for Ampli fi e r and Power Supp ly .... _ ...... _...... _.. _._...... $76_50 e ngineers, doctors, and wh e rever th ere is need for recording notes, interviews, and othe r data. PARTRIDGE OUTPUT TRANSFORMER WWFB - Available Se parately __ ...... $26.50 Comple te with microphone, ste thoscope type earphones, $289 50 1 hour spool of w ire, tubes, batteri es, end instructions. • HR-I5T Williamson Kit - Furnished as above, with TRIAD Morocco leather Zipper Case ...... $10.00 Transformers and Chokes ._...... $69.50 Transformer-rectifie r Unit for ope ration of motor from NOTE: HR-15 and HR-15T Kits may be had with 117 y _ AC line ...... ,...... _...... $20.00 British KT-66 Output tubes for $3 _00 additional _ RECORDING WIRE On spools, in dust-proof plastic containers, suitable for moiling. The NEW V. hour ...... $5_00 1 hour ...... $ 9 _00 ';' hour . 7_00 2 hour ...... 17.90 MciNTOSH 2 11:1 hour . 21.50 LOUDSPEAKER SYSTEM AUDAX POLYPHASE . REPRODUCERS Housed in an attractive enclosure for either flat-wall or corner .Iocation_ Provides a response ± 3 db_ from 40 to 10,000 One unit with two replaceable styli operating cycles/sec., and a useful response from 30 to 20,000 cycles/sec. with one pressure (8 Y2 grams) for aU three record Four 12" speakers are used for low frequencies, on 8" speaker speeds: 33 Y3, 45, and 78 rpm_ Provides exceUent for th e mid range and four tweeters for high frequencie s_ coupli ng betwe e n stylus and record groove, with Nearly 4 square feet of diaphragm area are thus provided high stylus compliance a nd minimum mass_ Re sponse is from 20 to for more efficient acoustical coupling, more closely approaching over 10,000 cps_, with an output of about 20 miUivolts_ Needle-talk linearity in excursions, thereby reducing low frequency distor­ practicaUy ni l. tion to a minimum_ Over-all width of the enclosure is 43 inches, and the height is 30 inches_ Front width is 22 Y2 inches_ Power DL-6 Chromatic Head with Microgroove Rating : 50 watts continuous operation. Impedance: 8 ohms. Diamond and Standard Sapphire._ .. __ ... _. _ $47.70 Model FlOO (blond finish} _____ .. ______.... _.. ______.. ._ _.. $374.50 L-6 Head with two Sapphire StyI L ...... _.... _.. _. 20.70 KL-4 Head with Sapphire Styli ...... _.. _...... _. __.. .. . 20.70 Model FlOOA (Mahogany finish} .... __ .______.. .. ____ .__ _ 374.50 (for record changers)

CARTER SUPER CONVERTORS SPEAKER De liver clean 60 cycle AC power at 115 vo lts. Operate from storage batte ri es or othe r DC • ENCLOSURES source, and a vailable for 6, .12 , 24, 28, 32, R J 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, thi s new sensation in high fidelity has no co ~ nterpart in anything CANNON PLUGS and CONNECTORS available today. The R-J is a new 'con­ The standard of qual ify for over 15 years. You'll cept_ Lorge enough only to accommodate find the m w herever the ultimate is required in low the speaker, it reproduces tones to the lowest limits of audibility, level sound transmission, and ge neral electrical and cleanly and without hangover_ The R-J is the amazing solution e lectron ic ~c applicati o ns . Write for comple te data and pri ces. to the problem of space versus quality_ Model FM (Mahogany) ...... , ...... $49.95 COMPLETE STOCKS CARRIED AT All TIMES FOR IMMEDIATE DELIVERY Madel FB (Blonde)...... 54.50 Madel F15UM (Unfin ish ed Mahogany) 15" only ...... 43.35 S.pecify for 12 or 15 inch speaker.

Whatever it is in the fie ld of Audio , you can b e sure to find it at Harvey ... in stock, and ready for immedl· ate de live ry whereve r you may be. Your inquiries are invited . NOTE : Prices Net, F_O.B_, N.V_C. Subject !o change without notice,

AUDIO ENGINEERING • MARCH, 1953 45 HE COLUMBIA 360 hi-fi phonograph, pic­ Filling the Great Gap firm, by chance, should have some oth~r tured on the January cover of JE and special interest in the phonograph- say 111 Tdescribed in this issue, page 28, is not records-then so much the better. There going to replace your present hi-fi system. aren't many large outfits that fill this rea­ in this magazine may have shown you, is It's not supposed to. Its speaker facilities sonable description. Only one has showed well launched by now. The cycle is almost up so far-CBS-Columbia. will not compare with your Lansings ,and complete. Altecs and J ensens and Klipsches, your Come to think of it now, it was inevitable A lmost-but for one very large and that CBS should come to this. CBS EV, Brociner, Bozak, University, Wharfe­ complex factor, the sales systems. The final launched the LP, then found itself selling dale, Hartley, Barker (whew ... I'm dealers in phono equipment are now, as LP players; the CBS-designed cartridge in only trying to be impartial. .. . ) systems, above-mentioned, ranged in two camps, them matched the LP record's quality nor should it. The amplifier is probably championing the list and the net. Perhaps pretty well-but the home radios and pho­ not 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 were obviously of the bottle-neck sort. The new ceramic cartridge is unlikely to entire systems behind 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 (thoug)1 it's not far behind them in sound shops. Not unless it is priced about the signing a complete improved system for quality). The changer is just a good same as elsewhere (i.e. in wholesale houses, the mass phonograph trade. This, then, is sound salons, etc.)-at net. We've gone changer, more or less like many another. the first really planned attempt to break too far to have two prices for the public at across the big barrier, between hi-fi and I've had one of these machines 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 been this column's concern ever since it Nevertheless, there hasn't been anythi~g isn't figured to allow the local dealer his like this before. This machine is a phono­ began and so this disquisition was also in­ relatively 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 point. Look at this as a home phono and chine in terms of sound and that of the Basic Redesigning 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 eq uipment 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 In st~ad, 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 . .. ~tandard phonograph, in simpli city, 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 (JE 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 ~eeded, 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 T he 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 unprej udiced 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 the

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

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 gl-eatest impOl-tance. AUDAX is en· 2 gineered for easy l-eplaceabiIity of the stylus-at home. Of further importance is the fact that each AUDAX CHROMATIC stylus is replaceable inde­ PULL pendently of the other.

* The magnetic attraction between pick-up and steel tm-ntable, known as the "HIDDEN-PULL", has always been a problem. When point-pressure was 100 01- more grams an additional "HIDDEN­ 3 PULL"* of 10 or 15 grams was of no consequence. Today, howevCl-, with point-pressure below 10 gl-ams, the "HIDDEN-PULL" becomes a very seri­ ous 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

A vailable with the new Compass-Pivoted Audax arms and to fit the high quality record changers

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

AUDAK COMPANY 500 Fifth Avenue New York 36 Creators 0/ Fine Audio-Electronic apparatus lor over 25 years 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. T he unit is made by Sonotone--another new entry in the fi eld-and I'm told will be available separately. If S0, it should make a good "froht end" fo r rep lacement and other use. I haven't made direct comparisons but I'd say it equals or sUI'passes the CAC crystal, the fo rmer Columbia work-horse. I t is far sim pler than the twin CAC-D and should easil y outmode it. The 360 ampli fie r shows up in the final sound. Suffice it to say that a lot of imagi­ na tion was needed to design a push-pull ampli fie r in to an ordinary phonogr'lph, where in a mill ion earlier models a single­ ended horror was considered qui te sl1 ffi· cient! Don't lose our perspective on this. How to get low bass from a small box? A fa mili ar probl em these days. T he en tire inside space here, with lid down, is a closea chamber for two six-inch speaker s, 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 speakers, I gather, a re alike except that the cone resonances are purposely slightl)' Distinguish~d for m=-~ um performance af the low~:t~price . pos- ' different, for smoother over-all response. sible for a luxurious High-Fidelity Tuner. Engineered with the pre­ Sidewise Music cision that has ch~rdcterized all of lh~ _ world-famous Pilot· ele~­ I find that the sidewise distribution of the tronic~ instrument~, over a period 6f 33 years. This magnificent new - sound via the two speakers, aiming away L... PILOTUNER incorporates many superb features hitherto. unheard·-of. from each other, is the bes t and most dra­ . in its moderate price class. Write - no,W - for. a.:full .description of matic aspect of this machine's sound. Look straight at the machine and the music this outstanding Model .#723 PILOTUNER ·... S~J/jng price, $7.9.95 " comes not directly from it but instead seems to be "in the room," without a -·PI·LOT 'RAD10 sharply defi ned source. Couldn't be better. CORPOR~'ION (Of course the machine's position in the 37-06 36th Street· Long Island Cityr. New York . listening room is a large factor. A ne.rby corner or cl ose-to side wall will do more drastic refl ecting. The machine sounds best when there is a good distance to right and left of it, with good refl ecting surfaces where the sound fin ally hits.) Further indications of good thinking are No.w. ~~ Ifu- immeJiate d./upmeH.t in the controls. On-off is at the changer. T he 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 muflled sofa cushion effect, the tone knob r.cre al­ lows 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 mat:h rec­ ords and to compensate for room condi­ a perfect companion to the most authoritative • Preamplifiers tions. Why no more ? With low di stcrtion book you now have on the subject of home • Tone Controls (and good records) there is no need fo r 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 m en ~a l inertia. It was an intelligent idea to omit ticles which have most interested IE's readers • Speaker Enclosures it, and in tell igent, too, to put the on-off during the past two and a half years. • Tape Recorder Amplifiers switch elsewhere than on tone or vo lume Customary discounts to distributors. knobs where it invites w rong settings. W hat else? A standard (V-M) shanger. Board Cover $3.00 Paper Cover .$2_00 adequate and convenient; the same light arm as in the Columbia L P changer. Neu­ ------CUT OUT- MAIL TODAY------· tral components. A surprisingly good look­ Book Division, ing heavil y bui lt cabinet, bowed out in front. And that's the ordinary phonograph Radio Magazines, Inc., that may start the great gap a'filling. P. O. Box 629, Mineola, N. Y. P.S. It sells strictly through regul ar record-radio-pl)ono dealers, right square in Sirs : Enclosed is my 0 check 0 money order fo r ...... copi es of the the middle of the standard brands. It'll 2nd Audio Anthology. soon have competitors, I'll wager. (Please check one ) 0 Board Cover o Paper Cover CURIOSITY SHOP o Old Curiosity Shop. Helen Morgan, Name (print carefully ) ...... Sophie Tucker, Wi ll Rogers, Gl oria Swan­ son, Fannie Brice, etc. etc. ) Address ...... RCA Victor LCT 1112 A wonderful m emory teaser-reissues of a batch of very famous hits and familiar voices, ranging City ...... Zone .. . .. State from the indomitable J ohn Barrymore (Hamlet) to the indomitable Sophie Tucker, Helen Kane

48 AUDIO ENGINEERING • MARCH, 1953 the Boop girl, ''''ill Rogers, Casey at the Bat thumping and banging, as though a large part ... nuff said! ExceIlent technical restorations. Key of the stage props had collapsed I (The wooden Some date well I back into the acoustical period; platform used throughout was of a fabulous reso­ most are early-to-middle electt-ica i. Outstanding record of its type nance.) t AES playback curve specified on Musically, folklorists will find this a thorough '" Folk Songs of Hungary (Bartok-Kodaly ), record hodge-podge of material- some is " authentic," vol. 2_ Leslie Chabay, tenor ; Tibor Kozma, NARTB (NAB) curve specified on untutored, primitive, much m ore is relatively pol­ tt ished and a g reat deal is about as fo lk songy as a pf. Bartok ' BRS 914 record Radio City arrangement of My O ld Kentucky Vigorous, masculine st uff, su perbly recorded Big bass; European-type low (300) Home. Or Schubert's setting of the 23 rd Psalm, and full of excitement in Hungarian Chabay's turnover; adjust accordingly which is one of the loveliest items in the set 1 lusty singing. Anyone who has fallen for gypsy Di stortion Assorted popular bands, choral arrangements by dd Elgar, Holst, and the like, round out the show. or Hungarian rhythms as in the conventional Distortion in loud passages only Extra treble preemphasis - use In short, this is no document of the folk music semi·pops and the familiar Hungarian Rha~s o die s art, nor of any other kind of music, but it was et al will relish the genuine original here, set more ro ll -off a good show to be at, and it's fun t o listen to. to brilliant modern accompaniments by Bartok Flatter-than-average high e nd­ and Kodaly. Folklore people will be interested in use less ro ll-off '.- Ibert: Concertino da camera for saxo­ the piano settings-Bartok and Kodaly have not Injection moulejed plastic, quite thin been equalled yet in t h is expert use of the modern phone and chamber orch. Gla:z:ounov: Con­ dissonant idiom t o set off fo lk music without in Intimate, close-to recording in good certo for saxophone and orch. Vincent any way distorting the musical sense of the li veness Abato; instrs. condo by Schulman, Picker­ original. \Vould-be folk-style com posers should Bi g, li ve acoustics ing. t Philharmonia PH 103 study. From older 78 discs The sax was invented long before jazz. Here's Unresonant, dead ish acollstics an item from some time back that I didn't get to * Prokofieff: Peter and the Wolf. Arthur Voice is close-up, loud review that shouldn't be tnissed. The Ibert, from Godfrey; Andre Kostelanetz & Hi s arch. Voice is at distance, blends into 1935 and with a nice feel of the 19205 in it, is Columbia ML 4625 (Vz) musical background short and amusingly skittish_ The Glazounov is x lushly romantic. The reCorded sound is unusuall y . Don't sni ff too soon I Godfrey is Godfrey and Thin bass, high turnover point (600-800); needs bass boost fine, doing the maximum for the small group of you'll recognize him here all right- but his usual in st ruments. 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 t his recording, w ithout too but our friend of the well-known pickup, N or­ m uch s lapstick, a fairly close adherence to the to middling sam ples of music and dance, a few man P. He's a musician, in case you didn't know, standard spiel t hat goes with the music. Won't com plete, most of them excerpts, faded in and out, a top-rate horn player (I h ear from good critical do your extra-bright child a bit of harm. A nd with running comment "off -~ tage" (tape-edited sources ) a s well as a conductor, as here. the Kostelanetz music is unexpectedly warm and in) . There are some stunnin g things here and t he fresh. Part of that is due to the superb record­ recording is technica ll y 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-I.lps-prob­ Se nghor & Co. t Esoteric ES 513 sonal feel for this music that he doesn't for m any ably beyond the operators' control most of the another war-horse put out by his Orchestra. time--are o ften cock-eyed. Doesn't m atter partic­ Super-hi-fi sounds of the Bush (or do I mean ularly; but more important is that the material the Veldt?), recorded Han location"-in Paris, !nternational Folk Music Festival (Eistedd­ is not well adapted to this kind of technique. Too via a nite club hot spot! It m a y be a travelling fod). Auspices UNESCO: Jack Bornoff, many items al'e too long and must be faded in and troupe, but the stuff is prett y authentic sounding, narr. tt Westminster WAL 209 out. Much, clearly, was for the <: ye. It is a bit t1 0tably the rasping voices. Not a trace of " t rain­ exasperating to hear .. . "and now, here a re ing" here! T his is a kind of h a lfbreed music, not On-the-spot job by BBC of the internationa l the famous Vlhoosis Dancers from I reland w ho too far removed from Calypso though more primi­ version of the ancient W elsh foil< festival. Short have won cout1tless prizes"- fo ll owed by a vast t ive (and fa r more cpmplex). N ative dialect,

e lor complete speci fications._

PILOTONE Amplifier Model AA-901 PILOTONE Amplifier Model AA·902 Designed for high fidelity audio . A compact, medium price, high reproduction from phonograph, fidelity unit for use where cabinet AM or FM radio, tele vision or . or other mounting space is limited. microphone input . . Full Williamson Can be operated with PILOTUNER circuit. A supreme amplifier with model AF-821 and similar tuners traditional Pilot quolity, exacting for FM-AM radio, television or pho­ Pilot specifications ... the last nograph reproduction. $46.95 word for the discriminating music lover ond hi-Ii enthusiast, - priced at ____ .. __ __ . __ $99.50 * Write for complete speci fications or phone STillwell 4-5455 * Wrj'e lor complete speci fi cations Write for circular AE-2, describing these fine instruments in complete detail. PILOT RADIO COR-POR A T ION, 37-06 36 t h St., Long Isla ncl City, New York AUDIO ENGINEERING • MARCH, 1953 49 much shouting, drums, etc., but in between" the catchy refrains are sung in thirds, not unlike j\1:exican and Latin American mUiic. A good hi·fi stunt record to have around.

"EI Pili" Flamenco. EI Pi li; Mario Escudero and Alberto Velez, guitars. t Esoteric ES 2001 (10") Another in the same series-Jerry Newman, who started Esoteric as an off-shoot to his New York record shop, sold the shOll and bought him onOCRHfT an Ampex-and-Telefunken. Be's travelling. These are evidently famous names, but m y ear detects a bit of international sophistication and show biz in the music. (They are also parts of travelling troupes.) Some too·slick harnlon ies, etc. Only a trace; the rest is fine and recording is e.xcellent, if a bit close-to.

" Mr. President" -from FDR to Eisen­ hower. 1933- 1953. Edited and narrated by James Fleming. RCA Victor LM 1753 The patch-it-together documentary history, combining commentary with the actual voices and SINCLE CASE sounds of the past, is now a familiar and ine­ sistable medium. Columbia has been at it on LP for some time; this is RCA's follow up. In many Portable ways this is a step forward. There is much new material here, little that is already fami liar; a ll Magnetic sorts of people pop up--Woolcott ("the Town Crier"), Sinclair Lewis, Huey Long, Ickes , Tape Recorder Landon. The commentar y is less editorial sound­ in g (and less paternal in tone) than the cn s work, the excerpts more v aried. Recorded voices $485 net s ucceed each other without intervening com· mentary, often answering each other, presenting AVAILABLE IMMEDIATELY different sides of arguments . 1\1any voices speak only a few words, but they are usually very well Th is professional unit consists of the chosen. The familiar New Deal years, build-up standard PT6-AH recording mechanism to war are covered with new material, the war plus li ghtweight amplifier. Amplifier has t wo inputs-one mi crophone, 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 You ' ll find all Magnecord equip ­ ing-an e..xcellent accounting. How time flies! monitor jack. Frequency-response ± 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. (Fleming's voice is occasionally hurried or tired, recorder mechanism back to back when closed. Unit is Trained engineers will give you joined by slid.:! hinges, and amplifier may be detached and between good stretches). The counterplay of operated beside mechanical unit. Weight 45 Ibs. dimen- expert advice and immediate serv· voices is som etimes confusing; you lose track of sions 19" x 73,4" x 17 %". . 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 NB C just has good recordings.)

':' 0 Dvorak: Serenade, op. 44. London Ba­ roque Ensemble, Haas. Decca DL 7533 A nove.1ty item by a familiar composer, a sere· nade 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 bassoons, contra· bassoon, 3 h orns. With that po· tent armament Dvorak produces some fine vil­ lage-band stuff with a solid tone quality that is beautifully recorded as well as nicely played. PORTABLE BATTE,RY fjd 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 seem s to work out well. Voice is somewhat tubby in quality, very slightly dis­ torted. 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? built into a handsome briefcase . . . completely battery operated! Wet cell battery for 1 Vz hours operation, re­ o Gluck: Flute Concerto in G. Carelli: Oboe chargeable from car or charger. Dry Concerto. Paris Philharm. Orch., Leibowitz. cell "8" battery good for 50 hours. Microphone with stop and start switch. Haydn: Toy Symphony. Orch. Radio­ I mmediate playback through phones Symph., Leibowitz. OCS 29 Speed 7Vz"/sec. and 3%"/sec.; wei~ ht 12'l's Ibs.; dimensions 55/s" x 13 V4 ' x Two pleasing concerto items- a concerto from 12V4". Gluck is a decided novelty since we n ormally hear only h is operatic music. and the Carelli con· certo has in it a famous sarabande that you'll recognize from popular transcriptions. The Haydn Toy Symphony is for once done without putting those d - - - wlltery bird whistles and rattles 3 inches from the nearest mike, and it sounds a lot better, remains as good fun as ever. Playing has that hard, chromium quality that Leibowitz likes so much (and I don't). Nice hi-fi, and the crow call (?) is out of this world. 50 AUDIO ENGINEERING • MARCH, 1953 ~, Menctti: Amahl and the Night Visitors. Original cast of the NBC telecast (with IN THOSE EXTRAORDINARY APPLICATIONS Chet Allen). RCA Victor LM 1701 WHERE DEPENDABILITY AND PRECISION COUNT If ever a modern classic was tossed off for eternit y, this is it. Menotti h as a peculiar genius for cutting across styles and tast es t o appeal t o almost any a nd everyone-his drama s imilarly seems to "work" in any m odern medium, wh ere other modern COluposers flounder abysm ally with you'll find the technical difficulties. A ll of that s h ows hCl-e II superbly; the pomp and circumstance of NB C [ ~ super-TV can't touch the simplicit y and direct­ W1A ness of this music and story I Records bring it ~ ~ ~ through as m ovingly as TV or st age, or what· have-you. And this music, done in a h urry by }\!I enotti, seem s to hit the essentia l spot that earlier and more pretentious undertakings-the Consul, for instance-missed for most of us. I can guarant ee enjoyment to absolutely anyone here. T he recording, too, is s uperb. If RCA h ad chosen to do this sort of job throughout its mod· ern catalogue, what hi-fi rich es we'd possess. Ter­ r ific.

':' Zwei Hen:en im % 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 li ght opera, dat ing from the incom­ fine aid to sur~ery is a joint development parable J ohann Strauss, dies hard. The Beggar of t e UniverSI ty of Pennsylvania Student (Milloecker ) dates from 1882, the fa· Hospital a nd Pennsylvania S tate miliar Zwei Herzen from 1934, and the style is College. The precise and depend­ t he same old melange of waltzes a nd nice, juicy, a ble instrument is manufactured sentimental polkas. But an inq uiring ear will find -by Centre Electronic & Mfg. Co. the Milloecker of 1882 considerably b etter s tuff, qnCAGO Sea l e d-in-~teel 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 th" song itself. dependable p erformance Superb and natural recording, the words par­ required of the instrument. t icularly clear, the voices undistorted.

CHORUS, ORCHESTRA, SOLOISTS "'dd Mendelssohn: Walpurgisnacht, op. 60. Netherlands Philh. Choir & Orch., soloists, Ackermann. Mendelssohn: d Five Songs. Uta Graf, sop. Concert Hall CHS 1159 The list of major works that have rarely been heard until LP brings them back still isn't co m plet~_ Here is some of the very best Men­ delssohn there is, a short oratorio or cantata based on the Goethe romantic t ale of the night of devils and witches. This mus ic is dralnatic, like Elijah, but simple, intense, un-stuffy, like the M idsummer Night's Dream_ Beautifully sung, in a well balanced recording. The five piano son gs are lightly and expressively sung by a lovely high The S . S. United States- last word in soprano voice, Uta Graf, with good piano ac­ Superliners- incorporates every known sea­ companiment. Somewhat distorted. Chorus dis- . going safety device. Among its electronic torts a bit in loud parts. sa fe ty features is the Announcing System Amplifier, designed and built by Electronic ':'dd Beethoven: Ruins of Athens, op. 113. Engineering Company, Inc., of Norfolk, & Va. The power transformer specified Neth. Philh. Choir Orch., soloists, Goehr. and used in this super-dependa ble c.oncert Hall CHS 1158 a mplifier is by CHICAGO. Where A companion Concert HaIl restoration, again dependability is an absolute beautifully done and of considerable interest­ requirement, you'll find this is on e of th ose work s of which we h ear 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 T urkish March. This one, t oo, distorts in the louder parts. Too high a level a t the tape reo corder input stage, I'll b et. (Remember that the naturally complex " beats," quick transients in vocal music, don't register properly on a damped meter.) Free "New Equipment" Catalog dd Prokofieff: On Cuard for Peace, op. 124 You'll want the full details an CHICAGO'S New Equipment line. (1950). Combined Choirs, State Orch. of covering the complete range of "Sealed-in-Steel" transformers for U.S.S.R ., soloists, Samonsoud. every modern circuit application. Write for your Free copy of Vanguard VRS 6003 Catalog CT~153 today, or get it from your electronic parts di5tributor. If you can bear to associate yourself with Stalin & Co., long range, you'll find our o ld friend Prokofieff, he of "Peter and the Wolf," "Alexander Nevsky," the C lassical Symphony, in excellent form h ere. Politics haven't spoiled this man, b¥ a long shot. There's a lot of bombast and a good deal of padding, to please the politi· cos, but in between, you'll find some of. the most poignantly m oving music you'll hea r In a long time and some incredibly fine singing. The can· tralto soloist has a voice you'll hardly believe, AUDIO ENGINEERING • MARCH, 1953 51 combining tenor, alto and soprano in one vast and beautifu lly controll ed instrument of un­ heard.of power ; the contrasting boy alto solo and the children's choir, contrasting with the adult choir are other elem en ts in an unfOt-ge ttablc kind o f listening. ' '''hat a language t hat Russian is, for singing! Yep, Prokofieff has h is cake and eats it; he writes what t he commissars ask for and m anages to m ake it good music as well. The recent fiRe· forestation" oratorio of Shostakovitch (VRS 422), an outwardly sim ilar big piece,. is by com· parison a servile toadying to the policy makers. Loud parts blast badly. Same story, probably.

• FREE! - 68 page catalog section from REISSUES Radio's Master. Note : The reissue of notable 78 recordings on • Catalogs the products of 30 manufac­ LP . h as been greatly stepped up ; eco11omies­ thank Heaven-now favor this procedure and turers of R ecording, Phono Equipment the sets that once were semi· white elephants and Accessories. (anyway, th ey cost a lot and weighed more) now reappear trimmed to LP (and 45) conven­ • Complete descriptions, specifications and ience. \¥ e are now getting into t he big·set area, illustrations of such products as: Record­ those huge tomes that, most of us thought, were gone for good e..xcept as coll ector's items_ B est ers, Phono Motors, Turntables, Record news of all for a lot of .£ readers: Changers, Cartridges, Pickups, Discs, Tape, Needles, etc. Db The Mikado. D'Oyly Carte Opera Co. RCA Vic:tor LCT 6009 (2 ) obd H.M.S. Pinafore; Trial by Jury. D'Oyly Carte. RCA Victor LCT 6003 (2 ) A t long last, the ancient and honourable G & S albums, beloved by generations, are up for re­ issue I About tim e. Most Savoyards agree that these are better performances t han the new hi-fi ones of recent date by the same troupe. Technically the operas ran k upward from Trial by Jury, which is tubby and somewhat d istorted at best, through P inafore, similar but decidedly better, to the best of t he three, Mikado- clear as a bell and surprisingly bright. A ll are intel­ ligible and enjoyable. Better use 300-cps turn­ over; the bass is pretty heavy.

':'0 Gounod: Faust (Highlights). Royal Ph il­ harmonic, Beecham ; Fre nch soloists and Represe nted in RADIO 'S MASTER 68 page Recording & Phon o Equip me nt chorus. RCA Victor LCT 11 00 Book let are th e products of the foll ow­ Among a whole group of opera reissues this ing manufactu re rs: stands o ut as extraordinary. Throw out a ll your All iance Manufacturi ng Co . ot.her Fausts and try the real French style! If Am eric an Microph one Co. · Ampex El ectr:c Corp . you haven't discovered the wonders of the French • "Ampli fier Corp. of Am er ica vocal sty le, which m akes the voice a musical in· OfIk.iol Th e Astatic Corp . strument as accurate as an oboe or a violin, the Guide . Audak Company astonishing Geori-Boue, also heard in Urania's Audio Devi ces, Inc. new 'Thais (Massenet), try her and marvel. Faust " Bell Sound Systems, In c. with this treatment (and old S ir Thomas knows !Ut1I11~lt 8erlant Assoc iates enough to get his singers straight from France) Inl1\llQlt Bogen Co. , Inc. Cl ark stan Corp . is believable, beautiful ; in many U_S. perform­ .. ances it is dismal1y corny _ Too bad the entire re­ Du oton e Corp. IIJiIij El ectro- Voi ce, Inc. cording is not released. It ranks very nearly hi·fi, 11l<1!lllll Fairchild Recordin g Equipm ent Co. with fine edge and sibilants. Garrard Sales Corp. General El ectric Com pany General Industries Co. Oyvv Strauss: Der RosElnkavalier (abridged ) . Jense n Industries, Inc. Lotte Lehman, Elizabeth Schumann, etc. Magn ec ord , Inc. Masco El ectron ic Sales Vienna Phil., Heger. M. A. Mill er Mfg. Co. RCA Victor LCT 6005 (2 ) Minn esota Mining & Mfg. Co. Newcomb Audio Prod ucts Co. A famous early recording by the now-retired Orradio 1ndu stries, Inc. first lady of song, a long with h er famous col­ You can obtain without cost or obligation, a complete • PentroR Corp. league, Sch umann. This one is technicall y 60· 50, Permo, Inc. fo r t wo reasons: 1) the highs are dismally lack­ 68 page catalog section as reprinted from the Indus­ Pickering & Co., In c. try's Official 1100 page Radio's Master, 16th edition. ing-probably had to be fi ltered in the copying­ Presto Recording Corp. the sound is muffled ; and 2) the o ld technique of Recordisc Corp. recording voices at stage d istance was used ; the This section catalogs in detail the products of the lead­ RecotoR Corp. Reeves Soundcraft Corp. singers aloe mere threads of tone a t times, lost ing Recording and Phono Equipment manufacturers Rek -O -Kut Compan y in the orchestral sound. For those who love Leh· - all in 1 handy booklet. I t is complete with descrip­ Shure Bros.. In c. mann- and S t rauss-the music will get through_ tions, specifications, and illustrations as written by V-M Corporation Walco Products, In c. each manufacturer. Whether you buy, sell, or specify Webster- Chicago Corp. ORCHESTRAL SERIES these products, you will find this booklet extremely Webster Electric Co. helpful. · These manu rnctul'Crs not included .Ix Strauss: Dance of the Seven Veils (Sa­ in Radio's Mastcl' scction. Separate lome): Rosenkavalier Walt:z:es. This olIer is M A IL TOD AY ('utulog sheets will accompany cach Decca DI.. 4032 (10") book!cL. made possible elx Tc-haikowsky:. Walt%, Polonaise (Eu­ by a special ar­ gene One-gin) ; Andante Cantabile. rangement be­ AUDIO ENGINEERING ,_, Decca DL 4033 ( 10") All the above with N.Y. Stadium Con­ tween AUDIO P. O. BOX 629, M INEOLA, N. Y. E N GI N EER­ certs Symphony" Smallens. Please send me, without cost or obligation, the 68 page Recording ING and the The popular lO-inch LP's are issued too fast publis h e r s of & Phono Equipment and Accessories Booklet reprinted from fOt- any hum an reviewer to keep up with! Not in RADIO' S Radio's M aster. ones but ill series. Best thing is to look at a MASTER. Be group of a kind- since nowadays a r ecording sure to get your Name session usually gets down a whole slew of works with a g iven musical combination and eng ineer­ copy now. Fill Address ...... , ...... , ing set·up. in t he coupon The Stadium Orchestra is the N.Y. Philhar­ below and mail. City ...... Zone ...... State monic in contractual disguise. T h is sel-ies feattlres 52 AUDIO ENGINEERING • MARCH, 1953 high-quality recording, distant-mike technique, in a big, resonant Iiveness. A bit too distant, con­ fuse.d. Decca's recorded curve has sharp highs, a 11Igh (800?) turnover; adjust accordingly. ex Mo%art Overtures, vol. (Cosi fan tutte, Don Giovanni, Magic Flute, Cle­ men%a 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; t hey are all played impeccably, but too fast, and exactly alike, as though they were no more than so many brilliant curtain-ra isers. One can carry this Inania for overtures too far! Mo%art: Magic Flute, Don Giovanni Over­ tures. London Symphony, Krips. London LD 9001 (10") t, J. Strauss: Vienna Blood; Wine, Women and Song. London Symphony, Krips. London LD 9013 (10") London might seem to g ive half·value- only two overtures instead of- four per ten-inch disc ; but this is a much w iser procedure. H ere there is room for expansion, proper interpretation, and the engineers, too, aren't confined. Kl'ips g ives his overtures their fu ll dignity, but the p laying is a bit lack· lustre, lacking the intensity that should be here. But his Strauss \Valtzes (see a lso Blue Danube and Emperor, DL, 901 5) are superb-sweet, ethereal, yet solid too, without the usual exaggerations of tempi, the half·bored h ack· ing·away at the old familiar tunes. London's black· label technical work is as good as any Ifrr. Price is determined by volume sales, evidently. " Beethoven : Prometheus, Fidelio Over­ t ures. Egmont, Coriolan Overture. Leonore # 3, Consecration of the House Overtures. London Philharmonic, van Beinum. London LD 9024, 21 , 22 (1 0") Six major Beethoven overtures, well spaced out for unhurried playing. Somehow, van For those interested solely in the finest possible repro­ Beillum's performance 111i sses 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 m elodies are unphrased, don't fl ow, the continuity is not good, the string beyond compare. The beautiful chairside control unit playing is weak. F ine 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 ~d a switch for the a llow it now. Fine t echnical 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 ':'iie Mo%art: Symphony # 36 ("Linz"); German Dances, K. 600. Winterthur Sym­ tion and is completely controlled from the chairside phony, Goehr. unit. The famous Altec "duplex" completes the sys­ Mus. Masterworks MMS 1 (10") "'iJe Mendelssohn: Symphony #4 ("Ital­ tem. These "duplex" speakers are the finest in the ian"). Winterthur Symphony, Dahi nden. world and are ' guaranteed to reproduce all of the Mus. Masterworks MMS 3 (10") '>\ie Haydn: Symphony # 96 ("Miracle"). tones from 30 to 22,000 cycles when mounted in the 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 lnus-ic style, very musical, soft-textured. Three splendid symphonies done in this manner, plus two Mozart dances and an unheard·of Haydn overture. 1. " Dupl ex " loudspeaker 2. 606 corner cabinet ", Mo%art: Symphonies #1, #2, #5, #6. Symphonies #4, #10, # 11 , # 14. Win­ 3. A·433A control unit terthur Symphony, Ackerm ann, 4. A·33 3A amplifier Concert Hall CHS 1165, 66 '-, Mo%art: Piano Concert #1, .# 2, #3 (After J. C. Bach). Winterthur Symphony, Ackerman. Concert Hall CHS 1164 4. If you ever wondered about the early Mozart works in these categories-here''s your music, in another fine series p layed as in the Masterworks records, above. These are · youthful Mozart, the 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 Altec "home music system" at your competent and expert pieces, easily equal to the nearest high fidelity studio. mature works of his leading contem poraries 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 PRODUCTS

• Reverberation Unit. Both the inconveni­ eration, the R701 features a variable band­ vere shock, vibration, and acceleration. e nce and expense of echo ch ambers are w idth i.f. channel which permits selection Available in standard resistances of 250 to of maximum wide-range r esponse or maxi- 10,000 ohms with power rating of 0.25 eliminated through u se of the new Model watt, T rimpots are manufactured by 40 Reverberation Unit, recently announced Bourns Laboratories, 6135 Magnolia Ave., by Audio Instrument Company, Inc. , 133 Riverside, Calif. W . . 14th St., New York 11, N. Y. An im­ prove d version of the Goodfriend-Audio Facilities Co. artificial r everb e ration gen­ • Prea.mp and Matching Tape-Transport Mechanism. Designed for installation in erator which was first introduced three custom cabinets, t he new Pentron Model years ago, the unit is a multiple-head mag­ PRE-7 preamplifier and Model 9T-3M t ape netic-tape-loop device which is compact. transport mechanism make up a complete convenient, and flexible in adju stment. In tape recorder and p layback assembly for opera tion, the input signal is recorded, use w ith any existing audio system. then reprodu ced by several magnetic hea<\s Preamp control panel is equipped with

mum selectivity. A 10-kc whistle filter eliminates inter-station interference. The t uner is equipped with continuously vari­ able bass and treble controls and a 6-posi­ tion function-selector switch. Among other no table features are: a built-in preampli­ fier with compensation for GE, Pickering, a nd Audak pickups; cathode-follower out­ put circuit, and a utom a tic reduction of voltage on all but a udio t u bes when tUller is u sed with phono input. A udio output is 3 volts at 6000 ohms, with only 0.2 per at different times. The r eproduced signals cent distortion. Freque n cy r esponse is are returned to the recording head, and within ±0.5 db from 20 to 20,000 cps on passed around the recirculation l oop again FM, from 20 to 4000 cps on n ormal AM, with diminished amplitude. In this man­ and from 20 to 7500 cps on broad-band n e r, 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., N ew York 14, N. Y. room. A switch control permits c h a nging the number a nd position of reproducing • Compa ct High-Fidelity 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, d esignated dir ect sound may a lso be w idely a ltered. M'odel LJ2, features frequency r esponse 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 'h per cent system circuit chan ges are necessary. and intermodulation is 4 per cent. Inputs motor switc h, pilot light, magic-eye re­ Supplied for rack mounting on a n 8 %. x 19 cording level ind~cator, tape-radio switch, panel. volul':le-tone control, p lay-record switch, and Jacks for phonograph, t une r, micro­ phone, ou tput, a nd monitoring. The trans­ • High-Output Magnetic Tape. Many i m ­ port unit permits choice of 3.75-in. or proved qualities are inhe rent in the new 7.5-in. r ecording speed. Separate r ecord No. 120 "Scotch" recording tape recently and eras~ heads h ave removable pole annou nced by Minnesota Mining and Man­ pIeces whIch can be replaced as simply as ufacturing Co., 900 F a uquier St., St. Paul a phonograph needle. Fast forward and Minn. Offering more tha n twice the output rewind will transfer a 1200-ft. spool in 40 of previous Scotch tape, the n ew t ape 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 u se. Complete technical specifications will be malled on request to The Pentron Corporation, Dept. AE- 3, 221 E. Cullerton St., Chica go 6, Ill.

• Low-Cost VTVOM Kit. Frequency r e­ sponse as high as '2.5 mc, adequate for servicing TV circu its as well as a udio are supplied for m agnetic pickup, micro­ equipment, is one of the features of the phone, crystal pickup, and tuner. Treble new E:night vacuum-tube voit-ohm-mllli­ control a ffords 18 db cut at 10,000 cps. a mmeter kit recently announced by Allied Bass control permrts 15 db boost at 50 cps. Radio Corp., 833 W. J ackson Blvd., Chi­ Hum level is 80 db b elow 8 watts. Output cago 7, Ill. Among its 29 r anges a re six impedances are 4, 8, and 16 ohms. Com­ p)e.te inf ormati~ n will be supplied by Pre­ CISIon Electrol1lcs, 9101 King Ave., Frank- 1m Park, Ill. •. Sma.ll Wire-Wound Potentiometer. De­ sl!m.ed f.or precise circuit trimming in and r ecording s~~dios, in computer work, mll1laturlzed equipment, t h e n ew Bourns and III 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 th.an tapes previously marketed, thus per­ are made by turning a n exposed s lotted m l ~ting an 8-d~ greater signal-to-noise ratIO on conventIOnal professiona l t ape re­ shaft with a screwdriver. R esolution as corders. Of particular value in the sou nd recording field, the new No. 120 tape will permit improved quality in recording s, wIth greater dynamic range. Aside from the fact that it is da rk green in color and employs a coating material with increased magnetic remanence, It is identical phys­ ically .with conventional tape. It may be used Illterchangeably with conventional tape without bias adjustment.

• High-Quality FM-AM Tuner. Remark- ' able sensi tivity permits excelle nt FM re­ ception in areas where it h as h er:etofore been impossible with the new Bogen Model R701 14-tube tuner. Designed for high­ q u ~lity custom installations, the tuner re- 9-Ulres only a 3-mv input for 30 db quiet­ ranges for measuring a.c. peak-to-peak ~ng . P u s~-button control permits switch- volts, six milliammeter ranges, and five 1,:\ or s~lt c h-0':It of a .f.c. action. Protec­ low as 0.2~ per cent is obtained over the capacitance ranges. Maximum d.c. ran ge is tIon agamst dr Ift is afforded by tempera­ 2.5 -turn adJustment range. E lectrical set­ 1000 volts, and maximum a.c. range is 2800 ture-compensated oscillator. For AM op- hngs are securely maintained during se- volts. Resistance and capacitance ran ges 54 AUDIO ENGINEERING • MARCH , 1953 are 1000 megohms a nd 5000 microfarads, respectively. Special probes are available for extending the d.c. range to 30,000 volts and the a.c. frequ ency range t o read r.f. to 200 mc. All voltage functions are elec­ DESIGNED FOR HI-FI PERFECTION! tronica lly protected against burnout. • Intercom System. A baseboa rd-mounted TANNOY 12" DUAL power s upply, self-compensating to de­ liver required power to a ll or a selected group of stations, is featured with the CONCENTRIC SPEAKER new 20-wa tt Redi-Power Talk-O-Phone, recently introduced by T a lk-O-Phone Co., 130.00 net 1512 S. Pula ski Road, Chicago 23, Ill. Internationally acclaimed for amazing response range, balance Although r etaining 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. GARRARD RC-BO 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 11 0 or 220 V. Complete with 45 RPM spindle and two empty shells. BOGEN R701 earlier m odels, the new T a lk-O-Phone of­ fers a number of a dditiona l engineering features. Uni-Trans dictation control elim­ FM-AM TUNER ina tes the n eed for operating any controls while dict a ting. Twelve, twenty, thirty, or 145.20 net forty station capacity can be housed in the sam e cabinet, a nd the system can be Full frequency range of 88-108 MC on FM, 530-1650 KC on AM; expa nded or a ltered a t any time without discarding the original equipment. frequency response of 20-20,000 cps. ±.5 db on FM ; built in pre-amplifier, AFC, AFC • FM-AM Tuner. N ew est in the line of defeat switch, low distortion; hum level - 65 db below. 14 tubes including power sup­ high-fidelity components m a nufactured by ply. Size 15" x 8Yz" x 9". Weight, 17 Ibs. The Pilot R a dio Corporation, Long Island City, N. Y., is the Model AF-723 Pilotuner, an 8-tube self-powered unit which incor­ CONCERTONE 1501 D porates a temperature-compensated oscil­ lator for drift-free FM reception, a lso a.f.c. TAPE RECORDER which m ay b e switch ed in or out at will. 345.00 net New and improved! Separate heads for high frequency erase, record and play back, with simultaneous monitor­ ing from tape while recording. Instantaneous choice of 7 11z" or 15" per second tape speed. Three synchronous, dynamically balanced motors for dependable perform­ ance. Frequency response ± 2 db, 50 to 15,000 cycles at 15" per second. Available in single or dual track. Carrying case and monitoring amplifier with 8-in. speaker ." .. . " ...... ' ...... ' 82.50 BOGEN H010-RXPX Inpu ts are provided for TV and phono. REMOTE CONTROL Tone control on the AF-723 may be switched out when the tuner is used with AMPLIFIER an audio amplifier which incorpor ates such 147.15 controls. Cathode-follower output permits The famous Bogen Baton combines an all-triode power u p to 100 feet of interconnecting cable to amplifier and remote control. Power output 10 watts, amplifier without detracting from audio fidelity. The tuner is supplied with a hand­ peaks to 25; frequency response : ± 1 11z db, 10-20,000 some bronze-finish escutcheon plate for cps; Hum: 70 db below; speaker output: 12 ohms; 8 ' . custom cabinet installa tion. Over-all di­ tubes; Inputs: GE, Pickering; tuner; Controls: bass, treble, power on-off, selector; size: mensions are 14 x 7 'I. x 8'h in. 15" x 10" x 8"; weight: 32 Ibs. 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 SERI ES CARTRI DGE vises us of erroneous figures on his Fig. 3. 47.50 The values for T along the top should Here's unbelievable freedom from needle talk! Equipped with a dia- have been: 1.59, 3.18, 4.77, 6.36, 7.95, 9.54, mond stylus .. . the cartridge is of the moving coil design. 1.0 mil tip. 11.1, 12.7, 14.3, and 15.9. The values for F 215C-3.0 mil tip .. , . ,." . . ... " ...... , .. " ,. , ...... , ...... 42.50 along the left side of the diagram should 215B-2.5 mil tip ...... , . . ... , . . , .. . , ...... , ... , . ... , . , . , ...... , 4~.~0 have been: 100, 50.0, 33.3, 25.0, 20.0, 16.7, For vertical records ...... ,...... 5 . 0 14.3, 12.5, 11.1, and 10.0. Mail & Phone Orders Fill ed .. • 25 % Deposit, Balance COD Lewis S. Goodfriend, author of "The Send for FREE Catalogue, Music of the Masters Wide Range R-C Oscillator," also in the 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 j unction of R, and the 0.5-l.I-f RTLANDT ST., NEW YORK capacitor should be a 1.0-meg resistor Dept. A 43 rather than a solid wire. In Fig. 3, page l/uJio. Mad 68 the top cathode resistor should have CORTLANDT 7-0315-9 be~n 160 ohms, and the 1.0-meg · resistor The Ho use Bu ilt on Service should have been shown as described above in Fig. 2.

AUDIO ENGINEERING' • MARCH, 1953 55 PATENTS [from page 6] often synonymous!) into action. With high-quality audio going strong after the buildup in interest it has undergone since the war, many of us seem to be finding that the quality in the best audio amplifiers today leaves little to be desired and our­ selves 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 fre­ quency bands-up to 100 kc and more. In most cases the on ly valu e 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 transcrip­ tion ? A video amplifier is essentially a tion pre.amplifier. resistance-coupled amplifier with extremely • EXCE LLENT FREQUE NCY RESPO NSE - Features low wide band-to at least 4 mc, generally, and distortio n and noise level. sometimes a great deal more. As the word video indicates, the principal use for such • COMPACT .•. YET HIGHLY ACCESSIBLE. amplifiers today is in amplifying television The G-E Plug-in Broadcast Audio line includes: picture signals; but that is by no means BA-l-F BA-12-C BP-10-B the only use. Meantime, any good book on PRE-AMP PGMjMON AMP POWER SUPP LY television will give the basic approach to For information write: General Electric Co., wideband amplification, from which some Section 4433, Electt'onics Park, Syracuse, N. Y. audio might well jump off to new ap­ proaches and better results than present circuits. GE NERAL. ELECTRIC The apparatus required is simple enough -the same old tubes, resistors, capacitors, and the like. A couple of new components come into play- coils with small induct­ \0'" High fidelity Record Reproductio_n....-___..-:~ ances, up to a maximum of around 1 milli­ henry. They are easily wound or bought . .. Wideband osci lloscopes are available today, C» though they are a little expensive usually. ~ But a long series of investigations, experi­ c:: mentation, and self-indoctrination can be ..::= had by playing with the family TV receiver . U Better yet, get an oid, second-hand receiver, derive signal from some convenient point ""c:: in the good set (that won't harm it any ..o way) and transmit video from the good set u 7, 10,. AND 12 to the second-hand one via video amplifiers, C» INCH RECORDS attenuators, phase inverters, frequency-cor­ ~ P4~ rection networks, and all the rest of the possible gimmicks. Video work is j ust an 3-SPEED RECORD CHANG ERS extension of audio and it has the perfect fie ld of play for the audio man with wide­ banditis. In future we are going to look fo r a few MODEL 3/ 522· good video-amplifier patents. We'll write Intermixes 10 and 12·inch records them up for .IE, see if Editor McProud LIST PRIC E $65.00 (less base) will print them, then wait for the brickbats MODEL 3/ 521· and bouquets in the mail ! Non·lntermix Model (Y01lre on Y01W own, Mr. D. We'll nil! LIST PRICE $54.50 'em., but on your l'esponsibility .. ED.) (less base) · Available in cream. brown or gray finish. AUDIO 1693 [jl-om 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). 4. To cause the diaphragm to have greater excursion; fasten a vessel (p) to the ring, and a funnel (y) to the ves­ sel. The incoming sound will be carried to the diaphragm. If one places the Anvil-forming ap­ pendage between the teeth he will pos-

56 AUD IO ENGINEERING • MARCH , 1953 sibly be able to perceive sound. At the "Strange Facts About the Behavior of very least, by looking sharply, he will be /<, J ~ .' Sound": able to see the movement of the dia­ - j phragm and the action of the hammer If one takes a large jug which has i:: ·;:~.:~ . on the anvil. \ been rinsed out with wine and drops a ~~ . '.,;.:~:~:;~::~~;~ piece of li ghted paper into it a fantastic Reverberation and Damping and awful sound is said to result. The principle of the anechoic chamber T he phenomenon referred to is that appears in this analysis. of a Helmholtz resonator responding to There are variou~ ways by which a stimulation by a w ide frequency spec­ body can be made to lose its sound: I ) trum of noise, and emphasizing those when thrust under water, 2) when sur­ sounds which li e in the frequency range rounded by soft and absorbent mate­ of enclosure resonance. H ad Ringel­ rial . . . Cloth wrapped around clavi­ Fig,S. A military horn supposed to have been 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 undel'stand a lecturer or hear music well when the auditorium is full of people. Sound waves are absorbed and attenuated by the presence of people anG! their clothing. It is possible to drape an auditorium with wool or straw to such a degree that the human voice can scarcely be heard. T his is essentially the reason why the sound of bells is muffled during .a heavy snow-storm. It is not so much that the sound of the bells is reduced by virtue 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 ba re surfaces.

Fig. 4. Artificial hearing mechanism. The com­ bination of horn and diaphragm is prophetic of 19th century phonograph design. "BALANCED" Military Applications of Sound TV TRIPOD mounted on During wars, advance patrols report 3-wheel We THREW THE book aw.ay and engineered a that they can hear the sound of cavalry portable over 1,000 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 horn of Alexander the dolly graphic and video need. The result-a revela­ Great, made by Aristotle, was able to illustrated. tion in effortless operation, super-smooth tilt proj ect 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 12Yz miles away. (See Fig. 5) closed, rustproof, needs no lubrication. Ten- sion adjustment for Camera Man's preference. Legal and Humane Considerations 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 operation out of this kettle. Nowadays, unless one gives ample warning when throwing something from an upper window out into the street, he WE DESIGN and manufacture Lens WE CALIBRATE LENSES . • . Precision 'T' STOP CALIBRA­ may be sued for damages. Mounts and camera equipment for TION of all type lenses, any focal length. Our method is From which we may conclude that approved by Motion Picture Industry and Standard Com­ 16mm - 3Smm and TV cameras. courtesy and grace were not unknown mittee of SMPTE. Lenses coated for photography. in 1693. Special TV coating.

Legend and Hearsay WE RENT AND SERVICE

Ringelmann's thesis 1'eRects ;a, culture CAMERAS -I< MOVIOLAS -I< in wkich the scientific attitude was just emerging. It conta ins much pe'rceptive DOLLIES ••• Complete line analysis and imsight, but the a uthor also of 3Smm and 16mm equipment available for rental. It will pay you to get to know us. retains some 0f the disdain of Scholas­ The country's foremast ticism for experimental verification; and MITCHELL: Standard, Hi-Speed, BNC, NC, 16mm. Bell & professionals depend upon our he is often content to cite unchecked HOWELL: Standard, . Shiftaver, Eyemos. MAU'RER: 16mm portable, versatile, adaptable lege1'ld or hearsay, even when he could Cameras. ARRIFLEX. MOVIOLA: Editing machines, Synchronizers. equipment_

AUD'tO ENGINEERING • MARCH, 1953 57 WHY PAY RENT on your echo chamber? FIRST INVENTOR Goodfriend-Audio Facilities Reverberation Unit [from page 40 ] now made exclusively ventor to discoveries disclosed in his in improved form by 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 a magnetic tape loop sys­ presented," said that court, "whether on the issue of prior invention it is the tem with FIVE HEADS claims or the disclosure which counts. (Model 40) or SEVEN On principle it would seem that the 3 " PANEL HEADS (Model 42). / 4" X19 Switching heads produces claims were the place to look for the AN ECHO CHAMBER ON AN 8. invention. The disclosure, so far as it Compact: Single 8 %" x 19" panel. vanous 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 time: Continuously adjustable. 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 . ~ d. INSTRUMENT which it will be profitable to follow. ~U 10 COMPANY INC "Without some such selection the art Model 40: $985.00 is left without cue for omission and must Dept. 7r 133 WEST 14th STREET, N.Y. I I ,N. Y. Pays for itself in 3 to 5 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 combina­ tions which will read upon the disclo­ sure such as are new and useful. "Therefore, at least presumptively, the 'invention' must be found in the 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 part of the patent or application which in the Field 01 Sound Reproduction sets out what combinations of the ele­ ments disclosed the applicant says are If you are novice, hobbyist,. experimenter, or engineer ... if you his new and useful contributions to the art." are a lover ·of music ... and in pursuit of sound, undistorted The discoverers of this process for ... Audio Engineering will be your faithful, reliable com­ acetylene welding appealed and the de­ panion all the way. You will find no more pleasureable and cision of the Federal District Court was affirmed by the Federal Circuit. Court /stimulating reading than there is in AE; absorbingly interest­ of Appeals, which stated, ing material, valuable and authentic cfata, workable detailed in- "Thus the question is narrowed to structions ... all comprehensively and yet practically presented. this, does the 'first inventor' of the fo urth 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, suffi­ cient 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 j------intellectually a part of the invention. I "We hold that a 'first inventor' within MAIL this: AUDIO ENGINEERING the meaning of that phrase as used in P. O. Box 629, Mineola, N. Y. the fourth defense, must be a person ' Coupon l Enclosed is 0 Check 0 Money Order for $ . who perfects his invention. No inven­ Please send a copy of each new issue of Audio Engineering for the next o 12 months; 0 24 months to: tion can be intellectually perfected un­ Please Print less it is thought out and concluded and NOW+: Nam.' ______.______the only evidence of such perfected in­ Add,." ______vention ordinarily derivable from any patent is a union of disclosure and " __Ii.'iII1i'B_ City Zone__ __State ______• claim." Subscription Price: U.S.A., Canada and Pan American Union: 1 year .. 1 $3.00 2 years . . $5.00. Other countries: 1 year . . $4.00 2 years .. $7.00. When the appeal from this decision IL ______came before the United States Supreme Court a year and a half later the court

58 AUDIO ENGINEERING • MARCH, 1953 reversed the decision of the two lower courts on the opinion of Justice H olmes who established at that time the defini­ tion of 'first inventor' that is now made a provision of the patent statute itself . . "It is not disputed that the applica­ tion gave a complete and adequate de­ scription of the thing patented but did not claim it. The patent law authorizes RESEARCH a person who has invented an improve­ ment like the present, 'not known or DEVELOPMENT used by others in this country before invention' to obtain a patent for it. .. . The fundamental rule, we repeat, is that SERVICE the patentee must be the first inventor." on REFERENCES Detrola Radio & Television Corp. v. Hazel­ Diamond* Sapphenoid§ 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 burn Co., 297 Fed. 846; 1 Fed. 2d 227; Acetate Disc Sapphire Cutters 270 U.S. 390 Magnetic Film Diamond Scribers COLUMBIA "360" Magnetic Tape Sapphenoid Guides [from page 29J To Your Specifications tances and locations. The resultant curves were integrated and then aver­ t)~ LadMato'tfl aged to yield the -one illustrated. Very Since 1928 close correlation can be found between the sound characteristic thus derived P. O. Box Hp" Phone STate 4-0881 and the actual performance of the player in the home. Encino, California The amplifier has been designed to §Synthetic *Genuine give adequate performance for a maxi­ mum power output of about two watts, as shown in 1:he distortion curves, Figs. 6 and 7. The ampli fier frequency re­ sponse has been shaped so that when combined with the other components of the system, the over-all sound pressure ~e~ diagram is the desired one. Figwre 8 shows the frequency response of the pickup by itself. IfMPLIFIER ··: ~lT. During the development of the Colum­ bia "360" in the CBS Laboratories Divi­ FEATURES sion we had to rely on the support and inspiration of many. In particular, the writer is indebted to Thomas Broderick, Richard Mahler and Rene Snepvangers for their wholehearted cooperation and many useful suggestions.

I- -- i- :?,"fr I- I- - ~ ~L - ~ - - r-- - -

W·2 Amplifier Kit (Incl. Main Amplifier with Peerless Output Trans form· " pr~ea~;?rfl~~P~1t) an~hi~~i~~ $69 50 I-+-H+t+I I-- - - -H- -t- ++++I-,llti l__ Weight 39 Ibs. S hipped express _ only. Hili ._ W-2M Amplifie r Kit (Inc1. Main Amplifier ' REOU[NCY IN CY(:L I!5 1' 1:" SItCONO with P e erless Output Transformer and Power S upp ly) Shipping $49 75 Weight 2 9 Ibs . Shl.ppOO express _ only . Fig. 8. Typical response plotted against the W -3 Amplifie r Kit (IncI. Main Am plifier' with Ac rosound Output Trans- electrical curve of Columbia 103 test record . fo rmer, Power Supply and WA- PI Pre amplifie r Kit) Shipping $69 50 Weight 39 Ibs . Shipped express _ only. REEVES APPOINTS NEELY W·3M Amplifie r Kit (Incl. Main Amplifier with Acros ound Output Trans- former and Power Supply) S h ip' $49 ping Weight 29 Ibs. Shipped ex-75 _ Products of Reeves Soundcraft Corpo­ press only. ration, New York, will be distributed to WA- Pl Preamplifier Kit only. Shipping Weight 7 Ibs . Shipped expres s the electronics industry in the Southwest or parcel p ost. $19 75 by Neely Enterprises, Inc., Los Angeles, . effective at once, according to Frank B. Rogers. J r., Reeves vice-president.

AUDIO ENGINEERING • MARCH, 1953 59 MAGNETIC PICKUPS [from page 20] from 10 to 50 iLiLf in the input wiring, cutoff frequencies are shown in Fig. 5, plug and socket, and switch (if used) in for each of the fo ur pickups calculated. the preampli fier. For any cartridge at any desired cutoff From all this, it is apparent that a frequency the values of RL and C may total shun t capacitance of at least ioo be read directly from the left-hand iL[J.f is assured for any installation. A scales. long run of shielded wire between the Fig~wes 6 to 9 inclusive show the ef­ turntable and preamplifier with the use fect of capacitance only on each of the of high-m u triode tubes can easil y bring fo ur pickups. A wide range of values was used, to cover the range from the total capacitance to 1000 [J.[J.f or 5000 to 20,000 cps in each case. From more. Nearly all practical installations all of these curves it will easily be seel~ 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 10-7 and 2 x 10-'. minals.

TABLE II Miller-Effect Capacitance of Input Tubes

Tube Type C GO C GP Amplification Total Capacitance-!'ILf 6SN7 (6)5 ) 3.0 4 .0 15 63 6SL7 3.4 2.8 52 159 6S17 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 III Equation (1) was reduc(ld 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-l1l1f per foot pickups under various load conditions. Shielded hook-up wi re 55 - 70 T he response calculations we re divided .1 40 O. D. Microphone into the foll ow ing classifications: cable 40 .200 O. D. Microphone (1) RL = w, C varied. cable 25 (2) C fixed, RL varied. Heavy duty Mic rophone ( 3) RL and C chosen to provide the cable 33 sharpest cutoff at certain frequencies. It will be observed that Land C form The amount of rise at the peak de­ Triad Power Transform ers-like a low-pass constant-K fi lter 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 and RL to satisfy the relationships : in that respect. F urthermore, the loca­ you want it-on the decal. tion of the peak depends on the induct­ It simplifies in stallation-speeds RL 1 ance of the pickup coil, fo r a given ca­ servicing-makes reordering easy. L= - f and C= - f R (3) ]to 3t o L pacitance. In general, therefore, the Whether used for replacement, higher impedance (hence higher induct­ indu strial ap plications, PA amplifiers The values of R" and C for various ance) pickups are more sensitive to or amateu r gear, they offer small size, maximum efficiency, low temperature rise and low cost. Also, they are "Climatite" treated, 0 .1 O.1 AUDA K CL ARKSTAN -= I=- - ~ both coil and core, for prot ection mh ,,- +-L z 720 ml'! == !== L -7 80 ~ against moisture and fo r elimination R = 1660 ohm s - I-- R"' 630 ohm_ , ~ I-- " of lamination cha tter. Laminations G. E. \, PICK ERING "- - f..- are pa inted to prevent rust. Copper t o< 470mh '." L R 1S0mh ' .\ C -\.lId R z 600 ohm. straps are used for static shie lds, .0' OOK' R· 370 ohm. .01 100K' f\ grounded to case and core.

Lea ds are co lor coded, UL approved. 1/ Final te sts include checking for .r: ... '\ 2 0 K '. proper operation . Cases are '" ~'/ 1(,,[> .- " fin ished in durable, attractive .001 10K .00 1 110.K "'" V grey baked enamel. '1-" Write for Catalog TR·52F 1/ .... ./ "'i!lifIIIII'lI ," 1/ 1'\ f'( .0001 " .0001 ~ \ . 1000" 10000 20000 1000 10000 20000

FREQUENCY - CP I FREQUENC Y - Cpt

Fig. 5. Values of Rr, and C fo r various cutoff frequencies for the four pickups.

60 AUDIO ENGINEERING • MARCH, 1953 shunt capacitance effects than are the lower impedance units. In the very-high-impedance units particular care should be taken to re~ duce shunt capacitance, since even 100 or 200 fLfLf will have a significant effect on the response above 10,000 cps. The addition of a shunt resistance makes it possible to flatten out the reso­ nance peak, but it is not possible to ob-

II +10 2 10~~ ~,- P:"'l 100 ~~f ~ ....- ~ V~ r-")~ I 0 PD? I- \ ::> 1\ O~l Q. I- ::>o ~ -10 w > °0 ~ ~ ..J :t£ ~;,-" W a: -20 1 I ~ AUDAK \: Rl :r CD_: , , . , . . 20000 1000 10000

FREQUENCY - cpa

Fig . 6. Response of Audak L-6 pickup with various shunt capacitances and a resistive load of 00. tain any significant response above the cutoff frequency. Figures 10, 11, 12 and 13 show the ef­ fects of adding resistance in parallel with the shunt capacitance. It is appar­ ent that a value of resistance can be found to give substantially flat response out to the cutoff frequency, but the up­ per frequency limit is definitely fixed by the prodt!lct of coil inductance and shunt capacitance. When the values of RD 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 cate the kind of result to be expected ANNOUNCES with each of the four pickups, Fig. 14 Grand Opening New York's Largest Audio Center I I · .OOO2~' 650 Sixth Avenue +10 FEATURING / ~ ~oC ~/ NOT 1 ... NOT 2 ••• BUT 3 I­ ...... :::: ::> o Q. I- ::> o I ~ ~ -10 i= I\~ * Conveniently located for easy a ccess from ­ « '0 any part of Metropolitan New York ..J w 0", * Staffed by qualified personnel !o help cr :t£ :~~... solve your audio probloms I I * The most comple!e display of all fines! make-s of audio equipment G.E. CARTR\DG.E * Visit us today and see why Sun Radio. sets the standards for the audio industry RL = Q) * Ge! your free copy of Sun's 1953 Audio I Equipment ·handbook. 100 of the most , , , . . 20 000 valuable pages any music lover could have 1000 10000

FREQUENCY - cpa

Fig. 7. Response of GE RPX-050 pickup with various shunt capacitances. RL = 00.

AUDIO ENGINEERING • MARCH, 1953 61 -.

. 0h1I~~ IJ 12bb!~, '500 Ii- 1\O~~' 200~~f _ .- +10 +10 L ,....,J ~ ,4~'~ ';Ute4t S> ... v:~ ....-::::: .....-:: ~ - ,;; ~ o :Yo~- I- 0 \ 'Q- ::> 100~~1 ~ "- , I- I­ l\ : o~ HIGH ::> :> o "- ~, 5 - 10 ~-10 I\~' o '<', FIDELitY ~ ~ UJ \o~ ..J > EQUIPMENT UJ It: :q;. \ ~ -20 5-20 UJ '\ PICKERING 120M It:

RL = CD -30 , , . , . . 2 0000 =£h 1000 10000 CLARKSTAN

RL = CD FREQUENCY - CPI I . 20000 1000 10000 Fig. 8_ Response of Pickering D120M pickup FREQUENCY - Cpl with various shunt capacitances. RL = co. $29·?~a l HI -fi Fig . 9. Response of Clarkstan pickup with Mod el 501 various shunt capacitances. RL = co . Compact .. high-fidelity corner speaker system, deyeloped was prepared, using values selected at the famous Mass. Institute of Technology. Baruch­ from Fig. 5 for a cutoff frequency of La ng principals approach acoustical qualities of larger the rate of attenuation above cutoff is units costing four times this low price. Small space 5000 cps. As might be expected, the very close to 12 db per octave. re~u ire ments, high output and wide dispersion angle, sharpness of cutoff varies from .unit ~o make it perfect for low cost, high fid elity mu,ic systems In order to check the equations which In homes, public building s, restaurants, schools. Con­ unit according to the Q of the coIl. ThiS were used to obtain the foregoing re­ nects easily to phano systems, F M-A M rad ios, TV . Q cannot completely be represented by Resp.n", 40 to 12,000 cps at plus or minus 3 db . sponse curves, actual measurements 1.3" high, 19" wide, 9 %" de ep, Wt. ten Ibs. 4 ~ where L is the coi l inductance and were made by two methods: the pickUps ohms impe d a n~e . were tested on a standard frequency Brilliant New Hi-Fidelity! R the coi l and lead resistance. The ac­ record, and they were also checked by tual Q depends on the a_c. losses (eddy the simulated-signal method_ The meas­ PILOT FM-AM TUNER currents, hysteresis, etc. in the soft-iron urements made with the frequency rec­ - l' :l Self-contained power sup­ magnetic structures in the pickup) as ",J'.'/" .- ;: . . ply. With tone controls In ord gave close agreement up to 10,000 - " fi at position, ' audio fre­ we ll as the d.c. resistances. However, it , ' quency response is within cps, and increasing spread, of a random . c ... .. plus or minus 2 db. Max. was fo und that in devices of the type nature, above that frequency. This is to \. " • • -..!" \j"':'- ...... , undistorted audio output is being discussed here, the discrepancy be expected because of the high prob­ \ Ii.,;. :6 ~ ,... 7 volts. Model AF-82lA. between calculated and measured re­ ,0~ $99.95 able error in this method of measure­ PILOTONE AMPLIfiER Model AA902 .• _. _. $42.50 sponse was less than the probable error ment discussed earlier. PI LOTONE AM PLI f I ER Model AA901 . _ . . . . $99.50 of measurement. The second method gave com.plete PILOTONE PREAMPLIFIER Model PA911 ___ $29.95 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 best tonal quality. Re- 10 W. from Fig. 5 ; Fig_ 15 shows the results Conclusion mote control pre-amp amp & has inputs for tuner, pre-amp for 3000-, 5000-, 7000-, and 10,000-cps It is evident that the load impedance cutoff frequencies. It will be seen that across the terminals of a magnetic pho­ ~~gle ~~assr.h ~~~its. o~ $222 position stepped bass nograph pickup will have a great effect and treble control cir­ cuits. Frequency re­ sponse: 15 to 30,000 cycles .. AUDAK L-~ I I CLARK~TAN 1 G_ E_ Variable Reluctance +10 - WITH .002 CAPACITANCE CARTRIDCES ~ ~\ GE RPX -050 dual reversible sapphire strlus .. 8 .37 +10 ~ GE RPX-05l Same as RPX 050 (less stylus) 5 .28 ,.....~ o """~ 4 ~~ GE RPX-052 Combination diamond and sapphire ..,S> stylus ...... _ .. _ ...... 23.37 , -:::-- -:g:I\ -...... 5"~ GE RPX-040 with .003 sapphire _ .. _ .. _ . . . 5_97 I- --::::: ".., GE RPX -On wHh .001 sapphire _ ... _..... 5.97 :> 0 "- "- GE RPX-042 (Jess stylus) .. _ .. _ ...... 4.35 I- -I--- "'- ~ .. -10 :> ::> GE RPX-046 Professional type (Jess stylus) _. 6.87 0 ::::::'"" Q. GE RPX-047 Broadcast type (Jess stylus) _ .. _ 9.27 I ~ .. ~ ::> I- UJ i' o > -10 ;:: AeRO TRANSFORMERS ~ -20 m .. f02~R: ~ ..J i All Models fully potted UJ II: !i REtST'ANCE , TO -300 for ultra linear $24.75 ..J 1-1 Nd " ~ W 2 10~000: OHt\4S TO-290 15.75 TO-270 11.75 -20 . 1 = NO RESISTANCE a:: TO-3l0 _... 18.75 TO- 260 _ .. . 11.75 -30 t-3 50,000 ,OH,",S " 2 = 50000 OHMS TO-380 . .. _ 14.50 TO-250 .. . . ~ 11.75 3 = 20000 OHMS 4 20000 OHMS r- 5 Address Orders To Dept. AE 3 4 = 10000 OHMS 1~000 ;oH1S Write For FREE Booklet " Hi-Fi Magic" 20000 1000 10000 • 20000 1000 ' 10000 g L I: :t ALE FREQUENCY - CPI FREQUENCY - cps 'W"RADIO PARTS CO., Inc. 311 W . Baltimore St. Fig. 10. Response 'of Audak L-6 pickup with Fig . 11. Response of Clarkstan pickup with shunt capacitance of .002 j.tf and various load shunt capacitance of .002 j.tf and various load BALTIMORE 1, MD. resistances. resistances_

62 AUDIO ENGINEERING • MARCH, 1953 G. E. G.E. CARTRIDGE CUTOFF FILTERS 1 +10 0 '/'3/21__ \ 1', i' ..." ~ ~ r'\ 0 "... .: , -10 r\ ~'\ :::> - r-. '" Il. Sr- .... " .... :::> :::> R= a:t Il. 1\2\ 0 .... \ :> ic ~R~ I ~ UJ -10 0 > -20 \ >= mI I I UJ I I I I .. > -' 100000 OH MS '- fc RL C UJ 2 ..>= I- _3 50000 'OHMS • -' '" -20 .'\ UJ 3KC 9000 .006 4 20000'OHMS' '" -30 1-: 5KC 15000 .0022 - 5 S ==: OOO ----..:. 't iOHi i - 3 7KC 21000 .0011 4 10KC 29000 .00054 , , , . 20000 1000 10000 J ~ lO' 20000 1000 FREQUENCY - CPI 10000 FREQUENCY - cp.

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

PICKERING on the frequency response of the device. This effect can be accurately calculated +10 for a given pickup of known coil resist­ ~ ance and inductance. A resistive termi­ "... ,:::::. / 3 nation causes a general drop in output ~ at all frequencies, the loss increasing at :>.: 0 ....Il. high frequencies. A capacitive termina­ -1 tion causes a peak at a frequency deter­ a - I-- UJ mined by the LC product, of a magni­ > -10 ~ >= tude depending on the Q of the circuit. ..-' ~, ~ A combination of resistance and capaci­ UJ -1 Nq RE~IST!"NCE '" 2 30000 OHMS "\ tance will modify the peak, and at one -20 - 3 10000 'OHMS specific set of values for each case will 4 5000 OHM'S constitute a constant-K low-pass filter. 5 3100 ,HM1S When the resistive shunt has a low , . , . 20000 value compared to the capacitive react­ 1000' .0000 ance, the effect approaches that obtained FREQUENCY - Cpl with resistance ·termination alone. The foregoing information can be used to guard against unwanted modifi­ Fig . 13. Response of Pickering D120M pickup cations of the pickup frequency re­ with shunt capacitance of .005 J.l.f and vari­ sponse, to determine the highest usable ous load resistances. frequency obtainable under a given set of conditions, to compensate for fre­ quency effects in other parts of the sys­ tem, and to reduce noise from records by using the low-pass filter effect. -1-- LABYRINTH AND CABINET. (less ... 0 = . speaker) in " o;;;;~ '. PICKUP UNDER mahogany o r ~r:" 'I' , TE ST .... H-P 2000 1 blonde oak, :::> I- , A. F. +-.JO;.:1VOOV°V--t-!;-...J;.,..,....~-'G1-f'l---+'-T_~_-, $120 Il. , .... , OSCILLATOR =h" v ,-:,~~u_.J '~ :::> I ? I 1.- 0 _10 2: 5 :r: ~~ VTVM UJ i~ KIT ONLY Rl-485, > c ~ ~'1 >= ~R~ h '\- I ..J -l i ~:.~ UJ -20 IX: ':::

Fig. 16. Connection of equipment to obtain 15KC I CU~OlF I response curves shown. Va lues observed check RL C wifh those obtained from frequency records. _ .- CLARKSTAN 23000 .0014"f 15-inch Coaxial ---- AUOAK 25000 .0013"f Speoker, $179-95 ...... PICKERING 4700 .0067.1 REK-O-KUT FIRE - x-G. E. 15000 .0022.1 I I I I IIII I Serious damage by fire was suffered by I 20000 1000 10000 the Rek-O-Kut Company, manufacturer of FREQUENCV - Cpl precision turntables, Long Island City, N. Y. on the night of January 31. Although production was entirely disrupted for a 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 CLI FFORD AVE., ROCHE STER 3, N. Y. and capacitors shown in the legend. functioning on a virtually normal schedule.

AUDIO ENGINEERING • MARCH, 1953 63 THEATER SOUND (from page 31)

Design of t he Main Case The surest way to cut and assemble Ideal for the sections of the wood cabinet w ithout BROADCASTING mistakes is to make a plan drawi'ng of its assembly to scale, similar to F ig. RECORDING 7 or 8. This is especially true if the PUBLIC ADDRESS plywood is of different thicknesses. In "The ultimate in micro­ phone quo/ily," says the cabinets we constructed we used ;;,; ­ Evon Rushing, sound in. plywood throughout, but the front engineer of the Hotel of the cabinet, sides, top, and bottom New Yorker. ' • Shaul right into the could be made of thicker plywood if it new Amperlte Micro. is on hand. All pieces must be at least phone-or stand 2 leel ;;'; -in. thick, however. away-reproduction Is always perfect. Figure 9 shows the metal horn at­ • Nol allecled by tached to the front by wood screws but any climatic conditions. this was our first assembly. In later • Guoranleed to with. models, the fin-like separator pieces pro­ stand severe "knocking aroul1d." ject at right angles from the center of each side of the sheet metal horn, to act as struts between partitions, and they are slotted across one side to let the 3/ 16-in. truss rods pass through them. These pieces must be shaped to fairly well match the surfaces they are to push against, and to obtain a snug fit so that partitions will not be sprung out of position as truss rods a re tightened. A truss rod passes from the side of 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 pass­ ages 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 infol'- 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 facilit ies for treatment while they ate tacked in place. F inally 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 ham­ mer. This end is used at the outside of the American Cancer Society. the cabinet with a large washer to keep You may mail it, simply ad­ the nut from seating into the wood with the vibrations. The other nut is screwed dressed CANCER, c/ o 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 install ing an 8-in. speaker frame on the larger magnet an additional 16- gao metal fl ange can be included in the assembly, as shown in F ig. 7, to form a ti e or hub for the partitions of the sound chamber. This member seals off the passage of sound to the rear and gives a more direct support for the AmeriCan heavy magnet. W ith our first woofer we used a wooden collar, fabricated by Cancer glueing two layers of Ys -in. plywood WRITE F O,R CATAL O G together, as shown in F ig. 8. One layer Society. ~ was given ~ -in. slots to let a 3/ 16-in. PRECISION ELECTRONICS, Inc. tie rod pass through on each side of the ~ 9101 King Avenue, Franklin Park, III. speaker magnet.

64 AUDIO ENGINEERING • MARCH, 1953 Where the metal horn fits through Before tightening the truss rod nuts the front panel and where the partitions in the metal horn, on the final

AUDIO ENGINEERING • MARCH, 1~53 6) [boom page 34] No talent or t raining HANDBOOK needed to splice a ny type of safety fi lm , . . . which is decoupled and remains at rest A typical inexpensive "console" speaker fo rever, the new, elec­ during purely treble stimulation. of 12-inch diameter uses a 6.8 oz. Alnico Analysis of the circuit of (B) in Fig. rric " butt-welded" mir­ V slug. Quality 12-or IS-inch speakers 9-5, one of the possible variations of the may use Alnico V magnets of several acle device does it two-cone, single-voice-coil design, is AUTOMATICALL YI 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 gies. afforded without danger of rubbing. The Prestoseal splices magnetic voice coil must therefore not warp f ilm permanently Distribution of mass at different fre­ easily, and the spider must have maxi­ quencies may also be achieved by the mum radial rigidity to keep the coil in in 10 seconds! use of separate speakers. The frequency the narrow path prepared for it. spectrum is divided into two or three 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 t he 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, how­ forced vibration over a given band of ever, for the greater convenience of . . . replasticized I Eli mi nates dis­ low-impedance coils, which used fewer tortion, drying out, no overlap or frequencies, an electro-magnetic system for converting the electrical signal into turns and heavier wire. Recently the double thickness, no cement, high-impedance design has been revived, brushes or scraping . Guarantees mechanical force is required. The fixed perfect fram e 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 fo r voice-coil im­ Brochure on request The greater the magnetic fl ux 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. damping. It is also necessary that the The common S-inch table radio speaker field be uniform over the area through has an impedance of 3 to 4 ohms, 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 signal and the magnetomotive force ap­ figures. plied to the voice coil. The value of the rated or nominal The usual magnetic structure is of the impedance represents the actual electri­ type appearing in Fig. 9-1, where only cal impedance of the loudspeaker at the slug is made of magnetic material. about 400 cps and at that frequency The field path between the north and only. The effective electrical impedance south pole of the slug is directed by the presented to the amplifier at other £re­ U-shaped iron structure and the pole quencres varies considerably. It is 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 of force to the metallic path, and the voice coil presents an increased im­ voice-coil gap then receives the full pedance to signals of higher frequency. concentration of lines when they must (See Fig. 9-6.) 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 Over 196 pages • . • the final merit of the structure is judged quency, referred to as the blocketl value·packed with the impedance. When the voice coil is al­ world 's finest Rad io, TV by the magnetic flux produced in the and El ec tronic Equip· gap, and its uniformity over the path lowed to move in the magnetic field it ment. High·Fidelity and becomes the armature of an electric PA Sound Equipment . •• of voice-coil excursion. The strength Amplifiers, Sp eakers, Tu­ of the maguetic fi eld at the gap is de­ generator, and a back electromotive ners, Record Changers, termined by the material and weight force is produced, opposing the input Recorders, Packaged Systems, Cu stom Fu rni· of the slug, the degree to which the signal voltage. Effectively, then, it is tu re, etc. for Profes· field in confined to the metallic circuit more difficult for the source to send sio nal and Home In· stallation. and gap by the magnet structure, the current through the voice coil, since size of the gap, and the saturation limit back e.m.f. must be overcome in ad­ of the steel. dition to the voice coil impedance, and Some years ago really powerful mag­ the source "sees" an increased imped­ nets could be produced only by field ance between the speaker terminals. 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 small amount of copper (Alnico V) speaker, less current will flow. T his is RADIO & TELEVISION CORP. the permanent magnet type of slug is illustrated in Fig. 9-7. 48 WEST 48th 51 • 212 FULTON ST. able to produce fields of high intensity. The increase is the value of the New York 36, N. Y. • Circle 6-4 060 • New York 7. N. Y. Earlier types .of Alnico, designated by motional impedance. Since in a given lower numbers, produce weaker fields. speaker it is determined by voice-coil

66 AUDIO ENGINEERING • MARCH, 1953 velocity, it is affected by all the com­ ponents 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 in­ dicated 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.

Individually tested. No WWFB leaves our works AUTHENTIC without being individually tested. Close limits set on WILLIAMSON PERFORMANCE shunt reactance at 50 c/ s. MONTHLY SUMMARY of product develop­ Accepted as the most efficient output' transformer ments and price changes of radio elec­ Series reactance at 5 in the world, and fo r which there is no U. S. equivalent, tronic-television parts and equipment Kc/ s; d.c. resistances and the Partridge-Williamson Type WWFB ensures the per­ suApplied by United Catalog Publishers. Inc.; formance intended by the designer. Covering the full 110 Lafayette Street, New York City, pub· interwindings insulation audio range it has the lowest possible distortion. It is lishers of Radio's Master. resistances at 2 K.V. now available to all-of·f the shel'f from all good job­ These REPORTS will keep you up-to-date in bers. I f in any difficulty write us and mention your job. this ever-changing industry. They will also Price bers name-Don't tolerate a substitute-get the trans. help you to buy and specify to best advantage. form er built for the job-the Partridge-Williamson. A. complete descript ion of most products will be found in the Official Buying Guide. Radio's $2600 AVAILABLE TO ALL Master- available through local radio parts wholesalers. ______d_ut_yO_p_aid______IM_M __ ED_I_A_T_E_LY __ F_RO __ M_S_T_O_C_K------Recording Equipment, Speakers, Amplifiers, Needles, Tape, Etc. ~ PARTRIDGE TRANSFORMERS LTD., TOLWORTH, SURREY, ENGLAND ELECTRO · YOICE- Increased prIce on Modcl 6-HD diffrac­ tion hor;, to $15.00 net. FAIRCHILD RECORDING EQUIP.-Added Model 650·C preamplifier at $47.50 ... Model 65l-B power supply I F YOU ARE MOVI NG at $51.00 net. and Model 652-C preamplifier at $4 7.50 net. Decreased price on Model 620-CL power amplifier Please notify our Circulation Department at least 5 weeks in advance. The Post to $190.00 net. Office does not fOt'ward magazines sent to wrong destinations unless you pay addi­ GA RRARD SALES-Discontinued multispecd transcription tonal postage, and we can NOT duplica te copies sent to you once. To save your­ turntable Model 20l/B5. GENERAL ELECTRI C-Added Model UPX-009, pickup self, us, and the Post Office a headache, won't you please cooperate? When notify­ and transcription arm at $9.33 net . . . Model ing u s, please give your old address and your new addl·ess. RPX-051 triple-play variable-relu ctance cartridge at $5.28 net, and Model RPX -042 variable-reluctance Circulation Department cartridge at $4.35 net. Discontinued Model RPX-04 6 broadcast type variable reluctance cartridge. RADIO MAGAZINES, INC. LOWELL MANUFACTURING CO.-Added " The Richmond" Mineola, N. Y. series of wall -type speaker barnes. Decreased price on P. O. Box 629 Model H-24 hi-fidelity decorative grille to $10.50 net. MAGNECORD-Discontinued Model PT7-A recorder mecha­ nism for portable, Tack or cabinet models . . . Model PT7 -AX. same as Model PT7 -A less case •.• Model Jor clear, con trolled sound in corridors PT7-CC, console combination. PRECISION ELECTRONICS-Decreased price on Model 100-llA basic amplifier to $41. 25 net, and Model LOWELL Bi-Directional 2l5-BA hlgh-fldelity triode amplifler to $99.50 net. (West coast prices slightly higher). SPECIFY] REEVES SOUN DC RAFT -Added Soundcrart 45-r.p.m. re­ Speaker Baffles cording disc at $.66 net. MARK SIMPSON MFG.-Increased prices on No. 52 series or tape recorders. Test Equipment RADIO CITY PRODUCTS-Added Model 345 super vacuum­ tube voltmeter at $47.50 net, and Model 8873 TV servlshop unit at $139.95 net. Discontinued Model 654 V.T. voltmeter ... Model 449A pocket multitester, and Modeis 447BK and 447BPK multitestor ldts. R.C.A.-Increased price on Model WO -88A, 5-in. oscil- loscope to $169.50 net. Tubes-Receiving, Television, Special Purpose, etc. GENERAL ELECTRI C-Added germanium diodes 4JAlAl at $1.95 net ... 4JAlA2 at $3.85 net . .. 4JAlA3 Corridor speaker installations, in ceiling or walls, give the best at $4.80 net ... 4JA2A4 at $5.30 net ... IN8I at $4.35 list and G7G at $2.00 list. Discontinued G-IO performance when equipped with Lowell Bi-Directional Speaker Baffles. Sound waves are series of transistors (G-lO, G-lOA, G-lOll and G-lOC>' . directed in a concentrated beam along the length of the hall, permitting low level RAYTHEON-Added special purpose tubes CK5670 at $7.00 Vlliume of clear, undistorted sound. Echoes are held to a minimum. Heavily loaded net . .. CK5750 at $3.25 net ... CK6212 at $7.50 net ... CK6247 at $14.65 net. Also added baffle housing reduces feedback, eliminates metallic resonance. Speakers are protected 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 $7.60 net. struction, available in five series to accommodate 6" to 12" speakers. SYLYANIA-Added 'rv picture tube 2lZP4A at $40. 00 net, .. special purpose tube 6BF71V at $4.45 net. Please write for complete, illustrated installation instructions, specifications and prices. Also added radio receiving tubes: 6T4 at $3.55 list ... 6BQ7A at $3.20 list • . • 6BK5 at $2.45 list .. 12B4 at $2.00 list. Discontinued SUb -miniature 3030 Laclede Station Rd., tubes 6BF7 and 6BG 7 and receiving tube 6BQ7. I n­ LOWELL MANUFACTURING CO. St. Louis 17, Missouri creased pri ce on germanium crystal diodes IN60 to $.75 net and lNl05 to $.75 net. In Canada: Atlas Radio Corporation, Ltd., 560 King St., West, Toronto, Canada

AUDIO ENGINEERING • MARCH, 1953 67 SELECTIONS [from page 24] SAVE control may not be able to compensate Discuss ions of aural balancer have for the characteristics of both the record indicated that approximately equal fre­ and the reproducing equipment. quency di stortion, geometrica lly relative It has been established by several in­ to the frequency mid-point, is more de­ 33~% 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 termined by a study of bass deficiencies This is our increase with each successively hi gher 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 pre-emphasis in recording is very It \\Ti ll be seen that the transition fl'e­ The more men in a Group, the more effective in reducing scratch, as the quency suggested for treble attenuation each saves. If you send 6 or more sub­ system intends it to be. is different from that for treble boost, scriptions for the U.S.A. and Canada, Th€re is however, an advantage in and conditions are likely to exist in they will cost each subscriber $2.00, 1/3 less than the price of a regular being able to introduce sharp cut-offs at which both are required simultaneously. I -year subscription. Present subscrip_ given points of the frequency band, since Such simultaneous compensation, how­ tions may be renewed or extended as records which have little or no fre­ ever is inherently barred when a single part of a Group. 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 re­ duced without the signal being severely • The only publication devoted Bass Boost entirely to Audio- penalized. Some types of distoration are also most pronounced in the range above The conditions requiring bass boost • Recording are: • Broadcasting equipment 5,000 cps, and sharp cut-off helps reduce • Acoustics such effects with least change of the sig­ 1. Decreased hearing sensitivity to • Home reproduction systems nal. Sharp cut-off at high frequencies, bass frequencies at low sound intensities • PA systems however, is incompatible with the other (Fletcher-Munson effect). • Psychoacoustics 2. Recording characteristics whose duties of the treble tone control, and (Plea,e print) bass turnover frequency is higher than should be accomplished by separate net­ the one for which the repoducing equip­ Name works. The general tone control must be ment is designed. limited in its scratch reducing role to a 3. Bass deficiencies in records. Add ...... 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 by F letc\1er and Nam ••...... •.•...•• • •••••••. treble response above one or two thou­ Munson makes it evident that the appar­ Addr...... sand cps. Attention is occasionally called ent frequency distribution of energy in to this characteristic when broadca ~ t given program material will vary greatly studio use of an incorrectly compensated p ••ltion ...... Company .•. . .. .•.. microphone produces over-crisp and at different intensity levels. If the ampli ­ "hissy" speech. The compensation re­ fier has a correctly designed compensat­ Nam ••...•...... •..••.••••••.. . quired for this type of emphasis is com­ ing network associated with its volume Addres • ...... •...... ••..•.. 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 Nam • •...... •...... •.••••.. an inherently subjective problem. Like level of the original program, and fur­ compensation for the Fletcher-Munson ther adjustment may be necessary. The Addr...... 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 Po.ltlon ...... 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. N ...... reality indicates that investigation re­ The purpose of volume compensation 6 Addr_ . . • ...• .•..•...... qui res a statistical technique. is not, of course, to straighten out the curve of frequency perception, (that's tile way the music sounds in the con­ Position ...... Com pany ...... 5 B. B. Bauer, "Crystal pickup compen­ sation circuits," Electronics, 17, p. 128, cert l1all) but to shape this curve at the Nov., 1945. reproduced intensity level so that the N.lRe ...... •...... ••.. . perceived frequency distribution is simi­ 6 It is suggested that a useful approach Addr_ • .•• • .•••• •••..•• •... • .••.. . would be to compile judgment data in lar to the perceived distribution at the which the jury compares various conditions original intensity. We may take 80 db B Po.ltIon .•. •...••• Company . .. . ••.. . . of tonal balance, both symmetrical and as the average level of a 75-piece or­ asymmetrical to 800 cps, with the full chestra heard from a good seat, and 50 Add $.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 1 Hugh S. Knowles, "Loudspeakers and RADIO MACAZINES, INC. balanced and unbalanced conditions, with­ room acoustics," The Radio Eng'illeerillg 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.) B Ibid.

68 AUDIO ENGINEERING • MARCH, 1953

I db 9 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 priate curves on the same horizontal the writer include a transition frequency ,4"'''' '1~ 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 transition frequency of 400 cps, is re­ Bass Attenuation quired. This is, of course, for the ex­ treme 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 is much less; during very soft passages 2. Accentuation and distortion of bass to 8 hours. the boost required will be more. We frequencies by reproducing equipment. 3. A weak treble which creates tonal must work on the basis of the average imbalance. levels. 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 SOO-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 duction of intef.lsity level from 80 db which values have been used) may be approximately achieved by a gentle at­ Air-Tone Sound & Re­ to 50 db will produce no 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 shat-per 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 tJM necessary shape of response curve, of bass cut. Bass accentuation in reproducing IIi1t-7 which may be read from Fig. 5 as a uniformly elevated plateau over most of equipment is most often associated with 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 PHILA. 2, PA.· RI-6-8388 nance of the speaker system below 100 If the record reproducing equipment cps. The effects of tone-arm resonance has only a single turnover frequency a and turntable rumble usually occur be­ for every application ... compromise value of 500 to 600 cps is low 50 cps. As in the case of low-fre­ usually chosen. Some records have been quency boost, we cannot furnish accu­ made with higher turnover frequencies rate compensation for equipment frail­ ~ as high as 800 cps. Thus a moderate ties at the extreme low end, but we can ATLAS MIKE STANDS amount of boost to add to that of the alleviate the condition in some measure. fixed equalization will on occasion be Aural balance of a weak treble ap­ called for. Such equalization, however, is pears to pemand a low transition fre­ required by a relatively small number quency. Probable treble droop occurs, of records. 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 From a professional _'-:.r,.. adequate compensation. 500 cps, maximum slope,' 6 db per octave. boom stond to a flexi bJe goose neck to a ti ny . Bass deficiencies in reproducing equip­ fltti ng-whatever your need , n ment, like treble deficiencies, alto tend mike stands and accessories­ depend on it, ATLAS has it for to occur towards the extreme of the you. Designed and manufoc· frequency scale. Most moderate quality Conclusion tured for highest stability, quiet, ease of operation, dura­ loudspeakers (see Fig. 2), pickups, etc., Figure 5 is a graph of tone-control bility. And backed up 100% do not show a significant drop in bass frequency characteristics chosen on the by ATLAS-world leader in mike stands, public address loud­ response until frequencies below 100 cps, basis of the above discussion. The speakers and accessories for 21 and then with sharply dropping curves. parameters vary from many of those in years. Compare them all at your dIs­ Here too compensation cannot be ade­ 'common commercial use in that the ref­ tributor-You'll make your next quate. erence frequencies are shifted away mike stand an ATLAS. Adjustment for the Fletcher-Munson from the spectrum mid-point, about one effect is pr000bly the mest 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. Figu1'e 6 is a tone control circuit with 9 "Frequency Ra1~ge and P;wer Consid­ values assigned to approximate these eratirms in Music Repreilliction," Je~sen Teclmical Monograph No. 3, Jensen Manu­ curves. Some allowance has been made factur~ng Company. Note that a level of ' f0r the fact that the transition frequen­ 50 db is less than 10 dB above the average cies are affected by the degree of boost random noise level in a city apartment. Ot- cut used by the opera tor.

AUDIO ENGINEERING • MARCH, 1953 69 NOW Hear This NEW CHECKLIST .-CLASSIFIED'-· Rates: lO¢ per word per insertion for noncomm ercial [from page 14] advertisements; 25¢ per word for commercial adver· tI5eme"ts. Rates are net, and no discounts will be only two or three and have them make allowed. Copy must be acco mpanied by remittance In pronounced angles with each other fUll, 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. 18. If a studio organ is photographed TIlE AUDIO EXCHANGE, INC. buys and with an organist, make sure each of his sells quality high-fidelity sound systems and hands is on a different manual (key­ components. Guaranteed used and new equip­ ment. Catalogue. Dept. lE, 159-19 Hillside board), the keys are depressed, some Ave., Jamaica 32, N. Y. Telephone OL 8-0445. stops are drawn, and the organist is looking at his music and not at the FOR SALE: Relt-O-Kut M-12. perfect condi­ tion with new LP feedscrew, Astatic WR-40 camera. With or without an organist, microphone, Chip-Chaser, ~75.00. TR-12 OP ­ tional, $75.00. Beekman 3-6587 or Box CM-1. use a diagonal shot and make sure the Audio Engineering. organ console and stop knobs or tabs 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 disc recorder. $100. Brush 3-hour wire recorder, original cost microphones like the RCA 44BX and $800, excellent condition, $185. Reco·Art 74B and the Electro-Voice V series Company, 1305 Market St., Philadelphia 7. Pa. show up best with one of their dead The heart of a fine loud speaker is its pow­ ASSEMBLING A SYSTEM? Beat even erful magnetic structure. Jim Lansing faces toward the camera and the micro­ 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. . up well in almost any position. magnetic beam across the voice coil 30% DISCOUNT ON ALL LP RECORDS! than ever before possible. This unique 20. Turntables generally appear to Best 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. lE-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 the edge of the motorboard. FREE HI-FI CATALOG and Bargain audio dealer's. Price List. Chicago E lectronics. 420 E . 87th 21. Disc recorders also appear well St., Box 171, Chicago 19, 111. 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. lathe not driven from tnrntable center. Con­ the platen, and place the camera so that tact Box CM-3, Andio Engineering. 2439 fletcher Drive, Los Angeles 39, California the lathe makes an appreciable ancyle 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 IJP cartridge, new point, $32.50; Altec 602-A show-up best head-on, of course. Those 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! preamp. $55. Robert Ballum, 36 Wakefield with the camera directly in front of and Ave., Port Washington, N. Y. somewhat above the unit. Make sure HI-FI WILLIAMSON TYPE both reels are on the machine and that FOR SALE: Altec Lansing M-ll microphone AMPLIFIER systems (2) in perfect 'Condition; in use one the tape is properly threaded month. Consists of 21-B midget condenser KIT microphone, base, power supply, cable. $100 23 . Be careful of 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 en~

70 AUDIO ENGINEERING • MARCH, 1953 fastened to the picture, preferably by pasting on the back. Editors, alas, are PROFESSIONAL not mind readers. And don't ever use omEcroRY paper clips to hold together a number of photos. 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 some­ thing in reproduction, and sharpness in U. S. Recording Co. the original is very important. U2l V.Dllont Ave., Waahia,toa 5, D. c. Lincoln 3-2705 ••• David Sarser and his sister Sebe, still ap­ pearing under the guidance of impressario Maximilian Weil, president of Audak Com­ pany, repeated their New York Audio Fair s uccess at the West Coast F a ir . . . Debbie "EVERYTHING IN HIGH FIDELITY" Ishlon, director of public relations for Co­ From Primary Components lumbia Records, Inc., is assembling a to Completed Custom Audio Equ ipment brand new high-fidelity music systen1-the better to hear the fine records she pub­ licizes, no doubt . . . Another distaffer, Margaret Delano of Harper & Brothers, publishers, is plenty hep on a udio as a re­ sult of handling the editing assignment on KIE~tnd Corp. Edward Tatnall .Canby's new book-sched­ uled for March 18 publication . . . Les 820 West Olymp ic Blvd . • Los Angeles 15, Calif. Paul, Capitol Records star, is on verge of completing one of the country's most RIchmond 7-0271 ZEnith 0271 lavish recording s tudies, built as an addi­ tion to his New Jersey home-among its amenities are s uch a udio hors d'oeuvres as six Ampexes, one disc recorder, T elef)lnken microphones, etc . ... Bob Silverman, pro­ In Southern California it's gram director, station W ABF, busily pre­ paring a special a udio issue of the sta­ tion's monthly program-listing magazine HOLLYWOOD ELEaRONICS . . . Gil Demsky, Anton Schmitt, and (in The Audio Mile) Jimmy Carroll, custodians of H a rvey Radio Company sound depa rtment, a re Distributors ot Hi Fidelity initiating campaign for. improved br oad­ Components Exclusively cast q uality of New YOl'i( Philharmonic Webster 3-8208 and NBC Symphony concerts- a ll three have been recording the concerts off the 7460 Melrose Ave. Hollywood 46, Calif. air for years, a nd are unanimous in the r r $ opinion that a udio quality has deteriorated noticeab ly in recent months ... Michael von Mandel, American legal and sales rep­ resentative for Germany's T elefunken Company, off for t hree-week visit with ELECTRONIC company officials in E urope . .. 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 w hich destroyed portion of Cmnpco 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 ... F. Sumner Hall, president of Audio Equipment Sales, has perfected a new telephone plug to end all plugs-contains many unique a nd original features .. . Entire a udio fraternity well entertained and enlig htened at February meeting of AES in New York-featuring many of Announcing the opening of the the most prominent persona lities in t he BROOKLYN HIGH FIDELITY. SOUND CENTER a udio fie ld in a round-table discussion-on the platform were Wilfred B. Whalley, 2128 Caton Ave., Bklyn 26, N. Y. moderator, C. J. LeBel, Frank H. McIntosh, (Cor. Flatbush A ve . ) Jerry B. Minter, H. A. Pearson, Herman Tel: BUckminster 2 5 300 H. Scott, a nd Llewellyn Bates Keirn . . . Elton Nachman, formerly with Audio­ High Fidelity Components and Complete Systems Video Produc ts Corp. getting acclimated Write for Brochure to new position with Sun Radio & Elec­ tronics Corp.

WANTED: DIRECTOR OF ENGINEERING An outstanding oppo~tunity for an electronics engineer of executive caliber to head up the development program for a nationally known manufacturer in the electronics field. A smaller firm with two well-equipped plants and excellent laboratory facilities, particu­ larly in the audio and electro-acoustic fields, 70% of the company's business is civilian. Starting salary $12,000 with opportunity for increased earnings through bonus and advancement. Stock participation open. Appointee will be a member of small top manage­ ment group. QUALI FICATIONS: Must be a graduate engineer or physicist, preferably in com­ munications field. Age: 30-50. At least 8 years of engineering experience with some TAPE REELS. STORAGE CANS . AND SHIPPING CASES FOR EVERY PROFESSIONAL REQUIRE· supervisory activity. American citizenship and clearance for secret. Originality and creative MENT ALWAYS IN STOCK thinking essential plus ability to plan, organize, and coordinate the efforts of various JV'riu lor ,/tUriplivt liltra/llrt a"d prire list project groups. COMPCO CORPORATION J\laml /flclurt'rS 0/ (I,1t produc/$ lor the Audio. CONFIDENTIAL PERSONAL INTERVIEW may be arranged during IRE meeting in V imal industry. March in N.Y.C. Address reply stoting personal qualifications, including : education, em­ 2251 W. St. Paul Avt!. Chicago 47, Illinois ployment and earnings record, patents and inventions, publications, intefests, family status. ' Box DM-1, AUDIO ENGINEERING, p, O. Box 629, Mineola, N. Y. All replies treated in strict confidence. Our own staff knows of this advertisement.

AUDIO ENGINEERING • MARCH, 1953 71 YOU CAN NOW GET THE FAMOUS A 0 V E R T 1'5 I N G HARTLEY 215 SPEAKER SO EASilY IN 0 EX • AND IN THE UNIQUE "BOFFlE". Air Tone Sound & Recording Co .. . 69 Allied Radi , Corp...... 43 Altec Lansing Corp...... 53 Since our last advertisement we have been far from idle. Our factories 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 in a variety of finishes and styles, made from the finest American materials Bell Telephone Laboratories ..... 18 and workmanship. For extreme economy we have preserved the knock-down Brooklyn Hi-Fidelity Sound Center 7 1 kit of parts, easily assembled in an hour or two; yet although of much finer Brush Development Co...... 4 quality, than those we used to send from England, the price is actually less. Camera Equipment Co...... 57 Boffles are made from half-inch stock, the front panel being three­ Cannon Electric C0...... 10 quarter inch tough board; all joints are keyed and glued; polished or un­ Chicago Transformer Co...... 5 1 polished; veneered in oak, mahogany or walnut; also in unfinished pine, if Cinema Engineering Co...... 7 you need a truly inexpensive housing for insertion in an existing cabinet. Classified Ads ...... 70 And-for the finest possible results, regardless of expense, we intro­ Compco Corp...... 7 1 duce the double Boffle, which, with two 215's w'ired in simple series, will Concertone Recorders ...... 6 1 Diacoustic Laboratory ...... 59 give you for $200 a performance not to be equalled by any 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 u.sed 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 ...... 4 5 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 SP'EAKER $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 SINCLE DOUBLE Maurer, J. A. Inc ...... '. 35 Minnesota Mining & Mfg. Co. . 36, 37 Veneered in oak, mahogany or walnut, completely finished $75.00 $85.00 Olympic Electronics Supply Co. .. 70 do do do do unpolished $50.00 $55.00 do do do do kit of parts $40.00 $45.00 Orradio Industries ) nc ...... Cover 3 Unfinished pine (can be stained and polished or painted) $40.00 $45.00 Partridge Transformers, Ltd. . . .. 67 do do kit of parts $30.00 $35.00 Peerless Electrical Products Div. .. 14 Pickering & Co. , Inc...... 17 Pilot Radio Corp...... 48, 49 HARTLEY TONE-CONTROL PREAMPLIFIER $35.00 Precision Electronics, Inc...... 64 HARTLEY 20 WATT AMPLIFIER $135.00 Precision Film Laboratories ...... 12 Presto Recording Corp...... 39 Complete with tubes. Prestoseal Mfg. Corp...... 66 If you have not already asked to be put on our mailing list, send a postcard Professional Di rectory ...... 71 to London today, so that you can be kept fully informed on all our new ideas. Radio's Master ...... 52 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 A AST! no n.o,-e unscheduled • prograHl breaks! SOUNO-PlA TE AN ENTIRELY NEW MAGNETIC RECORDING TAPE

It~s break-proof•.. just what you~ve been wanting

(Produced and Sold Under the IRISH Label as 220RPA Red Band ORRadio Magnetic Tape)

Here, at last, the sum total of everything you have ever wanted in a professional magnetic recording tape. ORRadio IRISH 220RPA SOUND-PLATE eliminates your physical problems in magnetic tape recordings. It won't tear or break. It has all the excellent qualities that have made ORRadio IRISH 211RPA the most popular tape among professional engineers. Yes, SOUND-PLATE costs a little more . .. but, in the long run, it wi ll prove to be not only the most satisfactory, but the most economical magnetic recording tape you can use.

Try SOUND-PLATE at our expense! Buy a reel of SOUND-PLATE at your favorite Radio Parts Distributor. If you are not completely satisfied, return it to your distributor who has been authorized to refund your money.

1200 Ft. SOUND-PLATE on Plastic 2400 Ft. SOUNC·PLATE on Meta, Reel ...... •. $15.50 List Reel ...... •. $33.85

Manufactured In U.S.A. bv

ORRADIO INDUSTRIES, INC. OPELIKA, Jl7orld's Largest Exclusive Magnetic Tape Manufacturer ..... - /' ------~-- • - ~- • MINIATUR E AU D 10 UNITS ••. RCOF CASE • Type MIL Pri.lmp. Sec."" Imp. DCin Response Max. level List • No. Application Type Ohms Ohms Pri., MA ± 2db. (Cye.) dbm Pri.ce • H·t Mike, pickup, line to gn I TFlA10YY 50,200 CT, 500 CT ' 50.000 0 50·10.000 + 5 $16.50 • H·2 Mike to grid ·.. rlAllYY 82 135.000 50 250·8.000 +21 16.00 H·3 Single plate to s i n gl ~ grid TFlA15YY 15.000 60.000 0 50·10.COO +6 13.50 • H·4 Single plate to single grid. TFlA15YY 15.000 60 .000 4 200·10.000 +14 13.50 • DC In Pri. • H·5 Single plate to P.P. grids TFlA15YY 15.000 95.000 CT 0 50·10.000 +5 15.50 RCOF CASE H·6 Single plate to P.P. grids. TFlA15YY 15.000 95.000 split 4 200·10.000 +11 16.00 • DC in Pri. length .. ·...... 1 25 / 64 • H·7 Single or P.P. plates to lin,e TFlA13YY 20.000 CT 150/ 600 4 200·10.000 +21 16.50 Width ...... 61 / 64 H·8 Mixing and matching '- TFlA16YY 150/ 600 600 CT a ~0·1!l.000 +8 15.50 Height ...... 1 13/ 32 • H·9 82 / 41 :1 input to grid TFIAlOYY 150/ 600 1 meg. 0 200·3,000 (4db.) + 10 16.50 Mounting ...... :...... 11/ 8 • H·tD 10:1 single plate to single TFlAI 'jYY 10.000 1 meg. a 200·3,000 (4db.) + 10 15.00 Screws ...... 4 ·40 FI L. • grid Cutout ...... 7/ 8 Dia. • ~ Reactor TFlA20YY 300 Henries·O DC, 50 Henries·3 Ma. DC. 6.000 Ohms . 12.00 Un it ~ eight ...... 1.5 oz. • •

• • • COMPAC T AU D 10 UNITS .•. RC-50 CASE • Type MIL Pri.lmp. Sec. Imp. DC in Response Max. level List • No. Application Type Ohms Ohms Pri., MA ± 2db, (Cye.) dbm Price • 11;20 ' Single plate to 2 grids. can TFlA15YY 15.000 spiit 80.000 split 0 30·20,000 +12 $20.00 • ·also be use d for P.P. plates H·2t Single plate to P.P. grids. TFlA15YY 15,000 80.000 split 8 100·20.000 + 23 23.00 • DC in Pri. RC·50 CASE • H·22 Single plate to multiple line TFlA13YY 15,000 50 / 200. 8 50·20,000 +2'3 21.00 length ...... 1 5/ 8 • 125/ 500" Width ...... •...... 1 5/ 8 H·23 P.P. plates to multiple line TFlA13YY 30,000 split 50 / 200. 8 30·20.000 + 19 20 .00 Height ...... 2 5/ 16 • 125/ 500 " BAL H-24 Mouoting ...... 1 5/ 16 • Reactor TFlA20YY 450 Hys .·O DC. 250 Hys.·5 Ma. DC. 6000 ohms .. . 15.00 65 Hys.·10 Ma . DC. 1500 ohms. Screws ...... #6·32 • Cutout ...... 1 1/ 2 Dia . • Unit Weight ...... 8 oz. • • • • SUBMI NIA TURE AU D I 0 UNITS ... SM CASE • Type MIL Pri. Imp. Sec. Imp. DC in Response Max. level List • No. Application Type 'Ohms Ohms Pri., MA ± 2db. (eye.) dbm Price • H·30 Input to grid TFlA10YY 50 *** 62.500 0 150·10.000 +13 $13.00 H·3t Single plate to single grid. TFlA15YY 10.000 90.000 0 300·10.000 + 13 13.00 3:1 H·32 Sing le plate ,to line TFlA13YY 10.000···· SM CASE 200 3 300·10.000 + 13 13.00 H·33 . Single pl'ate to low TFlA13YY 30.000 50 1 300·10.000 + 15 13.00 Length ...... 11/ 16 Impedance Width ...... 1/2 H·34 Single plate to low {i'l'A13YY 100,000 60 .5 300·10,000 + 6 13.00 Height ...... 29/ 32 Impedance Screw •...... 4·40 FIl. H·35 Reactor TF1A20YY 100 Henries·O OC, 50 Henri es·1 Ma . DC, 4,400 ohm s. 11.00 Unit Weight ...... 8 oz.

• ~ The impedance ratings ore • 200 ohm termination can be used for 150 ohms or 250 ohms. 500 ohm termination can be used for 600 ohm s. listed in standard manner. • Obviously, a transformer with •• 200 ohm termination can be "sed 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 so, I' re impedances. with corresponding reduction in frequency range . With 200 ohm source ance can operate from a tube • secondary impedance becomes 250.000 ohms . .. loaded re sponse is -4 db . at 300 cycles. ' representing a source imped­ ····can be used for 500 ohm load ... 25'.000 o~m primary impedance , . • 1.5 Ma . DC. ance of 1700 ohms, etc. 1n addition, transformers can be vsed for applications differ­ ing considerably from those shown, keeping· in mind that impedance ratio is (ohstont. Lower sour-ce impedance will improve response and level ratings . . . higher source im­ pedance will reduce frequency ronge and level rating_