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a .4 AUGUST 4 1951 35c

ENGINEERING

lot/ce,Pe- 41-ee

,1 ' , Ì j I I , , Ill , , , ,, . , . . IN I I NÌ lit Here's the RECORD- MAKING COMBINATION

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Today's trend to high fidelity phonograph reproduction demands ... and you get the same higher quality than ever before -in both the original sound record- unsurpassed performance when you ings and the masters from which pressings are made. And the use Audiotape and Audiodiscs country's leading manufacturers of fine phonograph records have found that Audiotape and Audiodiscs are the ideal combination in your recording work for meeting these exacting requirements. There's nothing special about the Audio products Master Audiodiscs -the choice of record -makers for more than a used by the phonograph record industry. Except decade -are now used for the vast majority of all phonograph for size, Master Audiodiscs are exactly the same records produced in this country. That's because their outstanding as the Red Label Audiodiscs used anywhere else performance is a matter of record - known throughout the industry - with the same superior lacquer, applied by the for consistent uniform quality, freedom from humidity effects, and same precision coating process and meeting the exceptionally low surface noise at all diameters. same exacting standards of flawless perfection. Although magnetic recording is relatively new in the record -mak- And the Audiotape used in record making is identical which is available for ing field, Audiotape is already widely used for recording the original to that general use by all sound recordists. sound. Here, too, its preference is the result of proved performance. If it's quality you want, Audiodiscs and Audio - For professional recordists know that they can always depend on tape speak for themselves. Remember, too, that Audiotape for the finest in magnetic recording - with unequalled Audiotape, in both 1250 and 2500 foot uniformity and minimum distortion at maximum output. reels, is guaranteed splice -free! AUDIO DEVICES, Inc. 444 Madison Avenue, New York 22, N.Y. Export Dept.: 13 East 40th St., New York 16, N. Y., Cables "ARLAB" 'Trade .tlark Successor to pI Established 1917

C. G. McProud, Editor Ladd Haystead, Publisher Harrie K. Richardson, Associate Editor Luci Turner. Production Manager S. L. Cahn, Advertising Director Lucille Cart ,', Circulation Manager H. N. Reizes, Advertising Manager

Editorial Advisory Board Representatives H. Thorpe Covington, Special Representative Howard A. Corm 677 N. Michigan Ave., Chicago 11, III. Sanford R. Cowan, Mid -West Sales John D. Colvin 67 W. 44th St., New York 18. N. Y. James C. LeBel C. Galloway, Pacific Coast Sales J. 816 W. 5th St., Los Angeles 17, Calif. BOB HOPE J. P. Maxfielc Technical Book ti Magazine Co. 297 Swanston St., Melbourne, C. I. "Comedy Hour," NBC George M. Nleon Victoria, Australia

i CONTENTS AUGUST, 1951 Vol. 35, No. 8 In the act... Publisher's Letter . 2 Audio Patents-Richard H. Dorf 4 without hiding the star Letters 6 Editor's Report 10 Efficiency of Direct -Radiator Loudspeakers - Vincent Salmon 13 Two -Tap Bass and Treble Compensated Volume Control -William O. Brooks 15 RCA's Audio and the Armed Forces -Lt. George llfarakas, USN 16 Whodathunkit -2E was Born in California 17 Constant -Resistance Dividing Networks -Bob Hugh Smith 18 New Approach to Loudspeaker Damping -Warner Clements 20 tISTA#RMAK R" Acoustical Balance in Recording -Eddison von Ottenfeld 23 AUDIO engineering society SECTION ... a ribbon -pressure microphone that Toward a More Realistic Audio-Ross H. Snyder 24 is so slim ... so skillfully styled ... so The Pacific Electronic Exhibit -List of Exhibitors 28 unobtrusive ... you must look twice to Survey of European Sound Apparatus -John K. Hilliard 32 see it. Record Revue -Edward Tatnall Canby 34 New Literature 43 Despite its slim construction, the New Products 44 STARMAKER meets the exacting quality Book Reviews 51 standards of other RCA professional Schedule of Exhibit and Convention Events 56 Broadcast microphones. Pick -up is non - "The Representatives" of Radio Parts Manufacturers, Inc. 59 directional. Frequency response is sub- West Coast Jobbers List 61 stantially uniform, 50 to 15,000 cps. It Employment Register 62 is free from wind rumble and air blast Industry Notes 62 ... and virtually impervious to me- Industry People 63 chanical shock. Advertising Index 64 The STARMAKER fits any standard COVER microphone stand ... can be used in microphone. No The majestic Bay Bridge extending from San Francisco eastwards toward Oakland place of and RCA and Berkeley, with Yerba Buena Island approximately midway between the two extra attachments needed. ends of the bridge. With the exception of the renowned cable cars, the For delivery information call your Bay Bridge and the shorter Golden Gate Bridge are the most RCA Broadcast Sales Engineer, or write: famous attractions of the metropolis which plays host Department TT -7, RCA Engineering to the Pacific Electronic Exhibit this month. Products, Camden, N. J. (In Canada 'Both Editor and Publisher are aware that this photo is receraed. Artistic license has been invoked to make a more photogenic cover I write: RCA Victor Limited, Montreal.)

RADIO MAGAZINES, INC., 342 MADISON AVE., NEW YORK 17, N. Y.

Á1010 ENGINEERING (tille registered U. S. Pat. OR.) is published monthly at 10 McGovern Ave., Lancaster, Pa., by Radio Magazines, Inc., D. S. Potts, President; Henry A. Schober, Secretary -Treasurer. Executive and Editorial & res: 342 Madison Avenue, New York 17, N. Y. Subscription rates -United States, I'. S. Possessions and Canada, $3.00 for 1 year, $5.00 for 2 years: elsewhere $4.00 per year. Single copies 35c. Printed in U. S. A. All rights reserved. Entire contenta copyright 1050 by Radio Magasines, Inc. Entered as Second Ciao Matter Fehnury 9, 1950 at the Post (Mire, Lancaster, Pa. under the Act of March 3. 1879. RADIO CORPORATION AUDIO ENGINEERING AUGUST, 1951 of AMERICA Pedeedeteir:d 4etee'i

JUAN RODRIGUEZ CABRILLO first saw the cent of all defense dollars will be spent in the field Pacific Coast in 1542. In the 409 years that fol- of electronics. lowed you would expect some changes to have In our sister field, video engineering, the Coast is come about in this region- though hardly enough also making spectacular strides. The entertain- to justify a special issue of a technical magazine. ment news is dominated these days by reports of the Yet the events of the past decade, unprecedented in marriage of TV and the movies. The reports of new any other area or in all history, are so fantastic, so production units run into hundreds. The Coast widespread in their industrial and commercial ef- has its own TV hook -up, and the relay network to fects on all fields including electronics and its voice, connect East and West is now promised to be ready audio, that recognition becomes mandatory. for use within a few months. When over five million people pulled up stakes A dynamic manifestation of all this activity is the and marched across the nation it became the great- annual Pacific Electronic Exhibit to be held this est mass migration in history. Of course, a war was year in the Civic Auditorium, August 22 -24, at San its motivating factor, so when the war was over Francisco. The affair will attract something over you would expect the people to have drifted back 7500 people actively engaged in the manufacture to their former homes. They didn't. Instead, they and sale of professional and commercial electronic not only stayed but others came out to join them. products. This year 70 Eastern and 50 Western And they are still coming. In California, during the factories are exhibiting, plus 19 manufacturers' last decade, the population increased 53.3 per cent. representatives and seven university and govern- Such an increase would indicate commerce and ment agencies. industry must be moving too. It has. We find great The displays are not open to the general public. national organizations moving their headquarters But those interested besides WCEMA and IRE mem- westward. We find branches of eastern factories as bers may secure tickets without charge by proper large as their parents burgeoning almost everyplace. identification in the lobby during the opening hours. Civilian employment in the Golden State went from San Francisco, where the exhibit is being held, two and a half million in 1940 to four and a half can proudly boast that it has been called "the million in 1950. Retail sales went from three to youngest of the world's truly cosmopolitan cities." eleven billions in the same period. Since 1940 the "Metropolitan District" of 3,314 Steel, ships, and styles now move from the Coast square miles has had the greatest population growth all over the world. And, from Boeing at Seattle to an of any corresponding area in the United States- empire of wings in Southern California, the aviation approximately 40 per cent or 583,000 souls. industry has made this area a favored spot. Visitors to the exhibit will be amused at the cable Where there is a concentration of aviation you cars, thrill to the Golden Gate and the mighty expect to find strong electronics representation. bridges (see Cover), enjoy the bracing air, dine on Where there is a mass growth of population you ex- some of the best food of the widest variety to be pect to find communications in full growth. And found in the nation. naturally the voice of both, audio, must also be in So to the Host City, the several thousand lE sub- crescendo. scribers in the West, the West Coast Electronic Let's look at the facts. Quoting from the Economic Manufacturers' Association, and audio folks every- Survey of Calif ornia-"Manuf acture of electrical where, a salute in the form of this special issue. machinery and equipment in California showed the Although it is off the beaten track (and for the largest expansion between 1939 and 1947 of any regulars who protest any change of format in their large industry group. Some 216 new establishments favorite technical magazine we promise to return were added, the number of workers increased by to orthodoxy next month) we hope it will be re- 264 per cent or more than three and a half times, ceived as a job that was deserved by this new, and the value added by manufacture increased by spirited, little giant segment of electronics. 515 per cent." During 1950 employment increased In the language of the California dons "Bien another 25 per cent over 1947 levels. Venido." Now comes a report that over a billion dollars worth of contracts for electronic equipment is in the process of being let by the aircraft industry alone. The West Coast Electronic Manufacturers' LaddA(a7so.c.e Association says that between ten and twelve per

2 AUDIO ENGINEERING AUGUST, 1951 Engineering Data .. on ARNOLD TAPE-WOUND CORES . . " ' n ° °...... ;: ...... ;...... '/...... rn , ..: . ::::.r11;;;i:...... :i .i ://11// 1nn . . i.1../c::'...... ,\.1..1...:::, rn ...... 1/ . /r/.. :n.ïi//.,:::/ 11;:n ;::r11.1.1 / . ï :N1 . ./n ///1 n/ ; 1;,. . /11;::. :1.r.111 :N ,1. 1 11 .r1 1 /,1::j1.,11 /1/_11:000001101010111010111000101100010001011 .11!i¡iG/11/ r11.. ,11/::; 11.r1../. 1r1r1,. i ;0.1/ .0,r;111r1 ;ï,11/.//::1 : .1,1.; 0.\\ /.1...1°1-4//..,, 1.1 11/ u n,e ' n;// 1,. ; 11/ , i:: : /. :i..:u¡:1. .d¡ ::::::::: n :;:::::¡11,r11. ::: 1 ,1 u 1 ¡ /n ,. ,..11.1r/ ::.n..,0 : ::ï ::i . %an:%, , %i::;: :: :::1. !,./,./¡;ï:::::N S 1 : :%', !../_...r;. .1! ..1/ N ./E p Í1 i: i,1r/r : r. :$1` ¡ 5:';;111.",//11Ç Ç _ :1;::t`;%0,0 C;; ,,11¡:10001100110010110110001110010110011000000110111:¡::::' \1.0;;,,, w1:: ; 11r i :::r:ñ¡ :.,,,:111000110011211' 1111 : ! ,.1. 1::: 1r1::;Y 1..0.11/1. 11.;0,/1.. r1.1,1,.//...... S AUA% _:/. A . LL .1.::: RM 1 .. ; 1 . 9 ./; ;: ../ / ...... ;ï\.11111. 1 .....;...... 1::1/r1/

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ir worerE Fo, e WO' Ca,' AUDIO ENGINEERING AUGUST, 1951 3 RER -O -KUT Specialists in Sound Equipment for Broad- casting and Public Use! The World's Finest!

THE

Professional 131/4 DISC RECORDER for Standard RICHARD H. DORF and Micro -Groove ELECTRONIC MUSICAL INSTRUMENTS must Recording There are definite advantages to this ar- have provisions for vibrato or tremolo, rangement. Many instruments employ a preferably the former. When vacuum modulator tube (usually a reactance mod- tubes are used for tone generation vibrato ulator or one kind or another) with each is always possible, simply by injecting a oscillator tube; this circuit does the whole vibrato -frequency (4 to 7 -cps) signal some- job in a single pentode. More important is where into the generator to vary its fre- the frequency stability. An electron -coupled quency. It stands to reason, however, that INSTRUMENTS IN ONE -ordinarily, at least -an oscillator whose 1. A Professional Recorder frequency can be varied that easily cannot 2. A High -Fidelity Phonograph be very stable. The same problem arises in 3. A High -Fidelity P.A. System FM transmitters which employ a reactance tube to produce the modulation. The Challenger, America's finest 131/4 Disc Recorder, Is built to meet the respective needs of the professional James A. Oswald of Chicago has pat- recordist, musician, educator and recording enthusiast ented a vibrato system which does not who wants to make permanent, professional recordings. Embodies the most advanced design, engineering and greatly affect the stability of the tone gen- production techniques in the disc recording Industry. erator, in Patent No. 2,506,679, assigned The Challenger's many exclusive operating features to Central simplify and improve the art of disc recording. NOTE: Commercial Company, maker of Tape recording enthusiasts need the "Challenger" to the Lowrey Organo. re-record their finished tape after it has been edited ... input jack available, no special attachments required. RECORDS disc from 6" to 131/4" masters. PLAYS back disc from 6" to 16" transcriptions, standard or micro -groove. With heavy duty synchronous motor $439.95

CONTINUOUSLY VARIABLE - Fig. 2 SPEED TURNTABLE OF BROADCAST QUALITY oscillator is normally stabilized by the fact that with correct selection of component Plays at ANY speed from 25 to 100 R.P.M without distor- values, changes in electrode voltages cancel tion. Ideal for record collec- each other. This process still goes on in tors, musicians, singers, disc jockeys, music schools, dance the circuit of Fig. 1, the only additional I general schools, provision being a periodic change of plate broadcast studios, etc., wher- Fig. 1 ever controlling pitch and current, which does not affect stabilization. tempo Is required. Figure 2 shows the vibrato -frequency os- The circuit appears in Fig. 1, with a set Model CVS -12, (illustrated) cillator illustrated by the inventor. It is chassis, motor and turn- of sample component values. This is one table, assembly not particularly new, being a more or less $84.95 net of the master oscillators used in a gener- standard phase -shift oscillator with a fol- Model CVS -12P, mounted in ator system which includes twelve of them, portable case with 16" lowing amplifier. The exact values, how- dual stylus pick -up $124.95 net each followed by a string of frequency di- viders to produce the lower octaves. The ever, should be of interest to many elec- * * * * * * 6SK7 is connected as an electron -coupled tronic music enthusiasts to save them the oscillator with its cathode, grid, and screen trouble of designing the oscillator. On this same subject, a different kind of MODEL LP -743 forming the oscillator triode. An electron - coupled vibrato- frequency oscillator is the subject 3 -SPEED 12 INCH oscillator is effectively a combined oscillator and isolating amplifier, and here of Patent No. 2,546,645, which the inventor, TRANSCRIPTION the amplifier is made up of the screen Thomas H. Long, has assigned to C. G. TURNTABLE (acting as cathode), the suppressor, and Conn, Ltd., maker of the Connsonata. Mr. the plate. The suppressor, which is Long's oscillator is diagrammed in Fig. 3, Recommended by leading the and those familiar sound critics. Induction control grid of the amplifier triode, is con- with the Connsonata type motor, designed for nected to a source of vibrato -frequency os- will notice a marked similarity to the os- smooth, quiet, vibration - cillations. cillators used as tone generators in that free operation. Instantane- instrument. Mr. Long has ous speed changes 78 result, apparently been - As a the gain of the amplifier tri- experimenting 45 and 33Sh - without ode varies at the rate of around 6 cps. This for a long time with this stopping turntable or re- kind of oscillator, for he has a number of $54.95 net. moving disc. means that the transfer of oscillator-fre- patents quency energy through capacitor C back on variations of it. The circuit is essentially a modified See ... hear ...compare REK -O to the tank circuit also varies at the vibrato -KUT products at lead- Hartley. The is ing music stores, audio-visual dealers and radio parts rate. The result is a periodic change in plate connected to one jobbers... or write for literature. output frequency, accompanied by a small side of a tank circuit, the inductor of which as well. is the primary of a transformer. Output is amount of amplitude variation The taken from the two combine to produce a pleasing vibrato secondary, across a po- effect. tentiometer. The other side of the tank is 38-01 Queens Boulevard not connected directly to the grid but goes instead through potentiometer R,. The Long Island City 1, N. Y. Audio Consultant, 255 West 8-ftlr Street, New York 24, N. Y. [Continued on page 48]

4 AUDIO ENGINEERING AUGUST, 1951 SYMBOL OF SUPERIOR SOUND SINCE 1934

flEELY EnTERPRISES REPRESENTATIVES FOR AMERICA'S ,S FINEST SOUND REPRODUCING EQUIPMENT ay-wee-Aid B 411) TAPE RECORDERS 0 M I C R O P H O N E S 0

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WE'll BE IN SPACE 709 -710 of the 7th Annual Pacific Electronic Exhibit. VisitOurioundDemons ration During the Exhibit ug. 22- 23 -24. Hotel Wh)comb, Second F nor. .Ri nE ? ES LOS ANGELES SAN FRANCISCO SACRAMENTO ALBUQUERQUE 7422 Melrose Ave. 2830 Geary Bird. 309 Ochsner Bldg. 107 5. Washington St. Los Angeles 46, Calif an Francisco 18, Calif. Sacramento 14, Calif. Albuquerque, New Mexico Also Representing HE T- PACKARD COMPANY - Booths, 711_ -712 FOREMOST MANUFACTURERS iOFf INSTRUMENTATION FOR COMPLETE AUDIO

AUDIO ENGINEERING AUGUST, 1951 5 Here's why those in the know LETTERS - demand Editor vs. Canby vs. B.B.C. Sir: Will some audio engineer shed a tear for the perplexed non- technical reader? CANNON The EDITOR'S REPORT (1E, June, 1951) on Loudness vs. Frequency Content con- cludes that, "If the monitoring were done PLUGS principally by listening to the monitor speaker rather than by adjusting the level to satisfy the VU meter, it seems this trouble would not exist at all if the speaker were sufficiently good. . The following month Canby, wiping the Here's another example of the meticulous blood from his unbowed head with that care Cannon Electric uses in building con- Damp Cloth, staggers from the control room in nectors for highly specialized, tough jobs. firm the conviction that be it ever so humble, there's no place like the old This AN -"M" type connector is moisture - familiar home listening spot. proof, vibration -proof and pressurized. Ra- But perhaps we should be thankful for dio shielding is provided and every threaded small mercies ; our transatlantic cousins part is drilled for safety wiring. have an added problem. Somerville and Brownless (Listeners' Sound Level Pref- No corners are cut nothing is over- erences- B.B.C. Quarterly. January, 1949) looked to assure you outstanding perform- report a "striking divergence" between the ance. This connector is designed for aircraft men and women program engineers of the use but there are more than 18,000 different B.B.C. when listening to speech. The level Cannon Plugs made with the same care to preferred by the men being seven db greater serve the exacting needs of many industries. than that preferred by the women. One is reluctant to inject the romantic If you are looking for real value, regardless note in a technical magazine, but surely of the field you work in, your best bet is there is something to be said in favor of less Cannon. wear and tear on the listener's gain control. Engineering bulletins describing each B. Mitchell, of the many basic types of connectors are 225 Foster Ave., Brooklyn 30, N. Y. available. We will gladly send you any of Audio Colleges these if you will simply describe your con- Sir: nector requirements. I have just received the July issue of - and noticed your editorial about College Audio Training. While Michigan State does not at offer a course in Audio En- Molded Polychloreprene inserts 75- present 80 shore hardness provide pressure - gineering, I have had such a course added proofing of both pin and socket con- to our catalog for next year. As planned, it tacts. Have high dielectric strength under wide range of temperatures will he a three- hour-per -week elective and at extreme altitudes. Mated fit- course for seniors majoring in electronics tings will not show more than 10 or communications. It will be taught for microamperes dielectric leakage and will not arc when subjected to 7500v only one term. dc at room temperature. I realize that the time allotted is too short to do the field justice but feel that it Pin Contacts machined from solid is a beginning upon which we may build in brass, silver -plated. Solder cup hand - tinned. the future. I. O. Ebert, Machined ball -in -cone joints provide radio shielding and improve vibra- Assistant Professor tion resistance. Michigan State College, East Lansing, Michigan. Socket contacts machined from solid Diamond vs. Sapphire copper alloy with new Cannon design, silver -plated. Sir: Matching serrations in end bell and Any further controversy over the relative shell make practical wrench -tighten- merits of sapphire vs. diamond styli may ing from one side of the installation seem old hat to most readers and about as without putting strain on contacts or wires. necessary as an argument over whether push -pull operation is better than single - Polychloreprene grommets make ended operation. moisture-proof seal over soldered con - nections. Engineers know that in every respect - except in the matter of initial cost -the Concentric rubber bushings under has the pressure of cable clamp provide diamond stylus advantage over its snug, moisture-proof wire entry. less precious counterpart. Diamond is a Eliminate usual strain on outer wires. harder, denser material than sapphire and Provision is made for grounding lug. can be given just as high a polish, if not higher. Whatever the polishing susceptibil- ities of natural sapphire may be, it should be recognized that practically all sapphire CANNON needles today are made of synthetic sapphire. Hckever high the polish may be originally, a relatively few hours of playing ELECTRIC time will suffice to grind two flats on the Since 1915 tip surfaces which are in contact with the grooves, and these flats have ever -increasing Cannon Electric Company magnitude as playing continues. The groove Los Angeles 31, California walls are in turn abraded by the sharp edges of these self -same flats. Factories in Los Angeles, Toronto, New "Phono Facts" in .E (June 1951) lists, Haven. Representation in principal cities. [Continued on page 50]

6 AUDIO ENGINEERING AUGUST, 1951 rc. " - y{ , tT Yf ri t Yt; ~ *USN jt s}' K r Yi ïi lit K .i uc u u ... U. !!r! i [..ÿ y`j.S; /T¡.¡ '_- ._>f1 . 1 tiL T. . c ,, ,. ¡yL s_s_{1_.' 1ìJ! ___L-° ' V_O tl .,, .,..,, - 4, nlX t

PRESTO selected for "The biggest job of radio journalism ever undertaken in the United Kingdom"

KENNETH MELVIN, New Zealand's No. 1 radio personality tours three continents with his PT-900. wherever you go there's PRESTO

From a Hindu temple in Singapore to the dank tomb "whether any tape- recording equipment has ever been of King Tut in Egypt ... from the imposing balcony of subjected to so grueling a test as my PT -900 ... not on a single Mussolini's palace in Rome to the historic tower of Big Ben occasion -over four months of constant operation, of in London. Kenneth Melvin has taken his PRESTO tape averaging six hours a day, under murderous variations recorder ... recording strange voices, sounds, music, that temperature, current, voltage and with constant man-handling have become living commentaries on people's from car to scene, upstairs and down cellars - customs, habits and surroundings. As official reporter not once has it failed me." for the British Festival, he is now travelling Every day, thousands of PRESTO owners are discovering, throughout the British Isles recording material just as Mr. Melvin did, that PRESTO equipment is made to for a 52 -week series of network broadcasts. give the utmost in performance and dependability. That's why "I shall be interested to discover ", says Kenneth Melvin, ... wherever you go there's PRESTO.

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4 Centering adjustment for h -f cone

5 Centering adjustment for 1 -f cone

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9 N -f cone. Diaphragm diameter only 2'ßs ". Wide-angle distribution to 15,000 cycles ':i:-: :v::::::\i:` ...... ;,' 10 Ample gap clearances

11 Massive 15" 1 -f cone. Bass response 35 to 2000 cycles at all volume levels

12 Cone rim treated to minimize edge reflections for smoother response LC-1A Loudspeaker Mecha MI -11411 13 Offset mount eliminates front cavity =Pi - insures smooth response MIP ...... nrexf ftp perfccf!

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A mong the great achievements of the RCA Princeton Laboratories is the development of the most advanced speaker in the world -the RCA Duo-Cone, Type LC -1A. Housing for LC-1A Expressly designed to give sound its true New Wall -Ceiling translation, this professional speaker is Ideal for sound reinforcement in con- executive offices. Port provided for trol rooms, auditioning booths, hall- increasing bass response. Finished matched by no other high -quality sound ways, talkback positions, elevators, in harmonizing 2 -tone umber gray. reproducer. Unique duo -cone design (originated by Dr. H. F. Olson of RCA Princeton Labs) It's Easy to mount provides a smooth response from 50 to The Wall -Ceiling Housing can be 15,000 cycles - with no resonant peaks, mounted for long or short "throws" harmonics, or transient distortion. Full -makes the wall and ceiling a part of the acoustical system. power is radiated over 120- degrees at 15,000 cycles -makes it possible to enjoy high - fidelity sound any place in the room! Smooth crossover response around 2000 cycles eliminates all undesirable interfer- ence between the high-frequency unit and The LC-1A the low- frequency unit. Controllable "roll - Monitoring Speaker, off" at 5 and 10 kc...when used with the with Console cabinet and MI -11707 filter... restricts the h -f distortion MI -11707 filter and surface noises present in many record- The finest reproducer in the business. ings. Available in a choice of 2 -tone Today, more than 3000 of these speakers umber gray or walnut finish. are serving in station control rooms, listening rooms, auditioning booths, lobbies, clients' offices, and private homes. For more information, mail the coupon.

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Address

1 City State 1 EDITOR'S REPORT

WESTWARD HO! -although even in the first place the hum from the amplifier was within specified limits. It developed that the WEST COAST FOLKS usually dislike, or just down- customer was using a speaker and cabinet combination right hate, anything written about them by an which was strongly resonant at 60 cps, with the result Easterner or by an Eastern publication. They that he heard hum which was all out of proportion to take their pen in hand and write nasty letters- to -the- that coming from the amplifier. editor, the general tone of which is "If you'd just get Such a condition is not unusual. In the search for out of your Ivory Tower and come out here to see for more bass, it is common practice to employ vented cabi- yourself, you'd know how wrong you are." Often their nets which can be resonated at 60 cps just as easily as at criticism is justified. But for this issue and this one some lower frequency-in fact, if the cabinet is not quite magazine, we'd like the westerners to know that at least large enough, it is likely to be easier to resonate it at two of the staff are West Coasters -the editor (Calif. the hum frequency. Inst. of Tech.), and whilom publisher Ladd Haystead Standing waves at the hum frequency are occasion- (U. C. L. A.). Also, we boast on the staff a Texican, ally encountered, and it is not unusual to find spots in a Sooner, and several-you should forgive it -New the listening room where the hum will be unbearable, Yorkers. while over most of the room it is not noticeable. Before The mention of the publisher reminds us that a few throwing out an amplifier as having too much hum, it is curious readers have wondered why the somewhat odd a good idea to make sure that neither the cabinet nor name of Ladd Haystead floats in and out of our mast- the room resonates at 60 cps-if that is the supply fre- head. What place does he have in the audio industry? quency used in your city. Answer : He has an interest in the magazine, candidly admits he knows little or nothing about electronics, and STEREOPHONIC BROADCASTING has thirty years of publishing work behind him. For One reader, Milton Sackin, writes to suggest the use reasons one and three we endure him. of two channels of transmission to provide stereophonic His advent in the office at spasmodic intervals usually sound in the home. These two channels could readily results in complete confusion -and sometimes in such be transmitted over the stations which have both AM things as this California-West Coast issue -1E's first and FM facilities, and listeners with two receivers and special. The staff's only hope is that he will not demand two speakers could then receive sound which should be a nude on the cover. more realistic than that from a single channel. The foregoing sentence elicited the following intra- While the idea is not new- having been tried in Hol- office correspondence : land some years ago -we admit to having attempted to LH to McP: Great idea. When do we do it? "sell' the idea to one of New York stations with both McP to LH : We don't! outlets. Station agreed, program producer demurred. See what we mean? On the same subject -what is wrong with this idea? Seriously, however, we will be at the Exhibit in San Two separate channels, fed by suitably spaced micro- Francisco -Booth 623-and hope we may have an op- phones, are used to modulate the positive and negative portunity to renew some of our West Coast acquaint- halves, respectively, of an AM carrier. Ordinary receiv- ances. ers using half -wave diode detectors would reproduce the output of one channel or the other, but since the AES STANDARD PLAYBACK CURVE microphones are reasonably close together there should The standard curve for record playback systems as not be much difference in the resulting sound. Stereo promulgated by the Society is beginning to be recog- receivers would have two half -wave detectors, of oppo- nized by equipment manufacturers, as evidenced by the site polarity, followed by separate audio and speaker announcement of the new Altec Lansing A433A Pre- systems. Thus no changes would be required in existing amplifier which incorporates this curve on one position sets unless a listener wanted the additional advantage of the equalizer switch. This is the second commercially of stereo reproduction. built unit made to fit the new curve -Pickering's Model One of the precepts of good engineering is that no 132E Record Compensator being the first. equipment should be obsoleted by a change of standards. In view of recent color TV decisions, it appears that all HUM VAGARIES standard -making agencies are not in agreement with One manufacturer of our acquaintance reports having this precept. We would, however, like to hear some ex- serviced an amplifier four separate times to reduce hum perimental work on a dual -channel transmission.

10 AUDIO ENGINEERING AUGUST, 1951 A new model of ritain's best audio amplifier, w t. compensated settings for I recordings LEAK "OINT ONE"

Distortion: TWO INTERCHANGEABLE 0.1% SPINDLES WEIGHTED TURNTABLE - HEAAVY MOTOR NO ASKS No r,ve, the features Leak "Point One" provides the ultimate in clarity and frequency response. Certi- PUSHER TYPE PLATFORM fied tests by British Nat'l that bring Physical Lab. (equiv. U. S. Bureau of Standards) prove SIMPLE 3 SPEED SETTINGS this triple loop power ampli. fier and pre -amplifier exceed manufacturer's performance fine claims. In the TL /12 amplifier, hum and noise levels fall within music -80 db and -72 db relative to 10 watts and are entirely inaudible. Feedback is taken AUTOMATIC STOP from low side of output home at end of last record transformer and due to the magnitude of feedback, there can be no rise of voltage. The reproduction of transients, especially of low frequency, is astonishingly clarified. At your dealer or write to BRITISH INDUSTRIES CORP. 164 Duane St., New York 13, N. Y. J GARRARD THE WORLD'S FINEST RECORD CHANGER Thë'WHY"and"HOW" OF GOOD SOUND IN YOUR HOME by G. A. BRIGGS Renowned authority

(LOUDSPEAKERS\

-19"-- -, $1.25

Speakers, baffles, acoustics, frequency response, etc.

SOUND REPRODUCTION II$2.25

Records, pick -ups, recording systems, design, etc.

NON -TECHNICAL SIMPLE LANGUAGE Easily, inexpensively installed Practical! Informative! in your present set. The only such books written expressly for the layman. Simple, Write for FREE FACT SHEET - language and easy -to- understand look when purchasing diagrams on principles important what to for for every home audio system. At a 3 speed record changer. your jobber or send check or money order. GARRARD SALES CORP. Dept AE5 BRITISH INDUSTRIES CORP. 164 Duane St., New York 13, N.Y. 164 Duane Street, New York 13, N. Y.

AUDIO ENGINEERING AUGUST, 1951 11 #4\e e4*. \ \

DIAPHRAGM MEMBRANE

AIR MAGNET GAP

POLE PIECE

More naturally than ever, your voice comes to gives more of the higher tones which add that the ear that listens through the latest telephone personal touch to your voice. receiver developed at Bell Telephone Labora- To work the new receiver, telephone lines tories. The reason: a new kind of diaphragm, need deliver only one -third as much power. So a stiff but light plastic. Driven from its edge finer wires can do the job. This is another new by a magnetic -metal ring, the diaphragm moves and important example of the way scientists like a piston, producing sound over all of its at Bell Telephone Laboratories work to keep area. Effective as are earlier diaphragms of down the cost of telephone service, while the magnetic -alloy sheet, the new one is better, quality goes up.

BELL TELEPHONE LABORATORIES

WORKI °IG CONTINUALLY TO KEEP YOUR TELEPHONE SERVICE ONE OF TODAY'S GREATEST VALUES Efficiency of Direct -Radiator Loudspeakers

VINCENT SALMON

An analysis of the factors affecting the efficiency of the type of speaker most commonly employed in sound reproduction installations.

put should correspond to what the ear hears. Since for indoor use the total 2 3 4 5 acoustic power radiated plus room Fig. 1. Characteristic effects determines the sound pressure at frequency regions in rather PRESSURE the free -space axial the ear, we choose power radiated LEVEL sound pressure re- than the axial sound pressure (which sponse of mass -con- serves for outdoor listening). As a Resoronce Piston Edge E trolled direct- radiator measure of electrical input the most Ronge Rise Hole speaker in infinite suitable for the present purpose is that baffle. power which the representative test FREQUENCY amplifier used will deliver to its rated load. Note that this is not the power to a matched load (one equal to source TIIE MOST WIDELY USED loudspeaker long. Waves in the cone material are re- impedance), since amplifiers are not is the direct- radiator, moving -coil, flected from the outer termination and operated that way. This rated load is mass -controlled type. In this note are arrive back at the voice coil so as to simply that given by the number on the discussed some of the factors influencing lower the mechanical driving -point im- output terminals : if they are marked its available -power efficiency, and espe- pedance, thus increasing the velocity 16 ohms and the amplifier is adjusted cially that in the piston- range. and hence the energy radiated. With in- In any speaker the response is com- increasing frequency, the half -wave monly understood to be the acoustic out- condition is next approached, and in put as a function of frequency for some region 4 the resulting edge hole is seen, constant electrical input. On the other arising from the high impedance re- hand, the efficiency is usually a single flected into the voice coil from the cone value, a sort of figure of merit, so that edge. Beyond this region the wave pat- the speaker may be compared with tern in the cone becomes more compli- others. As may be expected, there are cated, the driving -point impedance fluctuates many types of efficiencies, depending on considerably, and the speaker becomes more directional. All of which combination of electrical input, F.g. 2. Equivalent piston -range these add up to the ragged, bulged re- circuit of acoustical output, or test signal is used. speaker with amplifier connected. See text for sponse of region 5, that of cone vibration symbols. For the purposes of this discussion, in parts. Only in region 2 is there any- we shall consider the efficiency that is thing approaching a level response; in for one watt into a 16 -ohm load, the related to the program energy output of addition, the program energy the speaker a speaker used indoors. Thus the must power available to the speaker (not handle is greatest in this range, power available from the source) is said measure of acoustic output is the total about 50 per cent lying between 200 radiated power, and especially that near to be one watt. It is necessary to use this and 600 cps. criterion, since the maximum power 400 cps, where the program energy In this region a number of phenomena peaks. Consider next where this fre- from the amplifier is of no use to us: it cooperate nicely to simplify the an- is the maximum "undistorted" power quency region lies with respect to those alytical treatment. First, the cone is observed on a pressure- response curve. delivered to the optimum load that is moving practically as a rigid piston in useful. The speaker efficiency on this If the free -space axial sound pressure an infinite baffle ; hence the Rayleigh direct speaker in basis is then the number which when response of a -radiator radiation impedance may be used. Also by because it is a multiplied the power available to the an infinite baffle (chosen in the piston range the mechanical speaker gives (as closely as possible) reproducible mounting) is taken as a driving -point impedance is principally mass, the acoustic power from the speaker, function of frequency, it is found that that of a since the speaker is under the infinite -baffle condition. In the there are at least five regions of interest, working well above the fundamental frequency range considered, a cabinet starting at the low -frequency end. As resonance and well below vibration in will give a somewhat rougher response, shown considerably smoothed in Fig. 1, parts. Third, the speaker is not yet too fluctuating about that of the baffle. the first is centered about the funda- directional, so that the sound pressure mental resonance of the speaker. At very varies little with angle, permitting the Electromechanical Circuit response rises 12 total radiation to be calculated quite low frequencies the In the frequency range considered, db /octave, shows a peak at resonance simply from the sound pressure. Fourth. falls for most speakers the frequency is still usually 200 to 600 cps for 8- to 15 -in. (for the usual speaker), and then speakers, the output (source) impedance off. In region 2 the response is practi- moderate so that the (series) radiation resistance varies as the square of the of most satisfactory amplifiers may be cally constant; this is the piston range considered to be a constant resistance. where we shall calculate the efficiency. frequency. And finally, in this frequency range the inductance of the voice coil With this assumption, plus the others The program energy spectrum usually obtaining in the piston range, the equiva- maximizes in this range. In region 3 may be neglected. All this makes possible a simple expression for the piston- lent electromechanical circuit will be as the response peaks at the edge rise, in Fig. 2, where the force -voltage where the cone is about a quarter wave range efficiency. Efficiency is expressed as a ratio of analogy is used. Here E, and R, are * Stanford Research Institute, Stanford, acoustic output to electrical input. To the source open-circuit voltage and im- California. be useful, the measure of acoustic out- pedance, respectively; R, is the d.c.

AUDIO ENGINEERING AUGUST, 1951 13 Now we can begin to introduce the eter in inches. A good approximation to piston -range approximations. In prac- d is the distancè from the top of the in- tically all direct -radiator speakers, the nermost bead on the annulus to the op- last denominator term in the first posite outer clamp diameter of the cone. brackets can be neglected, because of See Fig. 5. the low efficiency. Since the speaker is mass controlled, the first denominator Analysis of Formula terni in the last brackets can be neglected, and since the frequency is not too Let us now examine this expression Fig. 3. Measurement of power available o more high. rr = 5.6 x 10- *. closely. The effect of frequency amplifier load. 'f'd For most properly used direct- radiator speakers R, /R1 has canceled out because of the two main assumptions that the principal is near 0.85. Finally, let us examine the resistance of the speaker in ohms; BI mechanical-impedance component is that is the product of flux density in gauss of the moving mass, and that the radiation resistance varies as and conductor length in cm ; m is the Cone the square of total moving mass, including the speaker the frequency. Two important factors mass m, and the radiation mass mr= in the efficiency are seen to be the space 6.6 x 10-3d' (mr is in grams, d is ef- factor and gap energy. In the form given, the influence of magnet size is fective cone diameter in inches) ; and easily seen, for magnets the series radiation resistance is given are character- ized by a guaranteed maximum ex- by r,.= 5.6 x 10 -ef'd+ in mechanical ohms. Top Core ternally available energy. In a well where f is the frequency in cps. If Plate de- the signed PM speaker, about 40 per cent r.m.s. cone velocity is y (in cm. /sec.), of this energy apears in the useful gap, then the radiated acoustic power in watts the is Pa= 10-7s4r,.. remainder being lost in leakage and fringing. Thus efficiency may be The power available to is in- the load creased by using larger magnets obtained by replacing the speaker by only as long as iron saturation is not a RI, the rated load impedance of the amplifier, as in Fig. 3. It is easily shown Fig. 4. Geometry of voice coil and gap volume. that the power in the load is s term in the second brackets at length. Pi= ° - 1 . (1) R1 Since this term contains much of the RI information which determines the effi- 11 ciency, its algebraic manipulation will To digress a moment, note that E'/R1 be described in some detail. Resistance is the load power if the source im- may be expressed in terms of conductor pedance R, were zero ; hence the second length I and cross section area A by R = factor on the right expresses the devia- pl /A, where p is the resistivity. Thus Fig. 5. Measurement of effective cone dition from this condition caused by finite l' /R =PA/p/= lA /p. But IA is the ameter d. volume source impedance, and hence is also a of the conductor. Set this volume limiting :measure of the damping effect of the equal to a fraction of factor. Hence the gap -energy a the total gap vol- term in amplifier on a speaker load. The term ume V, which is the efficiency reflects the eco- defined in Fig. 4 to in- nomics of speaker manufacture, regulation has been given to the quantity clude that in the voice coil overhang. The and aids fracton in comparing speakers ; neither the flux a is the space factor, and is a density nor the flux measure of how total will permit D =20 logo (/ + .f) . (2) efficiently the voice direct comparison. The coil makes use of the magnetic use of Alnico V flux den- in place of Alnico III is an example sity available. Now suppose that the of For properly loaded push -pull 6L6's, : while magnetic this the cost per pound of V is the regulation is about 15.5 db, while a energy W in the gap is de- greater, it has over termined by the measured three times the pair of 6B4's will have a regulation near flux density, energy per pound, so that the cost per using the relation W = 3.5 db. If sufficient feedback is used, D B'V /bar. Then million ergs is less, offsetting even some can be reduced to as little as 1.0 db, al- B' =81.W /V. Thus after all substitu- of tions the mechanical problems of fastening though 3 to 5 db is nearer average B'l' /R, becomes 8,raW/p, where Alnico V magnets in place. W is the gap It is mag- commercial practice in high -quality magnetic energy in ergs netic energy the customer pays for, not sound system amplifiers. To measure and p is the voice coil resistivity in gauss or maxwells. D, simply load the amplifier properly ohm -cm. The space factor a can be improved and read the output voltage. Then re- If all the piston -range substitutions by using a rectangular or ribbon shape move the load; D is the db rise in out- and approximations are made in the instead of circular for the voice -coil put voltage. In the so- called constant - efficiency formula, there results conductor. However, if a reasonably voltage audio distribution system, D r 2.44 x 10-' high impedance is needed, the ribbon is 3 db or less. 0.3 CaW must be made quite thin, and then the To return to the main topic, it is seen 1 inter -turn insulation may be a very that the efficiency is given by R,R I (m/d ' ) '' appreciable fraction of the total thick- ` s 1 RI ness. For ordinary direct- radiator 10 -rv'rr Rt 1 +R01 speakers, the space factor -which in- R1 (3) (ergs, grams, inches) cludes allowances for clearances as +t=Pi EDs well (5) as insulation and precision of wire lay By calculating the cone velocity to be Here C is the ratio of the conductivity (see Fig. 4) -may be about 20 per expected when the connections of Fig. 2 of the voice coil to that of copper. The cent. Voice coils of edgewound ribbon are used, the following expression finally coefficient in brackets has the following sometimes reach 30 per cent by also results : values for these output stages : PP6L6, omitting the bobbin, but one sturdy no feedback, about 2.6x10 -9; PP6L6, enough for use in a "woofer" should R, Ra +Rt considerable feedback, (6 db regulation) offer only a slight advantage. The n Rt 2.9x 10-9; and PP6B4, 3.1 x 10-9. To re- theoretical advantage should be that of - R, +R,+ 10-' (Bl)' \ peat, a is the space factor, the fraction the square over the circle, or 27 per )ti of the gap volume used by the voice coil ; cent gain. The actual gain cannot be r(Bl)'1 r W is the magnetic gap energy in ergs; very great, for the coil -to -pole -piece 1 s (4) m is the total effective moving mass in clearances required in low- frequency x L R. JL(rr' +4u'f'm')J4r"sr x10. grams ; and d is the effective cone diam- [Continued on page 42]

14' AUDIO ENGINEERING AUGUST, 1951 A Two-Tap Bass and Treble Compensated Volume Control

WILLIAM O. BROOKS`

A simplified analysis of the method of determining the constants for a loudness control which will simulate the Fletcher- Munson curves to a reasonable degree of accuracy.

NYONE who has adjusted the un- work as described by E. E. Johnson? compensated volume control of an For those in the radio manufacturing A amplifier when music was being industry where cost is a great factor, a played has noted that as the control was good but cheaper method might be de- rotated from its full volume position to sired. its minimum, less and less bass and It is possible to make two well located treble were heard as compared to the taps on a single control approach the amount heard in the maximum or full - desired boost requirement to a very ac- volume position. This is borne out by the ceptable degree. This has been done in commercial radio equipment for many Fletcher-Munson sound pressure curves Fig. 3. Volume control with single tap, allow- appearing in engineering texts. As the years in the form of one or two tap ing for one bass turnover frequency. curves show, it is necessary to boost volume controls ; however, only bass

the bass -and to a lesser degree, the compensation was obtained. On recent C2 treble-more and more as the control designs treble compensation has shown de- C2 is lowered to make up for the hearing up on a single- tapped control. The RI curve of the ear. velopment of a two -tap control with both e-RI By adding a tap on the volume control bass and treble compensation, as pro- R4 R2 and running the sliding arm down to posed by the author, is to be discussed 113 R2 this tap we have an "L" type tone com- in this paper. Let us start with a single R3 Cl pensating network as shown in Fig. 1. tapped volume control as shown at (A) Cl The network can be figured so as to give in Fig. 2. If the slider is set at the tap. correct compensation for hearing losses we have an L pad divider made up of at this one point. Now it becomes ap- R, and R, as shown at (B). The voltage (A) (B) ratio will he R, /(R, +R,). If R,= meg, then 0.25 meg and R1=0.25 Fig. 5. Development of dual -tap control. 0.25 0.5 , or 6db attenuation of 0.25 + 0.25 it is necessary to insert R, in series with voltage. If C, is now connected from tap C,. At the frequency when the reactance to ground as at (A) in Fig. 3, we would of C, =R, the curve will begin to flatten have a definite attenuation of voltage at out. This frequency is known as the bass some desired center frequency. Above turnover frequency. It is subject to this frequency, the reactance of C, de- change with each design engineer from creases at a constant rate, attenuating a minimum of 250 to a maximum of the highs. Below this frequency, the 1000 cps. Since 800 cps has been chosen of the audio Fig. 1. Basic arrangement of components for reactance of C, increases at a constant as the center frequency L -pad compensation of frequency response. rate, thus effectively boosting the bass spectrum, a bass turnover frequency of (by attenuating the high frequencies). 1000 cps will tend to raise the midrange 250 turnover will Since this bass -boost circuit should not too much, while a -cps not allow the bass to rise to a suffi- R1 the expense of losing treble, function at ciently high amplitude. It is thus desir- R2 able to stay within 250 and 1000 cps. It I "A continuously variable loudness con- R2 [Continued on page 47] trol," AUDIO ENGINEERING, Dec. 1950. 4RI (A) (B)

I MEG CONTROL Fig. 2. Simplified equivalent of uncompensated MONIT. LEVEL 66 +100 dD OVE (BASS TAPS) TAPS) volume control. 0.33 MEG OVER (BOTH

TAP 35Oo1, TREBLE TURN - OVER (TOP TAP) to 100 per -10 parent that in order have a v 0,161 ME6 B000^UTREBLE TURN - cent perfect control, we would have to TAP OVER (BOTTOM TAP) have an infinite number of taps on the of net- 15 . control with an equal number Fig. 4. Response cur- a ....4 1' works. This is impractical from ves for dual -tap con- o mechanical and economical standpoint. trol shown in the NJ -so /M11 Ilie boxed -in schematic. The next choice would be three con- 17 kin .70 db III trols back to back on the same shaft - La one acting as a volume control, one as Cc +eodbrn000PeI- a continuously variable bass-compensa- uI_-1'1l tion network, and the other a continu- i \11== mini ously variable treble -compensation net- II ' +50db 10 no moo law f ". * Senior Engineer, Hoffman Radio Corp., FREQUENCY IN CYCLES PER SECOND 3761 So. Hill St., Los Angeles 7, Calif.

AUDIO ENGINEERING AUGUST, 1951 15 Audio and the Armed Forces

Lt. GEORGE MARAKAS, USN

The Armed Forces Radio Services combine the production and technical facilities required in a network headquarters with the processing facilities of a major record manufacturer. All illustrations are Official A.F.R.S. photographs.

IF YOU WERE TO ASK a GI overseas his are recorded for the AFRS basic music favorite stateside address, next to library. At present the Service is ship- home of course, its a better -than- ping early 40,000 16-in. 33 1/3 r.p.m. even chance that he would mention 1016 Vinylite recordings monthly. All ship- North McCadden Place in Hollywood. ments are made by high -priority air and It is from this address that a cargo of originate in Los Angeles, where most more than 6000 transcriptions originates of the recording is done and where all each week, consigned to radio stations transcriptions are processed. of the Armed Forces Radio Service, and Just as AFRS steps beyond the destined to bring a little bit of home to boundaries of service and rank in the American Doughboys, Sailors, Marines, selection of its personnel, so does it and Coast Guardsmen in China, Alaska, operate without restriction in the choice Korea, Germany -in fact, wherever of equipment to perform the various they're doing their job. To these fight- functions of recording and broadcasters for democracy, transcriptions mean ing. A visit to the Remote Recording information, education, and entertain- Section will disclose a veritable hodge- ment from back home. podge of the best known trade marks in The Armed Forces Radio Service is the audio industry. A recent remote unique in the fact that it is a unified recording job, for example, made use of command dating from the early days two Stancil- Hoffman type R4 tape of 1942 -long before the major services recorders, two Western Electric 22 -D teamed up. Known colloquially as "The portable mixer -amplifiers, three RCA Voice of Information and Education," 44BX microphones, and one Altec Lan- AFRS is a completely merged Army - sing 21B condenser microphone. Each Navy -Air Force operation, functioning Technician checks grooves on transcription be- of these items was chosen by Vernon ing cut on Scully lathe in Recording Section. under the Armed Forces Information McKenny, Chief of the Section, because and Education Division, Office of the of its unique ability to perform some Secretary of Defense. Its Commanding specific function. It can be seen from Programming Officer is Col. William M. Wright, Jr., this that AFRS is operating virtually Supervision and programming AGC, U.S. Army, while Major Clifford of without equipment limitation in its ef- AFRS is a task comparable to of Frink, USA, is Executive Officer -Chief that forts to maintain highest audio quality operating a large commercial network. of Operations. in all of its programs. The In its overseas transcription AFRS "network" consists of sixty activities, A visit to the AFRS headquarters in stations ranging in power from AFRS writes and produces approxi- 25 watts Hollywood discloses one of the coun- to 200 kw. It can be seen from mately 16 hours of programs weekly, this that try's best -equipped sound studios. Under procurement and installation alone are including the famous "Command Per- a single roof are five studios, formance." twelve prodigious chores. In addition, mainte- In addition, more than 50 soundproof rooms for auditioning, a nance hours of programs must be considered. Add to this are taken from the recording equipment room, facilities for the job of providing major networks and de-commercialized, each of these sta- editing tape, a thoroughly equipped tions with 63 hours of programming and approximately 60 musical numbers shop for repair and maintenace, and weekly and producing 13 hours of pro- a master control room for shortwave gramming daily for shortwave distribu- Liaison Officer, Armed Forces Radio broadcasting. tion, and Service, Hollywood, Calif. the full magnitude of the Following the practice established by AFRS radio operation becomes ap- commercial broadcasters, AFRS records parent. a number of its programs on magnetic Shortwave operations are maintained tape rather than on acetate discs to fa- from both Los Angeles and New York cilitate program editing and assembly. over eleven transmitters beamed to all This is of special importance where parts of the world. West Coast trans- network programs are to be de -commission totals 1777 hours monthly over mercialized. The studios are equipped seven of the stations, and East Coast with two Ampex type 200 recorders, transmission totals 450 hours over the ten Stancil- Hoffman type R4 recorders, remaining four. Program schedules from and three Gates control consoles. To Los Angeles begin at 5: 15 p.m. (PST) maintain quality in keeping with high- and end at 6 : 30 a.m. Newscasts are est commercial standards, the bulk of aired on the hour, compiled from the tape recording is handled at 15 in. per three major news services, State De- second. After being recorded on tape, partment and Office of the Secretary of programs are dubbed on acetate, pro- Defense releases, and other recognized Navy Radioman 2c David Cleveland shown dis- cessed, then pressed on Vinylite for news sources. AFRS also shortwaves cussing disc on turntable in recording section shipment to AFRS stations throughout prominent baseball and football games, of AFRS with Ralph Zerbe. the world. as well as outstanding boxing matches.

16 AUDIO ENGINEERING AUGUST, 1951 AFRS, while primarily concerned Top right. Private James Ross, AFRS technician, Minitape with informing and entertaining Amer- checks operation of Stancil- Hoffman recorder before sending it out on a remote. ican forces overseas, is acutely con- Bottom right. One of three Gates speech input scious of its important role as the voice consoles used in recording the hundreds of reaching behind the Iron Curtain and weekly programs. into those areas dominated or influ- Bottom. Group of three Stancil- Hoffman tape enced by the word from Moscow. recording machines used in the Shortwave department. Mounted on dollies, these machines Ninety million listeners in all parts of may be moved readily from studio to studio. the world turn to AFRS, as well as to the State Department's "Voice of Amer - ica" programs, for news of the USA. And although it is not true that AFRS is the official voice of the U.S. Govern- ment, these millions accept what they hear from AFRS as an accurate. un- doctored reporting of events at home and abroad. Through AFRS's informa- tional and educational programs, they learn the reasons underlying our pas- sions for the American way of life. WHODATHUNKIT- A Was Born in California

HEN THE IDEA for bringing out a eared copies of If'estern Stories -at the rial group took the advertising boys up special Pacific Coast issue first editorial staff's disposal for proving or on their offer. hold in the Æ office, the disproving the legend that lE was a W took Backward, Turn Backward mental giants therein immediately ap- child of California. Kipling notwith- plied the full weight of their monumen- standing, the twain met -and the edito- Research, to an advertising man, tal intellect to the task. The crea- means digging out reams of facts NUMBER S tive ability inherent in this notable VO LUME 1 and figures designed to prove this group is sharply evidenced by the or that point about markets, circu- originality and design- for -action in lation penetration, etc. To an editor their first move -an editorial con- seeking to verify early events, how- ference was called. One member of ever, research has a different mean- the staff, a displaced Californian ing. naturally-came up with the rea- It offers a chance to lose one's soning that all good things originate self in the delicious nostalgia of west of Arizona -so that by follow- the past -to partake once more of ing the obvious we could easily youth and its fancies -and, in the conclude that ìE was California case at hand, to re -live those days born. Hot feature item for a special when DX was anything further West Coast issue. away than next door, and the aver- The comptroller-opportunist, he age "old-timer" shared concern over -seeing a chance to throw his the efficiency of his rig with anxiety weight around, and forgetting mo- about to date on which his voice mentarily the fate that usually over- would c Lange. who takes bookkeepers venture Retrospect opinions on editorial matters, said, in simple words, no soap. Then - JANUARY. 1920 11 10-N (UNIS Let's turn back the pages of radio realist, he- sensing that his neck history to the romantic and thrilling was out a mile, and doing a slow year 1917. DeForest, Cunningham, burn with the dawning realization VICTORY Moorhead and other notables in the that he was a downtrodden minority art of placing a grid, a plate, and a of one, he modified the monolithic EDITION filament into a piece of glass tubing quality of his impetuous outburst to known as the Audion, Audiotron, say he'd go along with the idea, IN THIS ISSUE: and other analogous trade names, providing that the California birth TREE RADIO TELEGRAPHY were vieing with each other to cap- of lE could be proved. The editorial NEW LIST OF LICENSED AMATEURS ture supremacy in the great new group, not entirely unmindful of LATEST RADIO NEWS field which was ripe for the har- expense accounts and salary checks, vest of their earlier endeavors. acceded with becoming grace. The magic lamp of the "wireless" At this stage of the discussion tn....d 0.1. P..A, days was destined to revolutionize the advertising staff entered the act. the infant, industry of communica- Between ill -stifled yawns they con- Earliest existing copy of Pacific Radio News, antecedent tion. Manufacturers of such gadgets siderately offered to place their en- of Audio Engineering, from the archives of the New as variometers, tickler coils, grid tire research facilities-three dog- York Public Library. . [Continued on page 57]

AUDIO ENGINEERING AUGUST, 1951 17 Constant - Resistance Dividing Networks

BOB HUGH SMITH'

A presentation of the design parameters for dividing networks which use two coils of equal inductance with two identical capacitors.

practical advantages over the second. These are: (1) It requires about 15 per cent less inductance in the low -pass section, and hence, for a given wire size the insertion loss is about 7% per cent less. (2) It requires about 15 per cent less capacitance than the second. (3) When feeding from a zero impedance source each section of the first type is down 3 db, while for the second type each section is down 4 db, thus the second type results in a one decibel dip at crossover. Fig. 1. Schematic of parallel configuration of (4) The input impedance of the first constant -resistance dividing network. type is exactly equal to the character- TiIERE ARE Two principal types of istic impedance of the filter and contains no reactive dividing networks in extensive use - component, providing the the constant -resistance network and network is terminated in pure resist- Fig. 3. Chart showing length of wire for given the "m" derived half section network, ances. The last two points are of more inductance. Example: If the required inductance academic than practical II 5 ml,, approximately 290 feet of wire will be and the first type has several minor significance. needed for the coil. The design procedure for the constant - *University of California, Berkeley, Calif. resistance network is really quite simple. The values of inductance and capacitance are read from the chart, Fig. 2, once the \C characteristic bi o i o atT / impedance of the filter and \ 4i , cross -over frequency have been selected. ¡a\Walv..r.1 esAe. ABU d'w CL1Is.7t'ATLisc.^.67 21:01:11W Jr.107Li'auriCa::/ 9r i\i.'.OY1MiiL"s:OO:i>..A0.?iDiO's.YC'....i:f!%i'iC Next, the wire size is 04::S.,OTaÓ*ilüi7.i0C.';r:..i.iC.iC113 _..,.. y.:tw .L I`.i1p..C9 r ::: chosen from the Oi_ .t.:C+.iauacaSL:i:'A`dV401iri!Q:1'r/0ßOZp following considerations : (1) If the wire %:W4.7 kq. Yd Fr / CWA2ai2.s'09d01ie//A`;: Òa, ,o size is too small, the insertion loss of the V!O9m.a0gri:/mg:eÓOi%w1eàgÁ . low -pass section will be excessive, and Asl kl\\tái K4AilppgiEi NAPZERI, JÁ, (2) if too large a wire size is chosen, the inductances become inconveniently w /:.ioiog!pÓr. w obvSr r~r,li 1s ' /.40iw.- i-1ö:R bulky. A satisfactory compromise may be %:V !/'%., made by choosing a wire size which will . i` result in a coil resistance equal to 10 per I\a11:I ÌLY,:e7A,v,OitE'w\\_1Í-IV.OVOpp\\ÒVI1,ik//¡`,sglii¡ cent of the characteristic impedance of MINNiv..-s.190:1rm.:acaMM.aI..a:0..ib.m.oeeNItOZ\.Ti'V.42111iSGigPISI tl17avs:97E101'0ji` 0"::1i..arA`ÓraO`í1C®n..e.i....a.a o:aolll ..r... o..nuis+ the filter.This produces about one deci- MPIO i i!.11.:0:4` iO.Y.aCCMPZï Ci7i :111/a0Òd\0®MMV iKIi:A,i bel loss through the low -pass section and . A&....,:OeòCao. dIA:. K.NR:AeiOeC/.0Z -iN i: ::Oi.iZiMMIII0MiA?KS-We.ÓLIONi"_::z:.I:iIe'11INIg:Mi:aor , is undetectable on complex signals. The approximate length of wire needed may i!i :i1i !ib! ï 1:!iii iiii íié,%p be obtained from Fig. 3, and the wire t: h,.áI% d size may be selected from Fig. 4. ibi, r1/i Vwwwi ,»;>r.14I.i':i w w Ï Y rf- V"MA% Next the coil is wound to approximate r, 1 j¡q /ïñ size using the length of wire already de- , termined, and then turns are either re- iIÓv,SOÖv000'ii://iGi % ¡o1sIVYIYEki ,,:r-Yde' ar moved or added as required to provide s>a\\. iZPrspiOiJOFíltt`s?*' t_C.%iqQOLi\1:eIirarAs/1R7RriÍ r iÌii% :.::ivi4nÖ!ICi0..-:: .4a`CJCr40::'.+.*4iirCL` uOL.S:C the exact inductance. If an impedance , so/.....-r_+ilooacaï,.+: :'i'_:d:Y.A01/%QíQf Ci,311,:T.0:9S ..i'iii.-- ."e4` a..C4..Ip000JOO:,.e,`. 4 - `:.aQavepNii.o::,:a::AnCc: s . bridge is not available, the scheme shown ''%Qwaaii \i.1%If'%!C`.:cv' ww+.ìN ._ 70Ì%I!I'I% / ...i\ta\Is'P! !' ! in Fig. 5 may be used. When the in- í.%ILQI.\\.I,=r ,.1,1\' ir!' .a\Ga% 1PGr14r!-' A.CIOA,\;r.1r; .+ea,-eea ductance is of the correct value, the volt- r- t r `ï ' ì''' I o i'. meter indicates the null to occur at the 7g .04r" ' \ \..: A 'MOIRA.w w w ::;oiiiii':t:ls+iii'''.'.;i,;s...o,iw .Nr i:o_a1.w w ies.. crossover frequency. If the null is below ..4 . .p KMa1%i';`, 1-3!í,id.A4:q *N7 io the crossover frequency, the inductance I-!i;. is too high and turns must be removed; ñéq4i9 ii:. 1P Ì¡/Nlii.`1Pi:i'id if above, the inductance is too low and 1 !-i * 1 . 1 0 ' 00 F 1000 10íl00 turns must be added. This method has the advantage, over the impedance bridge CROSS-OVER FREQUENCY - CYCLES PER SECOND method, that it automatically compensates for error in the capacitance. Thus, Fig. 2. Chart for determining constants for network. Example: Suppose pedance the characteristic im- it is not necessary to have precision ca- Is 11.5 ohms and the desired crossover frequency is 500 cps, then the inductance should be 5.0 mf and the Vance should be 20 µf. pacitors, but they should be of either

18 AUDIO ENGINEERING AUGUST, 1951 the oil or paper type and should be non - inductive.

Design of Network The following example may clarify the procedure of producing a dividing network. Suppose it is desired to design a crossover network for a 16 -ohm two -way speaker system. One might select 1,000 cps as Fig. 6. Frequency re- the crossover frequency and 16 sponse of constant ohms as the characteristic impedance. resistance network. Figure 2 indicates that the inductance should be 3.5 mh and the capacitance should be 7.0 µf. Referring to Fig. 3, it is seen that a coil having an inductance of 3.5 mh will require about 240 feet of wire. Figure 4 indicates that the resistance of the coil will be about 1.6 ohms if 418 wire is used. Since it is easier to remove turns from the coil than It is evident that the slope of the curve in each stop band is 12 db per octave. Mill= The effect of the coil resistance in the :n:ui= = low -pass section is to provide almost Fig. 4. Chart showing uniform attenuation throughout the pass length of wire vs. re- but to in stop for various band have little effect the sistance band. The effect of the coil resistance in 1s gauges. Example: A coil resistance which the high -pass filter is negligible in the is 10 per cent of the pass band and also in the stop band down ® characteristic imped- ta,a,iie ance results in coils to the frequency for which the coil re- ,I of practical size. Since actance becomes equal to coil re- the impedance is 11.5 the ohms and the approx- sistance. Below this frequency the slope imate length of wire 6 db is 290 ft., 4$16 wire becomes asymptotic to per octave. should be used. Thus, for the case in which the coil re- Aiiar sistance is 10 per cent of the characteristic impedance of the filter, the high - pass section drops 12 db per octave from crossover down to 7 per cent of the to add more to it, about 275 feet of wire The expression for the transmission of crossover frequency, and from then on is measured out and wound into a coil. the low -pass section is: is asymptotic to 6 db per octave. Actu- The process is then repeated, since two ally, this is hardly significant for a prac- tc 7 of such coils are required. Two 7.0 s.f ca- tical network since at per cent crossover the attenuation is already 46 db. pacitors are connected in the circuit of K.20 log f \ Fig. 5, using a 15 -ohm resistor for Re. - I/f fç Is +2 Suppose it is found that the null occurs to /I at 800 cps; then turns are removed until and the expression for the gain of the the null occurs at 1,000 cps. The coil is high -pass section is: OSCILLA - taped and checked again in the circuit of TOR Fig. 5 to be sure that the tape has not JIMI fe pressed the wires closer together and K=20 log thus increased the inductance. Next the t _fe ` Fig. 5. Equipment set -up used to adjust in- +2. ductance. Turns are added or removed to obtain coils and capacitors are mounted and to t a null indication on the voltmeter at the cross- wired, completing the network. These expressions are plotted in Fig. 6. over frequency.

Is Your Ear Tin or Golden? Step Right Up and Get Your Answer Headache Saver Announcement of the 1951 Audio The feature is expected to create a Many of the headaches usually asso- Fair, scheduled for November 1, 2, and high degree of interest among those ciated with the solution of complex 3, in Manhattan's famous Hotel New sharp -eared high- fidelity enthusiasts mathematical problems are eliminated Yorker, has already started the ingenu- who are constantly boasting about their by the latest "thinking machine" devel- ity of many exhibitors working at top superior sense of hearing. Each con- oped by Friden Calculating Machine speed. testant will be given a token "Golden Co., San Francisco, Calif. Lafayette Radio, for example, has Ear" as evidence of his having partici- Capable of extracting the square root cooking a plan to give every visitor to pated in the contest. of 10-digit numbers in nine seconds, its display a "Golden Ear" test to de- This test should provide some en- termine the frequency range of his hear- lightening comparisons between the without use of tables of any kind, the ing. According to Irving Frisch, La- hearing characteristics of persons with machine is entirely automatic-extracts fayette advertising manager, the idea is training in the field of audio, and those square roots and automatically points being developed in the form of a of the population as a whole. off the correct decimal in the root "Golden Ear" contest with prizes posted Note : There is some question as to through entry of the number and touch for the winners who prove their "ear whether the Lafayette exhibit should of but one key. superiority." To ensure absolute fairness be illuminated with red lights to mini- The machine is expected to ease in the contest, all measurements will be mize the visibility of red faces. Sugges- greatly many of the mathematical as- made with an Audiometer. tions are in order. pects of engineering and electronic design in many industries.

AUDIO ENGINEERING AUGUST, 1951 19 A New Approach to Loudspeaker Damping

WARNER CLEMENTS

Modestly styled by the author as "the hottest thing in audio," positive feedback added to a negative- feedback amplifier is shown to reduce output impedance to zero or below, achieving a damping factor of infinity.

IS APPRECIABLY BETTER LOUDSPEAKER you have been successful in doubling "ringing." There is more to it than that, damping really attained by increasing your damping ratio from 4 to 8 -thus but the yardstick thus suggested is a use- the damping ratio of amplifiers higher cutting output impedance from 4 ohms ful one for underdamped systems. Cer- and higher ? The answer, sadly enough, to 2 ohms-you have, for your pains, cut tainly ringing contributes largely to the is "No !" Some lowering of the other- total effective generator resistance only characteristic "loudspeakerish" sound wise very high impedance of a pentode from 15 ohms to 13 ohms. Actually you from which all direct -radiator speakers amplifier is desirable, and there are other haven't even done that well because in seem to suffer. To induce ringing in any concurrent benefits obtained from the use either case additional damping has been underdamped system it is only necessary of the same negative feedback which re- contributed by the mechanical resistance that an impulse be introduced which duces apparent output impedance. How- of the cone suspension. contains components higher in frequency ever, it appears that there is a wide- It is justifiable to take voice -coil re- than the resonant frequency of the sys- spread misunderstanding of the princi- sistance, normally considered as part of tem. The familiar "mouth-harp" is an ples involved. the load, and add it to the source, for two example of such a system. The pitch of In this article, the author will en- reasons. First, as in the case of motor the vibrating part of the mouth -harp deavor to show that we have been de- rotor windings, resistance and self -in- does not vary. Yet when placed in the hiding ourselves to a great extent about ductance of the voice -coil are necessary performer's mouth, tunes are produced the merits of a high damping ratio, and evils and contribute nothing to per- by tuning the cavity (formed by the that there is a way to achieve high damp- formance. Second, the voice -coil param- mouth) which the initial transient starts ing other than by the application of more eters are effectively in series with, not ringing. Circuit switching can produce and more negative feedback. By the shunted across, the "business" part of widely differing sounds in different method to be described herein, it is pos- the load. If one measures the electrical speakers. This writer once arranged a sible to take the damping ratio right up impedance of a speaker at a given fre- half -dozen speakers of various sizes and to infinity and beyond. In fact, it is in quency and then impedes the motion of makes so that he could play a simple the region well beyond infinite damping the voice -coil, the impedance is seen to tune with the thumps created by closing ratio that an amplifier must operate in go down, being lowest with the voice - toggle switches connected between the order to provide theoretically perfect coil completely blocked. At this point the respective voice -coils and a dry -cell. Fine speaker diaphragm control. By the addi- voice -coil shows the same impedance that tuning was accomplished by changing tion of only one inexpensive part, your it would if completely removed from the baffling. In no case was the speaker in- own amplifier may be transformed to operate either at infinite damping ratio, or at a condition of near -perfect electrical damping. Let us examine the principles involved in amplifier- damping of loudspeakers. L MM Take an ohmmeter or bridge to the nearest speaker and measure the d.c. re- LMM is inversely proportional to stiffness of suspension sistance of the voice coil. Ten ohms is a Cum is directly mass representative value for a 16 -ohm RUM is inversely resistance L. is directly ocousticol copocitance of oir lood speaker. Now measure the resistance of CIA is inductonce 16 -ohm secondary of an output trans- RIA is inversely resistance former. Another ohm or so. Now add the 11 ohms thus obtained to the tiny ap- Fig. 2. Equivalent circuit for motional impedance of loudspeaker. parent output impedance-0.6 ohms, maybe? -you have obtained in your speaker except that its inductance is stallation any different from one which amplifier, perhaps with considerable ex- affected somewhat by the metal sur- might have been intended for sound pense and circuit complexity. Doesn't rounding the gap. Conversely, if a reproduction. This experiment suggests look so good, does it? For instance, if weightless voice -coil could be suspended one reason why two -way systems are in the gap so that it could move freely likely to not sound good to the layman. * Box 969, Sherman Oaks, Calif. without encountering stiffness or fric- If the pitch of the click of the high -fre- tion, the electrical impedance of the quency speaker bears an inharmonic re- r-- speaker Rvc Lvc Z¿I would be infinity. The total elec- lation to the pitch of the thump of the trical impedance of the circuit will allow- frequency speaker, a disagreeable SPEAKER ways be greater than that of the voice- noise is produced on every transient TERMINALS El - coil alone unless the speaker is inopera- which is to say on least a at every note of L__ _J tive. Clearly, then, the equivalent circuit music and syllable of voice reproduced. is the series 1. PVC . VOICE COIL RESISTANCE one of Fig. It is clear that damping is a de- LyC VOICE COIL INDUCTANCE sirable objective, but it is also clear that ZM IMPEDANCE DUE TO MOTION OF Transient Response VOICE COIL beyond a certain point inverse feedback Good transient performance is often does virtually nothing toward attaining Fig. 1. Electrical equivalent of loudspeaker load. equated to the reduction of overshoot or this objective. Actual tests with pulses

20 AUDIO ENGINEERING AUGUST, 1951 exact amount of positive feedback necessary varies with the installation. With a typical high -efficiency speaker and a fairly high amount of negative feedback, the ideal amount of positive feedback to be added will be found to be that amount which just about doubles the gain. Cir- cuit algebra shows that this means the Fig. 4. Method of using negative impedance to achieve perfect damping. effective negative feedback will have been cut in half. In other words, the and interrupted wave -trains show that a and into the negative region if desired. principle is applicable to any circuit from triode output zoithout feedback represents The ideal setup, then, is to use voltage which you can get roughly 6 db more of about the point of vanishing return. A proportional negative feedback plus feedback than you really need from a lower output impedance than that thus current -proportional positive feedback. standpoint of distortion. This will in- represented is of very little importance Direct and inverse feedback can thus clude most high- quality amplifiers and in restraining the ringing of a typical be used simultaneously without cancel- practically all triode amplifiers. Figure diaphragm assembly. Direct -radiator ling each other out, although cancella- 5, drawn from actual 'scope traces, shows speakers will ring at their resonant frequency even if fed by a generator of zero internal impedance. Just how badly they will ring under that circumstance Fig. 5. Waveforms will depend on the amount of flux in the across output of neg- gap and upon the amount of damping ative- impedance am- inherent in the diaphragm suspension. plifier with 30 -cps The role of mechanical damping, which square -wave input. takes place mostly in the outer roll, is Speaker resonant fre- illustrated in Fig. 2. The power that quency =120 cps. (A) INSUFFICIENT NEGA- (B) TOO MUCH NEGA-11_EGA- (C) PROPER ADJUSTMENT goes into Rm,a, shown in the middle TIVE RESISTANCE RESIS ANCE circuit of that figure, is the power that counts -the power that represents acoustic output. The shunting reactances tion occurs insofar as the distortion -re- that the combined feedback principle are necessary evils. Any power lost in ducing and frequency-response -smooth- works out as neatly in practice as it does ing effects of inverse feedback are con- in theory. It also illustrates the quickest cerned. But with regard to reducing ap- and easiest way to adjust the amount of parent output impedance, the effects of positive feedback applied when one of the the inverse and direct feedback are addi- circuits to be described is added to an tive. Referring to the block diagram of amplifier. Note that if too much positive Fig. 3, it will be seen that any voltage de- feedback is used, ringing resumes, but is veloped only in the load causes the input now reversed in phase. voltage to be modified in the sane phase Figure 6 shows a circuit that has been by the resultant out -of-phase voltages in recommended for applying positive feed- Fig. 3. Arrangement for applying voltage - the two respective feedback circuits. The back to the popular Williamson ampli- proportional negative feedback simultaneously operation of the circuit is as follows: fier. It would seem that this circuit has with current -proportional positive feedback. starting with negative feedback alone, several drawbacks. Since it applies feed- the edge damping, is power wasted the apparent output impedance goes back before even-order harmonics have Rmm, is It from the standpoint of efficiency. Never- down as positive feedback applied. been bucked out, it increases the magni- of positive theless it can be seen that a low value of requires only a slight amount tude of those harmonics and lessens the it zero. Damping - Rm,a will do much to minimize the feedback to bring to likelihood that they will be perfectly of infinity. effects of the shunting reactances. ratio at this point is, course, cancelled. Since it introduces constant - impossible to get all of the way As more positive feedback is added, the current negative feedback, it defeats its It is becomes to zero apparent output impedance by apparent output impedance own purpose up to a point and requires means of negative feedback. Even as- negative and starts to "erase" the series high output from the driver tubes. it were possible, the speaker part of the speaker load impedance. At Finally, since ordinary ganged potenti- suming that is would still not be cured of ringing, be- some point the voice -coil impedance ometers run well above 10 per cent cause of the intervening impedance of exactly matched by the negative imped- "tracking error," the signal balance of flux -density in the ance of the amplifier and theoretically the output stage is likely to be rather bad. the voice -coil. High illus- gap can reduce the effect of the voice perfect damping is achieved, as The circuit of Fig. 7 was devised by feedback is coil, but cannot eliminate it. But suppose trated in Fig. 4. If positive the writer in 1949 and is believed to be increased considerably beyond this point, far superior to that of Fig. 6. It is easy that it were possible to make the ampli- In fier exhibit negative impedance as viewed oscillation will eventually occur. to apply to existing amplifiers using any from the output terminals. The negative actual installations it may take place of the popular circuits and the single before the midband gain gets up to what adjustment has no effect on push -pull impedance would subtract from the This voice -coil impedance. If the two just it would be with no feedback at all. balance. It may be seen that a split -load latter is due to the difficulty of securing an type of phase inversion is applied to the matched, the effect of the would im- entirely. is no exact phase match between the load positive feedback, permitting it to be have been eliminated This impedance. idle dream, but is, in fact, quite easy of pedance and the negative returned to the same point at which the is of only aca- attainment. The means is positive feed- This last consideration negative feedback is applied. This keeps interest, however. There will back. Readers will recall that constant - demic phase shift identical in the amplifier from output always be an ample safety margin before part of both positive and negative feed- voltage inverse feedback an of the causes apparent output impedance to de- oscillation, even if the inductance back loops. If desired, the phase- inver- feedback voice -coil is ignored and the amplifier is sion feature can be left out and the posi- cline, while constant -current resist- causes it to rise. With positive feedback made to exhibit a pure negative tive feedback applied to grid of same the opposite holds-voltage- proportional ance. stage, as shown in Fig. 8. This circuit is feedback causes the output impedance to satisfactory where the damping is de- rise and current -proportional feedback "Perfect" Damping sired only at the lower frequencies. The lowers it. Furthermore, current -pro- Thu, perfect damping is arrived at stray and interelectrode capacitance to portional positive feedback will take the long before the benefits of the negative ground from the top of the grid resistor output impedance right down past zero feedback have been cancelled out. The prevents the higher frequencies from

AUDIO ENGINEERING AUGUST, 1951 21 justing for the least boominess. When loading have been depicted as variable. you are through, you will have an out- In general, the circuit values due to fit that provides the cleanest reproduc- definable mechanical parameters are tion you have ever heard from direct - relatively fixed. Those due to acoustic radiator speakers. This is, of course, values may vary with frequency, even provided that other things are right. the equivalent inductance and capaci- Bear in mind that no amount of damping tance. Over a wide range of frequencies in one circuit will dampen another reso- where the speaker (if considered as a nant circuit that is but loosely coupled perfect piston) gets a big enough "bite" to it. For instance, if a room resonance of air, the loading due to air is almost is present-it is almost impossible to get purely resistive and is constant with fre- away from it in small rooms-no amount quency. For the equivalent circuit within of speaker damping will obviate it. Look this range Cm,, and Lma could be left com- out also for acoustic feedback to turn- pletely out, and Rma could be shown as table or microphonic tubes. fixed. However, if the applied frequency is lowered far enough, the "bite" will Limitations cease to be big enough at some fre- Now for the bad news. A generator of quency that depends on the size of the low or negative internal resistance is in cone and the resistive loading will start Fig. 6. One method of obtaining current -pro- some regards not an ideal device to change. Whether it may be said to go portional positive with feedback. which to drive a loudspeaker. Some "up" or "down" depends upon the writers, acoustical -electrical analogy one being fed back, describing the performance of uses even without the in- (e.g. force- current or force -voltage). At clusion of R and C. Rp may be a volume any rate, the net effect is that the re- control if desired. sistance "seen" by the electric circuit, OHMS. NOMINAL SPAR. R. in Figs. 2 and 4, goes up with de- Negative Inductance IMPEDANCE la TO PRASE INVERTER creasing frequency. An interesting refinement on the NEG. FEEDBACK DROPPER Figure 9 shows the variation of Rm negative- output -resistance amplifier is to with frequency on the assumption that make it display negative inductance Rm is entirely due to the air loading on as Lf Rf well, thereby cancelling out the in- the cone. (In different speakers, the ductance of (SEES contribution of will the voice -coil and improving TEXT) Rmm flatten the high- frequency response and stability. actual rise of the curve to various de- LAST SINGLE - OUTPUT grees.) This can be done by including an in- ENDED STAGE TRANSF. The "turnover" frequency, ft, ductance in series with the positive -feed- will vary from about 520 cps for a back rheostat, as shown dotted in Fig. 7. 15 -in. speaker to about 1,660 cps for a The optimum value for this inductance Fig. 7. Preferred method of applying positive 5-in. speaker. It can be seen that loud- feedback. is given by the formula : speaker response will drop off about 6 db per octave below this frequency if an LNG effective constant voltage is applied across Z. (since the power output will Where A' is gain of part of amplifier then be inversely proportional to Rm). enclosed by feedback loop, with negative But the ordinary amplifier, with con- feedback only and unloaded. To apply siderable output resistance adding its this formula, you need to know LD, the effect to that of the voice-coil, will drive blocked voice-coil inductance of your a speaker in such a manner that there speaker (or speakers). Unfortunately, I will not, in general, he such a low -fre- know of no way to block the voice -coil quency attenuation. The reason is that of a speaker securely without injuring it, the reactive part of the motional im- so even if a means of measuring in- pedance, as at (C) of Fig. 2 "looks ", ductance is available it will do no good above resonance, like a capacitance unless the speaker has an electromagnetic shunting the load. Together with output field. In that case the effect of blocking resistance and voice -coil resistance it Fig. 8. Variation can be achieved by simply leaving off the of Fig. 7 that produces low - forms a power- eating tone control cir- field frequency boost but damps speaker only at one cuit that flattens out the current. low frequency, which response be- If you are prepared may be set to be resonant to tackle it on a frequency of the speaker. [Continued on page 54] cut -and -try basis, you can assume that the blocked voice -coil inductance of a amplifiers of high damping ratio, have 16-ohm speaker is about 1 millihenry and spoken of the "apparent" lack of lows start from there. Such a coil should be and have gone on to imply that the ear toroidally wound of #16 wire on an air of the listener needs retraining; that the 256R,, core. Connect the coil into the circuit lows are there all right, just less con- and add or remove turns until a value spicuous because of lack of resonance. is found that permits Rt to be advanced Actually the lows are attenuated more 64% the furthest (greatest resistance) with- and more as damping is applied. With out oscillation taking place. Actually the circuits of Figs. 6 and 7 the loss of there is nothing critical about this in- lows will be very pronounced with some ductance. If it permits Rr to be turned speaker arrangements, though negligible at all further than it could be without with others, as will be explained. 4ft. the coil in the circuit, it will improve the It has to do with variation, with fre- operation of the circuit. After turns on quency, of the air loading on the speaker RO) coil are adjusted, R, can then be ad- cone. In (B) of Fig. 2L the resistance justed to its final setting by means of and LoO°wsiaiö reactance contributed to the equiva- ti 4ff 16ft 64f1 square waves applied to amplifier and lent electrical circuit of the motional 16 4 'scope across speaker terminals, as in impedance by the mass and mounting of Fig. 5. It is also possible to do a fairly the voice-coil and cone have been de- Fig. 9. Variation with frequency of resistive good job by ear with program material picted as fixed. On the other hand, re- consisting of male component of air loading on diaphragm, using speaking voice by ad- sistance and reactances arising from air the force- current analogy. 22 AUDIO ENGINEERING AUGUST, 1951 Acoustical Balance in Recording EDDISON von OTTENFELD, Mus. D..

A musician expresses his viewpoint on the old and continuing controversy between engineers and musical directors -but with an understanding of the problems of both. score and the use of instruments EVER SINCE the turn of the century- comes charged with slightly veiled in- the - when the introduction of mechanical sults. The conflict begins, of course, with mainly on how they are used. Much of devices for the recording of sound a lack of knowledge by the parties con- our work is in a cappella recording. As a in evolutionary degrees the cerned. However, the practice of riding result, our first approach to this medium captured mechanism tremendous musical contribution of the gain and knocking the top off of climac- is the analysis of the physical world's greatest composers-there has tic passages in music is not the answer which produces speech as a sound -pro- been a division of opinion as to what to proper acoustical balance. It might, in ducing vibrator in resonance chambers balance in record- some instances, smooth over a rough for acoustic waves. We know, for ex- constitutes acoustical waves ing. On the one hand we have the ques- situation, but the problem as a whole lies ample, that during speech these is basi- tionable opinion of music directors and in the scoring and use of instruments. are changing constantly. This other the adamant viewpoint of There is no such thing as a perfect music cally true with instruments. The only on the in sing- the recording engineer. Actually, it is a score that can be recorded with the same manner in which proper diction the music director trying results when used for radio, commercial ing has been attained is to get the chorus battle between The simplest to obtain the inspiration he hears in the recordings, motion -pictures, or choral to think and act as a unit. recording engineer work- work. These separate techniques are well way to overcome diction problems is to music and the vowel ing with his equipment to keep what he established in themselves, and the engi- agree on the emphasis of the Neither of these view- neer is obligated to know how each itself. When this is accomplished, the records in balance. are points is necessarily correct. There has medium is handled. Without this knowl- end results in soft and loud passages in engineering, but edge, nothing but a questionable re- the same. been much progress that a lot more can be added to the art of cording result is attained. When the engineer understands recording. The phenomena of sound is par- the bass, tenor, baritone, alto, or soprano in acoustical balance has ticularly satisfying as a branch of sections are subject to tonal variations, The interest of been gradual because the knowledge of physics, but sound in a tonal sense is not he is usually able to correct problems science of acoustics has been in- necessarily measured accurately. Tonal- tonel and diction by having each section the the di- complete. All evolution, as we know of ity is often unpredictable. What is true sing as a group, alone, and with A director it, is a gradual process of unfoldment with reed instruments is not necessarily rector monitoring the results. understanding. Engineers in true with brass instruments, especially invariably is impressed with these and better between the recording industry have spent count- where the many types of mutes are con- peculiarities in tonal variations well as groups. On -the- in improving their techniques ; cerned. The same is true with the vari- individuals as less hours or a those who are best informed spend just ous stringed instruments-even indi- spot corrections can then be made the problem. as many hours in understanding music. vidual instruments of the same type- different scoring applied to engineer knows his music although they may be playing the same The engineer should understand the A progressive when sung as well as his profession. This is evident musical passage. With human voices we relative intensity of vowels of chorus. The in all recording studios of repute. have the greatest challenge. by different sections the research has contributed to The engineer must do more research intensity of bass will frequently over- Invaluable If the the development of the telephone, radio, of his own. Much has been accomplished shadow the soprano, for example. radar, recording, and motion picture with reflection and absorption of sound soprano section is singing in consecutive in all forms of in the recording studio, but it is not thirds, it frequently causes "shattering," sound, as well as Inversion of acoustical reproduction. Many times enough. The real problem is in inter- both in tone and diction. through chance pretation of the music, and this de- tones then should be applied to overcome progress has been made are discoveries and through a genuine co- mands a full working accord between the problem if the singers themselves contribu- engineer and music director. The engi- unable to control their tones. No jug- operation among engineering out this tors to perfect their scientific medium. neer should be able to analyze the musi- gling of equipment will iron Unfortunately, there is no scientific cal score to determine if it is acousti- problem. or the creative cally correct for recording. If perfection The engineer is in an excellent posi- evaluation of inspiration a of the individuals who have is the goal, the engineer and music tion to determine what is wrong with process music interval given their lives to compose the world's director can discuss their problem in- score if he knows why a were such a thing as a telligently and iron out their difficulties overlaps. as in the case of consecutive music. If there where over- yard stick with a scientific approach, before the recording is attempted. thirds. The same is true be analyzed. Be- In all of our work, we check the lapping of intensity occurs in each sec- creative music could the cause of this. the engineer must take a repertoire thoroughly before we attempt tion of the chorus. If he can explain to the subject and a recording. We know the problems in- physics of sound to music directors they different approach for put as much study and application to volved and we are prepared to meet are not only impressed but grateful individual musical selections as he does them. Ironically, there is no problem his knowledge and suggestions. in maintaining and perfecting his equip- that cannot be met when musical knowl- ment. edge and scientific engineering get to- Choir Recordings gether. The inspiring end result is a Sonie of the choirs which we have Conflicts contribution to our culture, for through recorded have produced what we con- recording. countless thousands of listen- sider perfectly balanced recordings. St. I am always amused when a serious they the music di- ers are able to audit music which Olaf Choir of Northfield. Minnesota, is conflict ensues between have no opportunity to hear. rector and the engineer. Each assumes normally one of these. It is under the direction of Christiansen. Little need be said that he knows his subject better than the Arrangements Olaf other fellow, and the atmosphere be- about the St. Olaf Choir, so well known In general, concert arrangements in because of its concert tours and its radio music do not necessarily adapt them- broadcasts. Many observers feel that the selves to radio, phonograph recording. * President, Volala Records Inc., Holly- [Continued on page 58] wood, California. or motion pictures. The problem lies in

AUDIO ENGINEERING AUGUST, 1951 23 Toward a More Realistic

An AES Paper Presented October 26, 1950 Audio

ROSS H. SNYDER

A complete, frank discussion of the trend in equipment development which is necessary to provide the discriminating listener with optimum reproduction in the home, if the consumers' demand is to guide the engineers.

Tins FIRST, Is, a report on the atti- to inform: we owe them a profound making the necessary tudes Consumers' Research interconnections has found debt of gratitude. in their assemblies. Much hum, commonest among those interested and most N f Unfilled reports of unreliable performance are in high -fidelity in the home. CR receives Demand for traceable more inquiries Audio Systems to this difficulty. Often when on this subject than on the supplier has not any other except automobiles, volunteered full in- so we Non -professional high -fidelity enthusi- formation on the necessary wiring, believe we are dealing by no means with asts, we the find, are more interested in good non -technician is at a complete loss. an insignificant minority. Common fac- record -playing equipment than in any- A fourth too tors in these inquiries have importance thing else. Radio is most -common complaint is often regarded made over the difficulty to those in the profession. as an accessory, to be used of laying out for inci- an assembly so that the Assemblies of high -fidelity compo- dental listening, but not as a primary controls come source out symmetrically and at one central nents have been well received by con- of serious musical entertainment. point, sumers. We are much impressed so that duplication among them is with There is an important minority of non- avoided, and so the willingness they show to make sub- that convenience of technician consumers which is interested operation is optimum. The physical stantial investment in their equipment. in home con- recording. These are almost ex- figuration of the equipment is blamed. It is surprising that so many are ask- clusively concerned today with magnetic Related ing, not for the "best low -cost equip- apparatus, with tape commanding most to this objection is the series ment," but for the "best available." En- inquiries. of inquiries on how to arrange the equipment in couraging as this may be, there are Another matter either built -in or cabinet widespread of wide concern is set-up so that the final assembly looks danger signals of conse- the consumers' inability to hear quence to everyone in audio. and see neat and professional. It is said that ex- the equipment before purchase. Many pensive arrays The amount of misinformation re- still are unaware of fine equipment should that well- equipped look well enough to justify their cost. flected in our inquiries is appalling. sound salons are maintained by dealers Some of what passes for quantitative Nobody, it is suggested, short of a combi- in the larger metropolitan areas. nation data in advertising is, we believe, down- architect and electronic engineer Many purchasers of assemblies inform could assemble, re- arrange, and alter right misleading. Some of it may be us that they experience written by people who are, themselves, difficulty in some of the components on the market, misled, but much of it appears to be de-

1 liberately misinforming, composed with I 1 1 I -I full understanding 1 I I that however am- 15ALUMINUM-DOME DIRECT RADIATOR biguous the impressive figures may be. Speaker Fr 58 even professionals are enormously in- Vented Enclosure: V 6.1ft3 Fr 59 cps fluenced by graphs and charts that ap- 40 Effective Amplifier Internal E 0 Ohms pear to be derived from measurements Eve 5.7 Constant (2 Vil in 16 ohms) +IS

Frequency Response - on ------equipment too complex and expensive ----. Distortion to be familiar. - +10 Aside from the advertisements, the r m I 30 I ° dealer himself too often sponsors con- z I 'S I o - w fusion cc in the buyer. There seem to be t two common types: the one who first Cr t 0 O -_L N feels out the customers' prejudices, and , w then feeds on them; and the type which 0 20 a assumes an Olympian attitude toward N - _._- E 2 . . . _. . . all mere customers -an attitude whose x . -10 =O loftiness is the best measure of its ig- to norance. There are, of course, the 10 honored few who ~s,s 15 offer respect and seek ` . . __ . . . fi . . -20 * Audio Engineer. NIBS, San Francisco. - Calif., and Audio Consultant, Consumers' `...... Research, Inc., !. I Washington. N. J r 2 ) ! 6 _25 (Consumers' ! r e r i ] Research is a non -profit organiza- s 100 1000 tion which examines a targe variety of consumer i0000 goods and makes reports evaluating them, in a FREQUENCY IN CYCLES PER SECOND published Bulletin.)

Fig. 1. By no means a "horrible example," this is one of the most highly- regarded of contemporary Responsibility loudspeaker systems. The measurement for the contents of this was made outdoors from the top of a high building in silent location. a paper rests upon the author, and state- It should be noted that the amplifier source impedance was artificially reduced to ments absolute zero (constant contained herein are not binding -voltage) conditions. The bass characteristic assumes somewhat more normal proportions upon the Audio Engineering Society. when the source has some, if little, effective internal impedance. The 1000 -cps dip may be due to rim resonance or to a cancellation arising out of cabinet conditions. 24 AUDIO ENGINEERING AUGUST, 1951 so as to avoid ugly cabinet proportions, eccentric lumpy shapes, and trailing wires. To most of us here the most important objection raised by non -technical people is this: many expensive assemblies don't sound good enough. The specific complaints most often received are with respect to noise, shrillness, and weak or dirty bass response. This is not with reference to users of faulty equipment, either. Now, presumably, the reason we make measurements in designing and building equipment is in order to pre- Fig. 2. A high -quality dict, in the scientfic sense, the end home system in which re- control complexity sult to be obtained, namely listener sat- has been reduced to isfaction. If we refuse to recognize a a minimum. listener's objections on the ground that he is incompetent, we are ignoring a serious discrepancy in the accuracy of our predictions. A refusal to admit that the experimental results disagree with the predictions is an inexcusable viola- tion of scientific method, and can't be tolerated. Before we conclude that the listeners are mainly tin -ears, and retire to the laboratories to please no one but ourselves, we had better re- examine our measuring methods and their interpretations. It is suggested that the trouble lies with simple and attractive, but un- realistic, interpretations of our evidence. We're not relating the physics and the of frequency -range will improve the lis- of the speaker system. This amounts to psychology of the problems before us in teners' reactions. Still better listener- between -23 and -40 dbm, representing an adequate way. Our engineering. it is reaction is observed if, instead, further performance which, with a nominal 10- suspected, is excellent, but our psy- reductions aré made in noise, distortion, watt amplifier, would be described as chology needs an overhaul. We are pre- and raggedness. We think that in this "Noise 63 to 80 db below full output." occupied with the glamorous means we direction, laboratory predictions and The first figure is not hard to attain, but are using to the point that we're for- listener reactions may be brought to co- the latter, when high -gain magnetic getting the ends toward which we should incide. pickup preamps are in the circuit, is be working. rarely achieved, representing noise cor- Suggestions for Improvements of responding to a noise -input level of -118 Acoustic Quality dbm. The listener who wants quietness Listener Preference These, then, are our impressions of enough to pay two or three hundred the most significant needs of the home dollars for his amplifier expects to have Our findings indicate that listener sat- this demand met. Lower -cost installa- isfaction increases with increasing fre- user, and a theory from which we think better satisfaction of those needs can tions will, presumably, involve speakers quency -range only when noise, distor- of lower efficiency, especially at the tion, and raggedness of frequency re- grow. On the basis of these needs we suggest expanded criteria for judging hum frequencies, and will meet the response are all greatly reduced simultan- quirement with the higher noise figure. eously. To be sure, there is nothing new components and assemblies, to include about such a theory. Many investigators not only (1) highest possible acoustic Record Scratch Limits quality, defined in terms of listener sat- feel these are the culprits in the public's Take another example: how much notorious distaste for wide -range sys- isfaction, but also (2) convenience of installation, maintenance and operation, record-scratch is tolerable? When we tems. Yet, many of us continue to display integrate several factors together at attitudes-and equipment -which over- (3) appearance matching or excelling that of comparable -cost production con- once, we find that the character of the emphasize wide range to such a degree scratch is at least as important as its that, by comparison, noise, distortion, soles, and (4) reliability and safety above any reproach. relative level. If the sound- pressure re- and raggedness are ignored. Equipment sponse of a whole system is full of dips is commonly designed to pass 30 to 15,- and peaks, scratch causes objections out 000, or even 20 to 20,000 cps -the very Noise Level Limits of all proportion to its level. But if the limits of human hearing-yet how miser- To evaluate audio quality realistically system is smooth throughout its range, ably short are we still of getting noise by means of physical measurements, we and that range does not include much down to the threshold of hearing, of re- have to integrate them together at every more than the cleanly- recorded fre- ducing distortion to the point where it's point. Quantitative standards are neces- quencies, the silky character of the undetectable, or of reducing acoustic out- sarily arbitrary, so it is best to make hiss is tolerable when its measured put that is free of dips and peaks. Ex- them marginally more exacting than the level is as little as 25 db below peak tending range is easy, and therefore majority of cases requires. To illustrate recorded signal; with modern record- tempting. But extending range without how much electrical noise is tolerable, ing means it can be reduced much correspondingly improving noise, dis- we find that listeners are displeased if more than this -and it should be. and smoothness characteristics, such noise, in the absence of signal, is tortion, Pickup Cartridge is costing us listeners. We think it can- audible a few feet from the speaker. The not be overemphasized that in a system In our tests the electrical output, in tube - A common source of gross distortion of any range -wide or narrow -noise, noise and hum, that was just audible and intolerable raggedness is the align- distortion, and raggedness are not suf- varied between 0.1 and 5.0 microwatts, ment of the cartridge relative to the ficiently reduced if the listeners don't depending upon the level and character record, especially in changers as they like the sound. Sometimes a reduction of ambient noise and upon the efficiency are installed by dealers, some of whom

AUDIO ENGINEERING AUGUST , 1951 25 or an amplifier at the point where response is just measurable, on the tail - end of an 18 -db- per -octave declination, but the practice is apparently common in rating loudspeakers. We think the industry is sufficiently grown -up today Fig. 3. A high- quality that it can afford to apply the same rig- home system in which orous standards to speakers that it does the necessities of to other components. component construc- If the speakers merely cut off the top tion have led to dup- and bottom, it wouldn't be so bad. But lication and complex- the distortion that results in the middle - ity in control func- range when a cone is driven out of the tions. linear portion of its magnetic gap by boosted 40 -cps fundamentals makes a strong argument for electrically restrict- ing the bass range. The same holds for the top, when the ragged residue of response goes to work on the harmonic structure. Horns help a great deal in the top range, of course, but if they are to seem to have the impression that the think, inadequately measured at the low begin handling power at 800 or 1200 cps cartridge is properly installed if its percentage -modulation used in standard their diaphragm -mass forces a fast roll - stylus manages to contact the record test procedures. With the high modula- off from 6000 or 7000 cps. The value of surface once each revolution. If gross tions routinely maintained nowadays, adding a miniature third unit for the disorders of this kind are relieved, the there is need for drastic improvement in extreme top is questionable, since in our loudspeaker becomes the limiting factor. detectors. FM distortion may be ex- experience its function is largely to As response -smoothness improves, the pected to be below 1 per cent with +75 make a fine display of the hash to be upper tolerable range, we find, can be kc swing and 50- microvolt signal, at found there from almost all program extended. which 40 db of quieting should be ob- sources. Provision for cutting off the served. Such a standard is attainable top electrically should be provided in Distortion Limits and is, we find, required in many loca- every quality installation. If our listeners tions to satisfy critical listeners. set the cutoff lower than we do, we When we consider distortion limits might inquire what distortion products we have to integrate them with power We come last to the question of frequency-range because we are so firmly and jagged responses up there drove requirements. At the risk of extended them away. Control of the high fre- argument, we report that oscilloscopic convinced that this is the last place where improvement should be sought. quencies presents more complexities observations at the final grids of a num- than the usual controls allow for. If ber of amplifiers in actual home service, It will appear sheer heresy to speak of a high- fidelity system whose range is horn speakers, or others of good distri- using musical transmissions with low - bution and smoothness, are used, sharp efficiency speakers, showed no peaks good only from perhaps 70 to 6000, or 60 BUT IF WE MEASURE IN cutoff points are needed to minimize driving the amplifiers beyond 5 watts, to 8000 cps. TERMS OF ACOUSTIC OUTPUT, ACCORD- program- source irritations. If ragged even when uncomfortably high sound - by levels ING TO THE SAME STANDARDS WE APPLY speakers are dictated economics, were developed. With high -ef- gentle roll -off of the whole upper range ficiency TO FILTERS AND OTHER ELECTRICAL ELE- speakers the signals were con- is demanded, we find, by listeners. Very siderably lower. Furthermore, when MENTS, THE LOUDSPEAKER IMPOSES SUCH LIMITATIONS. That this is due to no form sharp cut -offs, or, worse, peaks followed peaks of this power, transient or other- the wise, of carelessness or lack of research by by sharp declination, produce same drive virtually all our tested exces- into loudspeaker makers does not obviate the sort of listener -irritation as does speakers violent distortion, we feel sive raggedness. that a 10 -watt is necessity that we recognize the problem amplifier which un- Where bass response is concerned, critical of its is enormously complex and difficult. load at any usable fre- we find once more a widespread en- quency, is generous, and that expense For this reason we feel required to consider the limitations of the best speaker gineering reluctance to take the listener incurred for greater power is extrava- seriously. If he prefers a loud one -note- gance. We find that which the economics of any given instal- such an amplifier electrically- measured flatness, contributes no audible if lation will permit when we select every thump to unpleasantness there is entirely too much tendency to the following conditions are met: dis- other component. We believe the profession owes the speaker- makers the charge off the trouble to the listener's tortion must decline with power, and at tin ear. Reconsideration indicates that the 10 level must not compliment of recognizing the magni- -watt exceed 2 per flat acous- cent r.m.s. tude of their problem, and that we ought many electrically systems are at any frequency from 40 to tically decidedly weak at the bass end. 7000 cps. IM distortion of 8 per cent is to discredit the misconception that such alternately acceptable a range as 30 to 15,000, or 20 to 20,000 We customarily drive speakers from ex- if the frequencies tremely low source -impedance ampli- are 40 and 7000 cps separated by 12 db.1 cps is now expectable with anything re- Pre -amplifier and tone -control sembling the smoothness and low distor- fiers, so that the power expressed into stages the speakers at their high -impedance must be included, and must not, in tion we realize routinely from the elec- except bass frequencies, is low. Furthermore, treble -boost or bass -cut positions, in- trical components. We can find no evi- crease these figures. dence that any speaker or system ac- loudspeakers work into living -rooms whose Distortion in AM receivers is, we complishes such a standard. See Fig. 1. dimensions do not encourage ex- Only the costliest systems we have excitation at long wavelengths. Because higher source impedances involve us in 1 It has been shown elsewhere, by C. J. amined produce a recognisable 40- or 50- LeBel and others, that the relation be- cps tone, much less one of low distortion. serious damping problems, some pro- tween total r.m.s. and IM distortion is by The hash which most speakers make of vision is needed to lift the voltage output no means a simple or a constant proportion. the range above 4000 or 5000 cps may approximately with speaker impedance. To the conditions defined here needs to be best be judged by the jaggedness of their Further boosting will be needed to over- added only the condition that distortion- response- in come the living -room's unfriendliness content shall decline regularly with its har- curves that region. Even the monic vital mid -range is full of points of vio- to low frequencies. The boost should number in order to make the mean- not ing of the 2 per cent r.m.s. figure coincide lent disturbance. Where frequency -re- be extended too far down, of course, with that of the 8 per cent IM distortion sponse range is concerned, no engineer or the amplitudes involved will drive the figure. would rate the "upper cutoff" of a filter [Continued on page 52]

26 AUDIO ENGINEERING AUGUST, 1951 NEW WIDE RANGE 5Kc to 50 Mc -12 Volts output BRIDGE OSCILLATOR

Type 1330 -A Bridge Oscillator ... $525.00

WIDE FREQUENCY RANGE: 5 kc to 50 Mc, carrier COAXIAL OUTPUT jacks, cable and adaptors permit complete s/tit'lding from to measuring instrument THREE MODULATION FREQUENCIES: internal a -m at line and at 400 oscillator c and 1,000 c, at two levels of approximately 30% and 60% LOGARITHMIC DIAL: from 5 kc to 15 Mc GOOD OUTPUT: 12 volts, open circuit; % watt into 50-ohm load INCREMENTAL -FREQUENCY DIAL: indicates increments of 0.1% kc to FREQUENCY ACCURACY: Carrier: 2% above 150 kc, 3% per division from 5 15 Mc below, no load. Audio: 5% for 400- and 1,000- cycles LOW DISTORTION: between 1% and 6% at 60% modulation LOW LEAKAGE: about 50 uv per meter at 1 Mc, two feet from level; r -f distortion 3% over most of range oscillator VERY COMPACT CONSTRUCTIONS panel relay -rack width, only 7 inches high; cabinet 9 inches deep EASY SERVICING: oscillator plugs out of shielding box and has servicing cable to test instrument

The new Type 1330 -A Bridge Oscillator is designed especially as a power source for bridge and general laboratory measurements. It is relatively inexpensive, has high output and excellent mechanical construction throughout. Oscillator assembly plugs into deep brass box; double cover completes shielding. Note servicing cable permitting instrument to be tested on bench.

Typical Set -up

Measuring characteristics of r-f coil. Types 1330 -A Bridge Oscillator, 821 -A Twin T Impedance Meas- uring Circuit and a communications -type receiver. The oscillator is equally suited to use with other bridges such as the Type 716 -C Capacitance Bridge and the Types 916 -A and 916-AL R -F Bridges.

275 Massachusetts Avenue Cambridge 39, Massachusetts

6 St., Los ANGELES 920 S. Michigan Ace., CHICAGO s 90 West St. NEW yolk 1000 N. Seuard v

Since 1915, Designers and Manufacturers o #1. Precision Electronic Laboratory Equipment

AUDIO ENGINEERING AUGUST, 1951 27 Seventh Annual Pacific Electronic Exhibit Pacific area comes into its own with mammoth display of electronic equipment -Held in conjunction with Western Convention of I.R.E.

0 MORE EMPHATIC means of drama - Ironic Corp., is president, the APEE Credit for success of the APEE may tizing the swing of industry to the rotates annually between northern and be found in the teamwork of its officials N West could be devised that the southern California. Alex W. Fry, Elec- -helped along, of course, by the famous seventh Annual Pacific Electronic Ex- tro- Engineering Works, is chairman of "native -son" complex with which all hibit, scheduled for a three -day run be- the WCEMA exhibit committee. The West Coasters are imbued. In addition ginning August 22 in the San Francisco Exhibit has displayed a consistent an- to Mr. Byrne and Mr. Fry, other civic auditorium. Held in conjunction nual growth of 20 per cent, both in ex- WCEMA officers are: Fred W. Falck, with the annual western convention of hibitors and in attendance, and today Advance Electric & Relay Co., vice - the I.R.E., the APEE this year will be ranks with the two New York shows- president; A. C. Davis, Cinema En- considerably larger than the 1950 show the Audio Fair and the I.R.E. Conven- gineering Co., secretary ; and Norman when 66 eastern and 30 western manu- tion -and the Chicago Parts Show as H. Moore, Litton Industries, treasurer. the "big facturers exhibited. In addition to com- four" of the industry. Manager of the annual Exhibit is mercial displays, number This year, for the first time, the Heckert Parker. a of prominent program will colleges, universities, and APEE include special Board members of the WCEMA are government sessions for manufacturers and jobbers, Herbert Balderson, Therillador Electri- agencies will participate. Attendance is with attendance limited to qualified rep- cal Mfg. Co., Los Angeles; Robert Bell, expected to exceed the ten -thousand resentatives. In addition, two forums Packard-Bell Co., Los Angeles; Orrin mark. have been arranged for executives, pro- H. Brown, Eitel- McCullough, Inc., San The theme of the 1951 exhibit is "Be- duction, and operating personnel of Bruno; William Gates, Dalmo Victor hind the Scenes in Electronics" and, planufacturers and wholesalers, both of Co., San Carlos; E. P. Gertsch, Gertsch despite the fact that many of the elec- which will be open to all visitors to Products, Inc., Los Angeles; L. W. tronic items being produced today are both the Exhibit and the Convention. Howard, Triad Transformer Mfg. Co., on the classified list, exhibits are being Thus the Exhibit will combine the best Los Angeles; John Kaar, Kaar Engi- designed to animate the various proc- points of an engineering forum, a man- neering Co., Palo Alto; Noel Porter, esses involved in all branches of elec- ufacturers' display, and a business con- Hewlett Packard Co., Palo Alto; Leon tronics manufacturing, beginning with ference under a single roof. Ungar, Ungar Electric Tool Co., Inc., raw materials and carrying through to Principal speakers at these meetings Los Angeles; Russell Varian, Varian finished products. will be Donald F. Marshall, chief, In- Associates, San Carlos, and Messrs. The I.R.E. portion of the activities dustries Planning Board, Western Air Byrne, Falck, Davis and Moore. will include presentation of many im- Procurement District, USAF, and Glen Cooperating with the WCEMA in portant technical papers, field trips of McDaniel, president, RTMA. conducting the exhibit are members and Mr. Mar- officials of The Representatives of Radio general interest, sight -seeing excur- shall will discuss regulations and ex- sions, and Parts Manufacturers, Inc. The San a special program for enter- plain procedure covering government Francisco will tainment of chapter staff the message the ladies. procurement of electronic equipment, center under the directorship of Dave Established originally in 1945 as a while Mr. McDaniel's subject will be Ross. When the exhibit occurs in south- non -profit venture by the West Coast Where the electronic industry stands ern California, this function is per- Electronic Manufacturers' Association, now and its part in the Nation's pre- formed by the Los Angeles chapter with of which Paul F. Byrne, Sierra Elec- paredness program. Norman B. Neely as chairman. List of Exhibitors and Booth Numbers AMPEX ELECTRIC CORPORATION 805 BERMAN, E. L., COMPANY 223.24 A Redwood City, Calif. San Francisco 3. Calif. High- fidelity magnetic tape recorders. Sound equipment, electronic and TV components. ADVANCE ELECTRIC a RELAY CO. 208 Burbank, Calif. E. G. Swanson. M3Ton Stolarof, Waiter Selsted, Frank E. L. Berman, Ed Brandt, Jack Berman, Howard liar. Electrical relaye. Lannert. wood, Sidney Harman, P. N. Cook. See adv. IN Page 57) (See adv. on Pap 55) B IRD ELECTRONIC CORP. 311 ANDREW CORPORATION 122 Cleveland 14. Ohio. AEROVOX CORPORATION 606 Chicago Termaline RF wattmeters, coaxial Itches. LF filters. New Bedford, Mus. 19, Ill. ew Capacitors, Coaxial transmission Ilnee, communications antennas and L. E. Bird resistors. accessories, tower lip ht Ing equipment, dry air equIp- BROWN ELECTRO-M EASUREM ENT CORP. 212 We,. Hilt. Charles Meyers, At RI,sl. ment, Portland AIRCRAFT and related Items. 15, Ore. -MARINE PRODUCTS, INC. 112 ARNOLD ENGINEERING COMPANY 316 Impedance bridges, bridge amplifiers and related equip - Harrisburg, Pa. Marengo, Ill. ment. Solderlen wiring devices, radar pulse networks. Permanent magnetic materials. cast Alnico mag nets, BRUSH DEVELOPMENT CO. 509 Wm. H. Knowles, Jr., Thomas II. We!shy, O. W. e ntered magnets, Vicalloy. Remalloy, Conico, Conile, Cleveland 14, Ohio. Holmee. cast cobalt magnet steel. Also h permesbi lily m te- Test instruments, amplifiers, direct- writing ose I I lo. AIRTRON, INC. 611 rials, De !tam as toroidal cores, Supermalioy toroidal graphs. Linden, N. J. cores, Permendur. B URGESS BATTERY CO. 106 Weveguldes, switches, directional coupler,, mixer du- (See adv. on Page 3) Freeport, Ill. piller assemblies, dummy load,. AUDIO SERVICES, INC. 605 Complete line of dry batteries for standard and special 1ItTEC LANSING CORPORATION 225 Nvw York 22. N. Y. applications. Beverly Hills, Calif. Recording dites and tape. Dave Miller, Phil Crocker, Vern Rupp, L. H. Marri . Loudspeakers, amplifiers, tuners, transformers, micro- Alan H. Bodge, Herman Kornbrodt. B URLINGTON INSTRUMENT CO. 507 phone,, consoles, intermodulation test equipment. (See ado. on inside front cover) Burlington, Iowa. A. A. Ward, Ed Grigsby, John K. Hilliard, E. B. Har- AUTOMATIC ELECTRIC SALES CORP. 120 A.C. end D.C. electrical indicating instruments. rison, W. W. Simmons. Chicago 7, III. Walter Connan, David II. Rose. (See adv. on Page 43) Telephone-type relays and switches. B USSMAN MANUFACTURING CO. 113 AMERICAN MICROPHONE CO. 515 K. A. Regel, V. E. James, J. E. Bunt, A. D. Boehm, St. Louis 7, Mo. Pasadena 1, Calif. Jr. Fuses and fuse holders. Microphones, phono pickups. AVERY ADHESIVE LABEL CORP. 108 O. A. Alderman, N. S. Beyer. Cramer Yarbrough, G. N. Christensen, William W. Monrovia, Calif. Vogel. Pressure -sensitive labels. (See adv. on Page 61) Howard Black, W. G. Proper, John S. Torrey. C AMERICAN PHENOLIC CORPORATION 116 CANNON ELECTRIC CO. 613 Chicago 50, Ill. B Los Angeles 31, Calif. Coaxial cables and connectors, AN connectors and fit - HERB BECKER Electronic and electric eonneetors. tinge, antennas, radio components, plastic, for else. Los Angeles 15. Calif. Don A. Davis, Floyd Cate. troll) cl. Electronic Components and equipment of various manu - (See adv. on Page 6) R. ES W. AM COMPANY 109 facturera. I VISION, GLOBE -UNION San Francisco 7, Calif. B ERKELEY SCIENTIFIC CORP. 713 CORP. 501 Aluminum and steel chassis, boxes, cabinets, frames Richmond, Calif. Milwaukee 1, WI,. and containers for electronic assemblies and end equip- Frequency meters, electronic tachometers, hishspeed Controls, switches, ceramic capacitors, printed else ment. counters, nuclear equipment. Ironie circuits, Steatite. Earl Hellas. G. 11. Bruns, Jr.. Ernest C. Heime, M. C. Burne. W. S. Parsons, Wickham Harter, Robert A. \iii II,r.

28 AUDIO ENGINEERING AUGUST, 1951 JAMES P. HERMANS CO. 117 CHICAGO TRANSFORMER DIVISION. ESSEX ELECTRONIC INSTRUMENT CO. 807 222 Brooklyn, N. Y. San Francisco 3, Calif. WIRE CORP. Electronic components and equipment of various well - Chicago 18, III. Electronic test instruments and kits. Claude Erlanger. known manufacturera. Transformers and renters. SOB J. T. HILL SALES COMPANY 220.21 P. N. Cook, E. I.. Berman. John 11111. ERIE RESISTOR CORP. Erie, Pa. Los Angeles 15. Calif. (See adv. on Page 37) capacitors, Electronic stop watches, oseillographs, cathode -ray tubes. CINEMA ENGINEERING CO. 422 Ceramic capacitors, button silver mica printed ceramic trimmers and suppressors. Osc I l lograph- record cameras. Oscilloscope time calibre. Burbank, Calif. circuits. analyzers, Oscillo-tracers. magnetic re- A. K. Shenk, D. H. Ross, W. H. Davis. tors, spectrum Precision wire -wound resistors, attenuators. J. T. (Jerry, 11111, John T. Hill, James J. Hill, Janes cording tom ',anoints and related Items. L. Wells. James 1.. Pouch, Arthur C. Davis, David Roes. F RUSS HINES CO. 101 (See ado. on Page 36) San Francisco 3, Calif. CLEAR BEAM TELEVISION ANTENNAS 102 FAIRCHILD CAMERA & INSTRUMENT Eleetronle equi pment and components. Los Angeles 38, Calif. CORP. 519 R. W. Moulthrop, A. A. Hines, G. M. Moultbrop. Antennas and lead -In. Jamaica 1, N. Y. HOFFMAN RADIO CORP. 322-23 CLEVELAND ELECTRONICS, INC. 619 Precision potentiometers. oscilloscope recording cameras. Los Angeles 7, Calif. Cleveland 3, Ohio. H. E. Dale, E. Larralde, E. Mennen. Television receivers and other electronic equipment. Loudspeakers. HYCOR CO.. INC. 625 COASTWISE ELECTRONICS CO., INC. 313 North Hollywood, Calif. Beverly Ili Its, Calif. G Precision resistors. torold coils, decade Inductors. Television accessories and test equipment. (See ado. on Page 52) CORNING GLASS WORKS 408 GENERAL ELECTRIC CO. 520 Corning, N. Y. Syracuse, N. Y. radio trans- TransmItti nil, receiving. Industrial, and cathoderay Glass bulbs, tubing and pans for TV, radar, arms. mitting and receiving and other electronic applications. tubes, test equipment, phono cartridges, tone GENERAL RADIO CO. 418.19 Cambridge 39, Mass. INDIANA STEEL PRODUCTS CO. 409 Precision electronic test equipment. Valparaiso, Ind. D (See adv. on Page 31) Permanent magnets. GERTSCH PRODUCTS. INC. 706 INSTITUTE OF RADIO ENGINEERS 802 DISTILLATION PRODUCTS INDUSTRIES loo Angeles 25. Calif. New York 1S, N. Y. (Division of Eastman Kodak Co.) 411 VHF frequency meters. radar power supplies. Prn erding5 of the I.R.E., membership applieatlene, and Rochester 3, N. Y. E. P. Gertsch, Leonard S. Culler, Robert S. Hood, D. general I.R.E. Information. High -vaeuum equipment. Fuller. INTERNATIONAL RECTIFIER CORP. 614 Carl W. Iferrlaano. GIRARD- HOPKINS 403 Los Angeles 43, Calif. DRAKE ELECTRIC WORKS. INC. 502A Oakland L Calif. Selenium rectifiers and photo cells. Chicago, III. Fixed paper capacitors. Phi 11p Diamond. Soldering Irons and guns. GOODYEAR AIRCRAFT CORP. 808 -9 ALLEN B. DU MONT LABORATORIES. AIRUn 15, Ohio. INC. 813.14 GEDA (An electronic differential analyser) Clifton, N. J. GUARDIAN ELECTRIC MFG. CO. SOSA Cathode -ray tubes. Chicago, Ill. JENNINGS RADIO MANUFACTURING CO. 806 I. G. Rosenberg, W. C. Scales, R. G. Scott. Relays. San Jose 8, Calif. Vacuum capacitors. vacuum micro -wave transformer. H vacuum switches and components. E HEINT2 g. KAUFMAN DIVISION, The Robert THOMAS A. EDISON, INC., Instrument Dollar Co. 107 K 607 Redwaud City. Calif. Division CO. 417 West Orange. N. J. Transmitting tubes, specialty communications equip- KAAR ENGINEERING relays, thermostats, temperature controls. ment. Palo Alto, Calif. Time -delay C. Radiotelephones, transmitters, receivers, depth sounders. H. E. Van Cleef- Jr., Dale Thompson, Harold E. Smith. R. W. Bunco, M. C. Harp, P. L. Coggeshall, C. MCCULLOUGH, INC. 301 Conner. radio direction finders. EITEL- John M Kaar, Norman C. Helwlg, Sherwood French San Bruno, Calif. HERMAN E. HELD 123 San Francisco 5 Calif. KALBFELL LABORATORIES, INC. 314 Late tube developments. San Diego, Calif. 17. (Hank) Brown, W. G. (Win) Wegener. J. L. Electrical measuring Instruments, relays, timers. Orrin n amplifiers. Micro -Miller, dec- (John) Reinarte. Herman E. Held, Ross K. Patterson, E. F. Schimhnr. BridgedT filters. plug-I ELECTRO ENGINEERING WORKS 214 HELIPOT CORP. 219 ade amplifier, logatens. South Pasadena, Calif. It. C. Kalb( ell, William G. Royce. Oakland 1S, Calif. CO., 420 Transformers, voltage regulators, power supplies, voltage Precision potentiometers. KARP METAL PRODUCTS INC. normal etc. D. IL Jones, W. Tanncek, D. C. Duncan. C. S. Mar. lrooklyn 20, N. Y. ELECTROVOICE, INC. 604 shall. Cabi nets and enclosures for electronic equipment. Buchanan, Mich. HERMETIC SEAL PRODUCTS CO. 518 HAROLD A. KITTLESON 609.10 Microphones, pickup cartridges, loudspeakers. Newark 7, N. J. Los Angeles 46, Calif. ELECTRONIC ASSOCIATES, INC. 110 Hermetic seals, glass -metal hermet sealed termi- Components and equipment of various well -known manu- Long Branch, N. J. nals, bushings, headers, plugs, and bases.bases facturers. Plotting equipment, analog computers, computer com HEWLETT- PACKARD CO. 711.12 JAMES KNIGHTS COMPANY 207 radar modifications, guided missile instru- l'alo Alto, Calif. Sandwich. Ill. ponents, ovens, frequency ments W. Noel Eldred, C. Van Rensselaer. Quartz crystals and holders, standard.

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W W 111C F;i7 MIN hfRAN.I Ft00A ELAN GROVE STREET AUDIO ENGINEERING AUGUST, 1951 a 29 SPRAGUE ELECTRIC CO. 202 o North Adams, Mesa. Capacitors, resistors, magnet wire. OAK MANUFACTURING JAMES B. LANSING SOUND, INC. 512 CO. 105 STANDARD COIL PRODUCTS CO., INC. 506 Los Angeles 39, Calif. Chicago 10, Ill. Los Angeles 32, Calif. Loudspeakers. Rotary, push-button, and elide switches, vibrators, ca- Standard TV tuner, electronic equipment and pacitors, tuners, and components. William H. Thomas, Leonard Larson. power packs. STANFORD UNIVERSITY (See adv. on Page 58) I. M. Cochrane, J. T. Driscoll, L. H. Flocken, E. J. 702 Schomhurg, R. E. Wood. Palo Alto, Calif. LASU RE CO. 416 Research projects from the electronics research labora- Los Angeles 6, Calif. OH MITE MANUFACTURING CO. 305 tory and the microwave laboratory. Record changers, three-eore solder, dial lights, capaci- Chicago 44, Ill. Resistors, rheostats, tap switches, RF chokes. CONRAD R. STRASSN ER CO. 404 -S tors. Ins Angeles F. I.aeure, Robert G. Moye. Roy S. Laird. 38, Calif. Harry A Lasure, B. Electronic parts and equipment and radiation detection LENKURT ELECTRIC CO. 121 systems. San Carlos. Calif. Conrad It. Strassner, Bernard Ep,tein, EIlard Strassner. telephone and telegraph equipment, electrical Carrier SURPRENANT MANUFACTURING CO. 412 wave filters. P Boston, 11ase. E. G. .1 Semelman. W. H. Heflin, Hall, Wire, tubing, tape, multlsonductor cables. MFG. CO. SOS LENZ ELECTRIC PERT MUTH- COLMAN da ASSOCIATES, INC. 307 -8 SYLVANIA ELECTRIC PRODUCTS, INC. 401.2 Chicago, Ill. Los Angeles 15, Calif. Wire. New York 19, N. Y. Components and equipment of various well -known manu- Germanium diodes, tubes for communications and radio - DEAN LEWIS ASSOCIATES 321 facturera. TV receivers, ruggedized tubes for industrial use. San Francisco, Calif. PERMOFLUX CORP. 522 W. G. Patterson, F. E. Gilbert, Jr., Raymond P. Radio -TV- electronic parts and equipment. Glendale. Calif. Gulon, Garland Morse, E. T. Carter, T. A. Fuller, Dean A. Lewis. Frank H. Barsl ow. Loudspeakers and transformers. Thomas Holland. LITTLEFUSE, INC. 517 John R. Molochier, L. M. Heineman, H. E. Lasater. Chicago 40. III. (See adv. on Page 41) Fuses and fuse mountings. POLYTECHNIC RESEARCH AND DEVELOP- T MENT CO. 521 Brooklyn I, N. Y. Microwave test equipment. TEKTRONIX, INC. 707.8 W. H. Fenn. Portland 7, Ore. M Cathode-ray lloscopes, wide POTTER 8, BRUMFIELD 118 on' band amplifiers. square Princeton, Ind. wave generators. McINTOSH ENGINEERING LABORATORY, Relays. TELEBEAM INDUSTRIES 17 INC. 514 Dick Brimfield, Ralph Brengie, Jim Herman,, Bud Nape, Calif. Binghamton, N. Y. Hunter. TV antennas, TV masts TV boosters. High- quality audio amplifiers. POTTER INSTRUMENT CO. 812 TETRAD COMPANY, INC. 421 (See adv. on Page 46) Great Meek, N. Y. Los Angeles 16, Calif. Electronic counters, chronographs, frequency measure Transformers and Boll components. MAGNA ELECTRONICS CO. 824 ment counters, computer components. TRANSFORMER ENGINEERS 124 Los Angeles, Calif. John J. Wild. Dudley Wright. Amplifiers, radios, electronic eomponents. Pasadena 1, Calif. Miss Jan Rise, Britten Kimball. Otto Heeger. WILLIAM J. PURDY CO. 204 -3 Transformers, chokes, filters. San Francisco 3, Calif. TRIAD TRANSFORMER MANUFACTURING MAGNECORD, INC. 513 Plekups, microphone., TV boosters, relays, oseilloNopes. CO. 423 Chicago 1, Ill. TV -FM -AM tuners, recording equipment. Los Angeles 64, Calif, Professional magnetic tape retarders. William J. Purdy, William J. Purdy, Jr., James S. Transformers and reactors, toroidal coils, TV comps C. G Barker, J. S. Boyers, R. S. MeQueen. Heaton. neat*, hermetic terminals. (See adv. en Page 39) L. W. Howard, O. D. Perry, George Clark, Dick Hast- ings, Ernest Clover, Thomas P. Walker. MARCONI INSTRUMENTS, LTD. 518 (See New York 4, N. Y. adv. on Page 38) Precision electronic measuring instrumente. R TUNG -SOL SALES CORPORATION 608 Howard Schoendure, Chet Lincoln, D. A. Pittman. Los Angeles, Calif. TungSol electron tubes. MARION ELECTRICAL INSTRUMENT CO. 213 RADCRAFT PUBLICATIONS, INC. 503A Manchester, N. H. New York 7, N. Y. THE TURNER COMPANY SO4 equip- Cedar Rapids, Iowa. Measuring instruments, meters, induction heating Radio- Electronics magazine, Gernsback library brooks. Microphone*. ment, and meter testers. Lee Logan. G. S. MARSHALL CO. 218 RADIO CORPORATION OF AMERICA (RCA Pasadena 1, Calif. Victor Division) 523 -24 Electronic tomponents and equipment of various well. Camden, N. J. U known manufacturers. El ie components, tubes, test and measuring equip- Gordon S. Marshall, Jack Hachten. ment. (See adv. on Pages 1, 8 -9) U. S. NAVY ELECTRONICS LABORATORY 703 MASTER MOBILE MOUNTS, INC. 801 San Dleeo, Calif. RADIO MAGAZINES, INC. 823 Exhibit described in official Los Angeles 36, Calif. New York 17, N. Y. program. Mobile communications antennas. AUDIO ENGINEERING magazine, AUDIO ANTHOL- U. S. ENGINEERING CO. 622 OGY, Edward Tatnall Canby broadcast transcriptions. Glendale 3, Calif. MERIT TRANSFORMER CORP. 306 James Galloway, Ladd liayetead, Cuatombuilt terminal boards. Chicago 40. Ill. C. G. McProud. Radio -TV transformers and components. RADIO RECEPTOR COMPANY, INC. 502 UNIVERSITY OF CALIFORNIA 718 New York 11, N. Y. Berkeley 4, Calif. MIDWESTERN GEOPHYSICAL LABORATORY, Selenium rectifiera. Electron refeareh projects. INC. 616 Martin Mann. Tulsa, Okla. RAYTHEON MANUFACTURING CO. 210 See official program for product listing. Newton 58, Mass. B. MILLER CO. 510.11 Radio and TV receiving tubes. cathode-ray tubes, sub- V Hollywood 28, Calif. miniature tubes, microwave tubes. H. L. Electronic components and equipment of various well - Newman. V -M CORPORATION 618 known menu facturera. E. V. ROBERTS & ASSOCIATES 309.10 Benton Harbor, Mich. Los Augeles 18, Calif. Automatic record playera. J. W. MILLER CO. 503 Shallcroas precision Instruments and components. Los Angeles, Calif. Ernest V. Roberts, Don Hagen, Frank LeBell. J. C. VAN GROSS 820.21 Radio colla. Hollywood 27. Calif. RAYMOND ROSEN ENGINEERING PRODUCTS, Components and equipment of various well -known manu MOTOROLA, INC. (Communications and INC. 312 lecturers. Electronics Division) 119 Philadelphia 4, Pa. Chicago 51, Ili. Ta lemeteri no equipment. VARIAN ASSOCIATES 413 Tweway radio and Jack Moses, Jr. San Carlos, Calif . for mobile, portable, point -te peint Klystrons, ling wave tubes, microwave measuring applications. equipment, nuclear induction apparatus.

s N W SANGAMO ELECTRIC CO. 304 Springfield, Ill. NATIONAL BUREAU OF STANDARDS 717 Mica, paper, electrolytic capacitors, time switches. WALDES KOH INOOR, INC. 215 ,18 Washington, D. C. Long Gland City, N. Y. Atomic cloca, testing standards. WALTER L. SCHOTT CO. 808 Loa Angtlee 8, Calif. Truer, retaining rings. pliers, grooving tools. H. F. Bower, John H. Degree, L. S. NATIONAL COMPANY, INC. 302 Antennas. alignment tools, electronic hardware, them I Bluth. Malden 48, Mass. cals, aceeasorles. DON C. WALLACE & WILLIAM H. WALLACE 104 Radio receivers and component parts. Robert Mueller, Jack Carter, Charle. H. Meyer. Lou Angeles 15, Calif. NAVAL RADIOLOGICAL LABORATORY SCINTILLA MAGNETO DIVISION, Bend's Radio parts and electronic equipment. Hunters Point. Calif. Aviation Corp. 208 Don Wallace. Bill Wallace. NEELY ENTERPRISES 709.10 Sidney, N. Y. WEST COAST ELECTRONIC MANUFAC- Los Angeles 46, Calif. Aircraft ignition systems, magnetos, connectors, Diesel TURERS ASSOCIATION 804 El nie and sound equipment. fuel injection equipment. Various officials of WCEMA will be present at this Noonan B. Neely, R. L. Morgan, F. B. Roessler, J. F. SERVO CORPORATION OF AMERICA 217 booth during the entire course of the Exhibit. O'Hloran, R. V. Geteen, W. R. Salon, J. C. Ingersoll, New Hyde Park, N. Y. WESTERN GOLD AND PLATINUM WORKS 114 D. Rested. R. Poucher, L. E. French, D. Kelsey. Servo mechanisms, analyzers, sub-audio generators, di- San Francisco, Calif. (See ads. on Page Si rection finding equipment, thermal radiation measuring Brazing alloys, Ceramic parts. NEWCOMB AUDIO PRODUCTS CO. 406 and detection systems. WESTERN LITHOGRAPH CO. 612 Huil)w,md 38, Calif. S. N. Howell. Los Angeles, Calif. P.A. systems, transcription players, ampliCers, radios, SIERRA ELECTRONIC CORP. 115 Wire markers. contact labels. phonogrepha. San Carlos, Calif. WESTINGHOUSE ELECTRIC CORP. 410 Robert Newcomb, Donald Warner. Test equipment and instruments. (See San Francisco 8, Calif. ads. on Page 51) W. Feidscher, Peul F. Byrne, Orm and Show. Electron). components. HAROLD L. NEWMAN 209 SIMPSON ELECTRIC CO. 203 San franciaco ASH M. WOOD CO. 810 11, Calif. Chicago, III. El Mmte, Calif. Electronic components and equipment of various well - Meters and teat equipment. known manufacturers. Electronic component,. SOLA ELECTRIC CO. J. M. 315 WORKSHOP ASSOCIATES 504A NEY CO. 103 Chicago 50, III. Needham Heights, Mass. Harth.rd, Conn. Constant voltage transformers and related products. Antennas. Precious metal alloys for electronic Instruments. L. G. Warren, J. M. Smith. NICKERSON & RUDAT 318.19 SORENSEN Sa CO., INC. 14.13 Sap Francisco, Calif. Stamford, Conn, Electronic parts and equipment. AC line voltage regulators. regulated DC power supplies, Z Dan J. RWat, E. C. Nickerson. 400 -eyere power equipment, 400 -cycle variable auto transformers. L. A. NOTT & CO. 320 ZIFFDAVIS PUBLISHING CO. 803 San Francisco 3. Calif. SPERRY GYROSCOPE CO. 211 New York 17, N. Y. Electronic components and equipment of various well- Great Neck, N. Y. known manufacturers. Radio and Television ,\'etas Klystrons and Microfilm test equipment. Leonard L. Osten, Lynn Phillips, Jr., John Payne, L. A. Noti, W. M. Noti, R. M. Mele in. W. Horn, A. Mayer, C. Rodera. Oliver Read.

30 AUDIO ENGINEERING AUGUST, 1951 Famous Products by

Hypex Projectors

Concert Series VIKIn6 Speechmaster economy speakers Reproducers

G-610 H -510 Coaxial K-210 Triaxial with Acoustic Lens Coaxial

Type M Reproducer Cabinet

Extended Range Standard Series Jensen MANUFACTURING COMPANY Division of the Muter Company lv11t011 p10w11[ 0v1171s"14 6601 S. LARAMIE AVENUE CHICAGO 38, ILLINOIS

AUDIO ENGINEERING AUGUST, 1951 31 Survey of European Sound Apparatus JOHN K. HILLIARD

A prominent audio authority reports on ten -country tour of the Continent.

IN KEEPING with his responsibilities to in many instances are required to build reason why in England be well informed LP records are on sound apparatus two models of equipment -one using not manufactured in quantities developments, the writer for the has just the European type of vacuum tube, with domestic market. Most of these completed a ten -country tour Europe, records of the other designed for American tubes. are made for export. CrystaLand earlier including England, on behalf of Altec These differences are not limited merely type magnetic Lansing. pickups are in common to a change in sockets, but in many cases use, while variable reluctance and In these countries engineers showed a other are still further complicated because of more modern pickups are available only remarkable willingness to discuss our filament voltages and other tube char- in limited numbers. mutual problems and hobbies of audio acteristics which vary greatly between At the present time England has two equipment and apparatus. This friendly the two types of tubes. In a Danish fac- transmitters radiating attitude was universal, extending a single televi- from tory, Bruel & Kjaer, of Naerum, Den- sion program on a restricted hourly the one -man development physicist to mark, many units are assembled and basis, but plans the large call for additional trans- laboratories, such as Philips' wired less vacuum tubes and sockets mitters in areas not now at Eindhoven. We were invited covered, such to their and then are completed when the coun- as Northern England and Scotland. factories and homes, met their wives try of final destination becomes known. New and more modern television and and families and joined in their discus- Add to these complexities the problems broadcasting equipment sions about the Russian is being planned frontier, the arising from power line voltages and but it will be some time before British Marshall Plan, Americans, the U. N., frequencies encountered in many Euro- broadcasting studio facilities can be and sound equipment interests. This pean markets and you will have an in- modernized method to the degree that British of surveying the resources of dication of some of the reasons why engineers have visualized. many laboratories proved to be much One of the most European sound equipment is lit- interesting observations in their more satisfactory than the correspond- erally tele- "hand made." vision reception is that the English use ence and engineering report channels, Rugged economic conditions still pre- vertically polarized which necessarily radiation as com- are incomplete and vail in both Germany and Austria, and pared to our horizontal polarization. delayed and can not completely transmit there is a six- to eight -month delay in A lasting impression of the trip was thoughts regarding avenues for new de- securing scientific text books, publica- the display velopments. of hospitality, friendship tions, and reprints. Nevertheless, in and eagerness of the engineers visited In addition to visiting the various Vienna, the Henry Radio to laboratories, and the discuss freely our technical problems. and design and manufac- Akustische and Kino Gerate, build dy- If all diplomatic relations turing groups, considerable time between coun- was namic microphones with definite im- tries in the world could be maintained spent with the professional users in the provement in diaphragm and magnetic on the same basis as those extended by ram() and recording fields. In general structure. the technical the European engineering groups, our professional audio engi- In the professional sound fields of problems in human neer is still forced relations would be to work with pre -war Europe, the advantages of the condenser simplified, and our ability designs of apparatus, which are now to establish microphone have been appreciated for world peace would be much nearer to considered obsolete in the U. S. market. a number of years and the manufacture realization. As economic recovery has progressed, of them is particularly replacement concentrated in with more modern appara- Berlin at the Georg Neumann Company, tus has been planned, but in a large under the direction New Ampex number of Dr. Hans Heyda. Chairman of cases these plans have not These microphones are used exten- yet been executed. sively, being exceeded only Since in numbers markets for audio apparatus by the 639 and 44B types of United are generally limited to the originating States manufacture. In contrast, how- country, Europe has a large number of ever, loudspeakers used for small but monitoring highly capable plants. Typical in most of the radio and recording stu- was the operation of Jakob Bohli, in dios are still limited Solothurn, to 8 -, 10 -, or 12- Switzerland. Mr. Bohli op- inch cones, often mounted in rever- erates a microphone and magnet factory. berant cabinets He, with reflectors, dif- with his three sons and daughter fusers. or other devices to improve and a very dis- few skilled mechanics, pro- tribution and quality. To overcome the duce their entire output of equipment, high frequency with beaminess of such cones. the daughter acting as office man- several models had the cones ager, interpreter, and mounted translator. The in the top or sides of the cabinets so high capabilities of the individuals in a that the number listener heard only the indirect of these small enterprises are sound. Motion picture studios seen in the ingenuity of and the- some of their atres were practically the only places in designs in order to get a satisfactory which amount modern two -way loudspeaker sys- of production without the large tems were to be found. tooling costs which are involved in With quantity the post -war problems of re- manufacturing. Every effort is building their bombed expended to avoid areas, as well as the non -uniformities their national economies, it is not sur- of finished products which often result prising Recent election of T. Kevin Mallen, from inadequate that the average European citi- general manager tooling facilities. zen has not yet been introduced since 1949, as Chair- Even when a manufacturer to home man of the Board is announced by Am- finds it music systems comparable in quality possible to cross national boundaries to pex Electric Corporation. Typical of those available in the United States. many executives in the with his product, he often finds that dif- Phonograph audio field, ferent standards reproduction is princi- Mallen also has a deep interest in the prevent uniform prod- pally with 78 r.p.m. records field of music, expressed uct design. For example, manufacturers rather than forcibly in the slower speed equipment, since it is his position as president of the Pen- not economical to replace insula Symphony Association in Red- Chief Engineer, existing Altec Lansing Corp. equipment. This is perhaps the basic wood City, Calif. 32 AUDIO ENGINEERING AUGUST, 1951 _ AIRCRAFT RADAR GEOPHYSICS RADIO

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AUDIO ENGINEERING AUGUST, 1951 33 EDWARD TATNALL CANBY* Tape Libraries WHEN TAPE FIRST APPEARED, the pos- abeyance has been the shifting develop- (a) rental library or (b) outright sale; sibility of pre -recorded tape appeared ment of the new speeds and their attendant and (c) "industrial" -radio, dinner music, with it. Due to tape's special advan- tape -to-disc techniques. That has taken a the ET market, or (d) "home" records, tages- notably the erase, re- record -patch solid three years-no time at all, when you which, if LP is any indication, also in- feature plus the portability and quality of- come down to it-and for these three years volves education and a large amount of fered for "original" or instantaneous repre -recorded tape was bound to flounder in radio. And involving all of these, one must cording -the pre -recorded concept was al- the mind, unable to find a solid resting consider the crucial matter-what shall we lowed, so to speak, to lie fallow. Other place. offer on pre -recorded tape? Popular, best- crops were cashed in on. Everything from But now the time has come. The situa- seller classical, out -of- the -way classical, home -taped baby prattle to the Private tion with regard to speeds has jelled very collectors' items, or what have you? Natu- Eye's invisible talkie -walkie (or whatever rapidly these last months. As rather fully rally in all these cases the tape library you call one of those self -powered tape predicted in this space a year ago this last builder must look at available competition midgets), from supersonic engineering January (I think it was) the 45 r.p.m. and weigh the pros and cons of comparison measurements (see the Ampex 60") to the record has now been categorized, as ideal -which vary with every situation, every plain and simple recording on tape of a for pops, for light classics, operas, for the potential use, even with various types of couple of billion hours of music for LP, not conventional best- seller classicals and for music and, above all, types of listeners. to mention a dozen or so quadrillion light- "name" performances. Columbia now makes (Compare those people who will do and years' worth of recorded broadcasts. Tape 45's up to and including such a release as pay anything for hi -fi, no matter how for permanent record and tape for transi- the complete "Carmen" -but no further. clumsy, with those who will do and pay tory record ; tape for exact transcript of The LP record, with all the interminable anything for a gadget that will flip fifty events and tape for highpowered editing - 33 vs. 45 arguments dead and forgotten, records without the touch of a human but not an inch of it was commercially pre- now has taken over 99 per cent of the clas- hand I) recorded, to sell on the open market. sical field and, moreover, has developed How come? Well, that's the point now a tremendous classical repertory and a vast Tape vs. Disc coming to an interesting preliminary issue new audience for out -of- the-way classical and trial, for time Perhaps we should consider first, before the first on any reason- music, not to mention a hundred-odd new the choice of music, the mechanical aspects ably large scale, thanks to a new offshoot classical companies, a major export music of the Audio -Video and the electrical. Granted that tape gives people, the AV Tape business in every country of Europe (poor top quality at its various levels of use (AV Libraries, to be launched around Septem- souls, they never hear a note of it) and a ber and expected Libraries will give the best that can be had to be nationally distrib- monthly output of classical music perhaps at the slower speeds -which, if you read my uted within another six months or so, and twenty times the pre -war quantity. another prospective venture description of the Ampex 400 last summer, by the enter- (Footnote : It's really funny to see the is very good.) Tape is economical prising Concertone people-"Concertape." of space, way in which RCA, making LP's right and though no more so than 33 and 45 disc. These are, to my knowledge, the first left and selling them, advertises 45's for tape libraries making Perhaps most important, tape wears, both available material everything, as at the height of the Record physically and as to sound quality, very not available in disc form, in original -qual- War-whereas Columbia, making 45's right much ity, direct re- recordings better than any ordinarily cared for (not magnetic and left in the proper divisions, keeps in- disc. (Yes, with ideal treatment a disc does "prints "), though for a long while we've credibly silent about anything but 33, and pretty well. been hearing rumors But disc treatment is seldom and tentative begin- indeed never even mentions the dreadful ideal, and tape is bound to win here, nings in this direction, and that, as any- I say, term "45" in its listings to dealers, except way, since lack of noise is inherent in the inevitably ; for pre -recorded tape in some when utterly necessary!) magnetic form has principle.) been bound to turn up sooner or The 78? Dead, except for a classical The editing and erase features are later. The problem was, and is, to de- of still trickle (Columbia scarcely makes any, now course out in pre -recorded tape, those be- termine the proper place that such tape issues LP's without 78 equivalents) and can occupy in ing among the most vital features for other the record scene; which in- the inevitable pops. Even the pops are types of tape work. volves as well the determining of the form shifting over fast to 45. They said it would it shall take-there are all Long-play is no special advantage, since sorts of possi- take ten years. LP has more or less taken care of that bilities, an infinitude of conceivable busi- And so, with the situation stabilized and - ness and distribution set -ups, a and in pre -recorded tape the really long world of on a reasonably permanent peace -time playing time (on home machines, with recorded or recordable material to draw footing, we can consider the uses of pre- upon. Where to begin? How? small reels) comes only with a sacrifice in recorded tape. Let me do so, before look- quality. With high fidelity now possible, It seems to me obvious the that main ing at Concertone's and the AV Tape Li- almost equal to the better LP's, at 7} inches thing which has held pre -recorded tape in braries' opening guns in the field. double track, tape at least can compare in The primary division of thought must length of hi -fi play with disc, though it 279 W. 4th St., New York 14, N. Y. be immediately into the basic categories, would be hard to show any marked superi-

34 AUDIO ENGINEERING AUGUST, 1951 O11. SOU

. Some months ago, I bought an AUDAX L-6 and hooked it in place of my pickup cartridge. The next day I sold it for half price to a neighbor. On all sides, since then, I have been hearing sky -high praises about AUDAX, so I again bought an L-6 POLYPHASE. But this time I hooked it up right and what a difference. It sure is mighty pleasing to my can ears. I thought it only fair to drop you a line... (from a !-r;,. Audax IOLYPIIASE rc.iroduccrs "The Standard by which Others are Judged and Valued" have won the acclaim of thousands of users everywhere -Never before decide such EAR- QUALITY, such FAITH- FUL REPRODUCTION but . . . after all the reams are written about kilocycles and other laboratory data -when the chips are that's what the man sags... down -you and only you can decide what sounds best and most pleasing to your ears. Therefore ... SEE and HEAR POLYPHASE -and you be the judge.

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AUDIO ENGINEERING AUGUST, 1951 35 ority in most applications. True. with large reels-such as Concertone's N.A.B. reels - a very long play is simple enough. But who more and more... wants it? The half hour length is pretty conclusively the most useful for a majority of purposes, only a few special problems, such as complete opera, really needing a ENGINEERS specify longer unbroken stretch. For most uses, the longer the play, the more difficult the problem of musical choice -for what is to be arbitrarily combined with what? We have enough headaches with the two -sided LP already. Which leads to the disadvantages, from the consumer's -eye point of view. Tape is clumsy to use, even in the much improved transports now in production. If the manual record player is an annoyance to plenty of lazy people, what about the threading of tape -and the annoyance of rewinding? I can hear violent arguments on both sides. Suffice it to indicate that right here is a crucial question and one very hard to pre- judge. Some people won't mind a bit; others will steer entirely clear of anything but a tape magazine, which might still be a possibility if some large company were to introduce tape plus its own special player system. That was suggested by me a couple of years ago and still stands. However, we are not concerned with such a development now. Both "Concertape" and AV tape will be straight, conventional thread -it- yourself material, to the best of my knowledge. If tape is clumsy to service, it has a far more serious disadvantage -for some people, not others. You have to begin at the beginning. You can't find a selection or passage in the middle without running tape through via the hit -or-miss system or with the "help" of some ingenious marking method which, however you look at it, cannot possibly match the utter ease of finding an LP band of music of a disc. This I know from abundant personal experience. I thoroughly dislike fussing with the stuff I have on tape, find records far easier to use. I've even had LP discs made of tapes in order to render comparisons and quick spotting of individual numbers possible. For those who always play their discs from beginning straight through without a break, tape records will be good; but for a lot of people (the people for whom LP separation bands are provided -that's most record buyers) the begin -at- the -beginning aspect will be a pain in the neck. Espe- cially when numerous items are on one tape, as is inevitable.

Players So much for the factors of doubt, pro and con. You can think of as many more, no doubt. To determine a formula for tape library operation out of all this is anything but simple. However, both Concertone and AV have approached the tape record from still another angle, that of the player. 1. People who own tape machines will be quick buyers for pre -recorded tape, if only out of curiosity and gadget- mindedness. Increases the usefulness and scope of one's machine. A sizeable audience already exists now, thanks to home tape machines already sold. 2. Tape records will stimulate the tape machine industry. Concertone makes its own. AV has already been working with machine makers and Pentron, for one, has announced a tape player for playback only, CINEMA,,ENGINEERING COMPANY minus the recording feature. (See Naw 1510 WEST VERDUGO AVENUE, BURBANK, CALIFORNIA PRODUCTS.) Ampex may well revive the 450 super -player announced last year if Eiperl ABenlr f S. Honran, ltd. 301 Cloy Slreel Son Francir, Calif., U. S. A. there is good reason. It is clearly realistic business to base a tape library development on close tie-ins

36 AUDIO ENGINEERING AUGUST, 1951 with the machines themselves and, mort over, the rest of the forming picture ma> be more easily sketched in starting frcii this concrete base. for OPTIMUM RA. PERFORMANCE Duplication Right along with the above is still an at moderate cost! other factor, a tie-in. Concertone cati ssl easily set up inexpensive batteries of it- own machines to do the basic tape copying from masters. Common power supplies, simplified or modified innards would be no trouble, given the basic mechanism. Simi- larly, Audio & Video are both agents for Specify machines and owners of similar batteries of them, used alternatively for other business. Thus both these libraries will start with most of the "plant" already available. Double -speed recording or even 4 or 8 times as fast can save time in dubbing without involving too -great engineering problems. AV, I gather, will lay in sizeable stocks of material. Concertone, I infer, plans to do more of a quick- service on -order job. Address Range Purely a matter of practical policy. Disc Public records are made, after all, on a combination of stock and special-order runs. No Audio Transformers real problem here. These famous CHICAGO "Sealed -in- Steel" AV is further along in plans, with de- Output Transformers are the choice of makers of high -quality tailed information on the AV library. The many leading and matching drivers } hour, offered in 4 ver- amplifiers. Unmatched for service in the feedback. Output set -up: all reels fully enclosed in one -piece drawn - sions, at 31 and 7} in., single and dual, Public Address range, they have a fre- are .5 from 50 to steel cases. Available in choice of two lengths to fit, on 5- and 7 -in. reels. List quency response within wire 10,000 cycles, and will deliver their full dependable constructions: with price runs from $4.50 for the slower dual leads surprisingly modest cost; with to $8.75 for the faster speed single -which rated output over this entire range. -at Line and voice coil impedances used solder lug terminals, at slightly higher means that tape is going to be a lot more Order from your electronic parts than LP disc, per playing time in the design of these output units are cost. expensive by RMA. All have distributor. Be sure to ask for CHICAGO unit. those recommended Transformers. 10' , inverse P.A. Range Audio Thanks to Ampex 400 (Concertone may tertiary windings to provide well duplicate the widened tonal range) this tape at 71 will give wide -range response, easily up to best LP standards I'd OUTPUT TRANSFORMERS Power List and noise. At 33, Catalog Typical Impedance Max. D -C say, with less distortion Secondary in Pri. Level Price quality at best is quite good, range up to No. Output Tubes Class Primary- 6 However, only the proper Pri: 5,000 ohms CT 5 or thousand. 20 $12.10 will give all of this; -many present PCO -80 P -P 6B4G's, 616's AI Sec: 600 /150/ machine 120 ma. watts 16.50 players, including expensive ones, have too PSO -80 P -P 6V6's, 6L6's AB * 16/8/4 ohms wide a gap to play the full tonal range. Pri: 10,000 ohms CT 15 10.45 Home players will sound as well as they PCO -150 P -P 6V6's, 6F6's AB Sec: 600/150/ ohms 200 ma. watts 14.85 can -the machine, not the tape being the PSO -150 P -P 6K6's ABI * 16/8;4 limiting factor. AV's 3d -in. tape, played Pri: 6,000 ohms CT 30 13.75 on a Revere, was remarkably steady, with PCO -200 P -P 6L6's B Sec: 600/150/ ma. watts 18.15 good quality through a fancy speaker. P50-200 P -P Parallel 6V6's ABZf * 16/8/4 ohms 250 Standards are high. Concertape is not of- ficially launched yet but we may expect roughly similar standards, possible if the DRIVE R, TRANSFORMERS factory Concertone machines are used with Typical Primary Max. D -C Ratio List Catalog Sec. Price supervision and control. It would seem No. Driver Tubes Impedance In Pri. P.I.11/2 likely that Concertone may indulge in $5.50 PCD -10 P -P 6N7's, 6A6's, 20,000 ohms reels to suit their larger machine. ma. 3:1 7.95 larger PSD -10 6J5's, 6C4's, etc. CT 10 There will be close tie -ins with present 5.20 PCD -25 P -P 6N7's, 6A6's, 20,000 ohms Cencertone ownership, in the Concertape 3:1 7.70 PSD -25 6J5's, 6C4's, etc. CT 25 ma. distribution. 9.35 PCD -100 P -P 6B4G's, 45's, 5,000 /10,000 5:1 13.20 PSD-100 2A3's, 616's, etc. ohms CT 100 ma. Music bias. * Has tertiary winding to provide 10% inverse feedback. t For low distortion, use fixed Aha! If you are exploding at this point to know what's available, you are a true music lover. For the present, alas, AV's Write for "NEW EQUIPMENT" TRANSFORMER Catalog library holds no interest at all for the clas- The units described above are typical of CHICAGO'S New Equipment Line sical lover. 14 preliminary rolls, two more featuring engineering that sets the transformer trend in circuit design. Get a month (in the fall) ; of the 14, all but the full facts on the complete line now. Check the features, check the quality. ene are dinner and cocktail music, safe and Check the price: see how little more these tougher, better units cost. Write sound; classical daring is represented by for your free copy of the CHICAGO New Equipment Line Catalog today. the Nutcracker Suite and the Faust ballet music. AV is not committed necessarily to this -they have here a planned experiment, hope to be able to try other musical areas. Frankly, I don't go along with this idea, but then I'm no market researcher. I feel, however, that hi -fi and LP between them have enormously changed the old rigid ideas about classical music, and even about classical best sellers. Anything may 3501 ADDISON STREET CHICAGO 18, ILLINOIS go, these days. I feel that cocktail music may have a solid and dependable initial

AUDIO ENGINEERING AUGUST, 1951 37 sale but that its limits are severe, it will not interest the large number of hi -fi people, of home record and tape machine owners, who would be enterprising enough A MPERITE to want to try tape. I may be utterly wrong. Studio Concertape, still in the planning stage Microphones and not yet actually in existence, is to the at P.A. Prices best of my knowledge to be slanted in just the opposite way, appealing fairly directly to the classical listener, with policies somewhat like many LP companies now exist- Ideal for ing. We can assume that there will also BROADCASTING be popular or light Concertape material, RECORDING but there certainly will be music for the foreground listener. PUBLIC ADDRESS\ Neither company plans to reissue music "The ultimate in micro- available on discs. A basic and wise deci- phone quality," says sion. AV's music is anonymously per- Evan Rushing, sound engineer of the Hotel formed. OK in the present area, not so good for New Yorker. classical demands. Concertape Shout right into the would have artists contracted for and an- new Amperite Micro - nounced in the usual way. phone-or stand 2 feet Both of these endeavors are in a sense away- reproduction is explosive. Both may expand suddenly or always perfect. Not wither; both are apt to shift ground as ex- affected by Models periment indicates. Concertone any climatic conditions. (partly I RBLG -200 ohms think at my suggestion) may consider si- Guaranteed to with- multaneous dual -channel stand severe "knocking RBHG -Hi -imp. records or modifi- around." cation of the same, with special head at- List $42.00 tachments for the Concertone machine, thereby achieving a wholly new type of "Kontok" Mikes reproduction so far impossible with disc Model SKH, list $12.00 records. We may be sure that, behind many Model KKH, list $18.00 a scene in many a company, these ventures will be watched with hawk -like Offe, interest. Introductory We can also be certain that under -cover Write for Special folder. Special illustrated experiments have been going on in this Offer: and 4.poge direction since the beginning of tape. Ru- mors of big- company plans of this sort reached me, and were reported, almost AMPER/TE 6mpany Inc two years ago. Anything might happen 561 BROADWAY NEW YORK I2. N Y but probably won't unless - the present rec- Canada: Atlas Radio Corp., Ltd .560 King A. W , Toronto ord business gets into a really bad hole. We shall see. RECORDS A series of 400 -cycle R. Strauss, Der Rosenkavalier. Complete Recording. Soloists of Dresden State Power Transformers Opera, Saxonian State Orchestra, Kempe. Urania LP Miniaturized URLP 201 (4) Haydn, Orfeo ed Euridice. Complete Re- cording. Soloists, Orchestra & Chorus of Voice Frequency Vienna State Opera, Swarowsky. Haydn Society LP Audio Transformers HSLP 2029 (3) Mozart, Don Giovanni. Complete Record- Both hermetically sealed to ing. Soloists, Vienna State Opera Chorus, Vienna Symphony, Swarowsky. meet MIL standards. Avail- Haydn Society LP d able from your jobber or HSLP 2030 (4) t INC. dealer. Here we are again with a glimpse at what has become one of the most significant phases of the LP revolution in many re- PRODUCTS ARE These transformers will be shown spects -complete opera. Note a number of interesting points herewith. First, these for the first time at the 7th are small -company releases again. The HANDLED BY ANNUAL PACIFIC ELECTRONIC large companies have just begun putting out complete operas, still favor the old pattern EXHIBIT and 1951 WESTERN CON- of opera "high-lights" or excerpts. The KIERULFF & CO. reason should be obvious-most large com- VENTION, I.R.E., San Francisco, panies are entangled with other speeds than LP, an enormous disadvantage LOS ANGELES August 22, in these long 23 and 24. works. The small all -LP companies still 820 W. Olympic Blvd. RI 7 -0271 have this one great and vital lead over their Write for Bulletin 451 huge rivals and they continue to exploit SAN DIEGO it- but nowhere more effectively than in the 3791 Park Blvd. Woodcrest 6275 musical colossus. LT operas of this sort the issuance of any speed other than LP is FRESNO virtually unthinkable now. (Unless, mayhap, 725 "L" Street F 24108 at 16 r.p.m. ! ) The " Rosenkavalier" recording, of which 2254 Sepulveda Blvd. I have played so far a mere half hour or Los Angeles 64, Calif. so, is a really stunning job, done on the

38 AUDIO ENGINEERING AUGUST, 1951 latest German Magnetophon equipment at MAGHECORDER 30 in. /sec. (Old -style German tape, new recording equipment.) Urania not only ex- ploits the usual favorability of European recording and its cheapness -accountable for a huge segment of existing LP repertory -but, note well, this recording comes from the East Zone of Germany. Most interesting ; for it seems that, curtain or no, the operation of an American company there in all its tremendous technical, musical and organizational detail is quite feasible; moreover, the Magnetophon recording would seem to be in no way different in quality from the best in the West Zone -suggesting that Magnetophon equipment circulates freely, somehow or other, in both zones. This is a lively, well sung performance, the sound excellent with very low distortion in the voice parts and unusual microphoning, a close -to, sharp -voice sound to the solos, yet with a volume balance that keeps the solos reasonably low in level, the orchestra loud enough, though at a greater "distance." The Vienna Haydn Society recordings, from another section of divided Europe, are presumably done on American tape at 15 in. /sec. Acoustics and mike balance count far more than any technical difference- here is a quite different mike technique, the voices at more nearly stage distance, a biggish liveness in "Don Giovanni," a some- Official Marine Corps Photo what more intimate, deader sound (ap- propriate to the musical style) in the Haydn DEPENDABILITY Opera. One must judge these differently FOR FIDELITY AND on the musical side : "Don Giovanni," a world famous opera, often done, with the ... on the beach -head very finest available singers (cf. the RCA Glyndebourne recording on 78, soon to be for the broadcast reissued on LP) is given a relatively stiff takes and stodgy performance here- though far Going in for a landing with the Marines from unlistenable. The Haydn, a rare rugged dependability. Magnecord tape recorders masterpiece virtually never heard, has no meet this requirement and provide split- second- competitors whatsoever and so must be precision recording on the beach -head. Serving all taken with thanks as good music otherwise assignments, completely unavailable, and this in spite of a over the world in vital communication certain stiffness and a few ineptitudes in Magnecorders undergo the severest conditions and the performing. These Haydn Society still continue to record with high fidelity right at large -scale rel'eases struggle manfully to the moment they are needed. avoid an ever-threatening sense of academic overweight ; a tremendous expenditure of At KIRO, Seattle, Wash., delayed programs and brains and work on the scholarly back- "on location" remotes are handled with complete ground, on outward authenticity, sometimes Magnecorders were installed. In at the expense of really top -flight artistic confidence since recreation. This is inherent, no doubt, in the field or at the station, Magnecord professional a combined scholarly and performance tape recorders are the first choice of radio engi- organization such as this one, and we can neers everywhere. easily forgive it in view of the contributions of Haydn Society to our greater msthetic pleasure. All of the above operas come FIDELITY boxed, with elaborate notes and complete FEATURES PT7 accommodates libretti in both languages ; a leisurely study 101/2" reelsand offers PT63 shown in rock of any one would take weeks to complete, 3 heads, positive mount offers three so great is the content of these offerings. timing and bushbut. FLEXIBILITY heads to erase, record, ton control. PT7 and play back to rock or console, or Remington again shown in complete In monitor from the tape console model is in its really portable while recording. the low available for port- cases, the Magnecorder The "answer" to the launching of able or rack mount. will suit every purpose. priced Remington LP was a possibly co- PT6 is available ith incidental price rise in all other records, 3 speeds (33/4", 7i ", instead of a cut. (That was, perhaps, to 15 ") if preferred. take care of the widespread 30 per cent discounts that still obtain in the large cities and via mail order on virtually all LP WRITE FOR NEW CATALOG material) The first Remingtons, as reported, were strictly a mixed bag, with some pretty squashy lemons in the lot. But since , INC. 360 N. Michigan Avenue then the company has expanded phenome- Chicago 1, III., Dept. A -8 nally and- however it is managed -I must objectively report that the new issues of the Send me latest catalog of Magnecord Equipment company, speaking generally, have (a) quite excellent recording, pressed on an adequate material with soft hiss, trade- Nama...._.___.... marked Websterlite; (b) a surprisingly interesting musical catalogue, both of stand- Addras...... __.._..___...... _.._. .._..._.._...._...... ___._ items ard works and of many unusual _...._...... _.._....Zone._.__.. State easily as enterprising as those from small Ci ty...._...._...... __..__.. companies charging standard prices, and

AUDIO ENGINEERING AUGUST, 1951 39 finally (c), though the percentage of sour notes and the like is fairly high, musical Harvey Radio Co. Elected "Jobber of the Year" performances of decidedly high value, and a general musical average not significantly below that of other LP companies. All of for the Metropolitan New York Region this though the records sell at something less than half the price of others. Is this a matter of unusually good business acumen, or, as some presumably jealous competitors might be ready to "In recognition of unfailing efforts in the interest of the Electronics suggest, is there something rotten in Denmark ? Industry at large, for ethical business practices... and That, consistent service again, my friends, is a matter into to customers." the Harvey Radio Co. has been named which Winning "Jobber it is not my business nor interest to in- of the Year" for the Metropolitan New York region by the Parta vestigate. The facts as to the records Jobber Magazine. themselves are clear enough. For the price, they are unexpectedly good This is an Award not easily given ... you have to be good to get it. Harvey and their position in the market is customers number decidedly not one to ignore. in the thousands... all over the world. They know Here are a few samples: that they can depend upon us for service, values, and the things they want when they need them. Whether you are a broadcaster, an amateur Beethoven, Symphony #3 ( "Erioca operator, a manufacturer, part of a municipality, "). or are in Civilian Austrian Symphony, Fritz Busch. Defense... you can be sure if you BUY IT FROM HARVEY. RLP 199 -21 Haydn Symphony #10I ( "Clock ") . Austrian Symphony, Fritz Busch. "JOBBER RLP 149-32 OF THE YEAH" ® MANI 'sAt.-II-CO. Busch is one of the finest Mozart- Haydn- Beethoven HARVEY RADIO_COJNC conductors and these two, while exhibiting some sour notes, are masterful .., iv!MAWS!? interpretations, notably -1* -Km:* A...., _Ha4Vaal;rl.. the Eroica scherzo . and the finale ,.r... rY s.. rr. yy,rIw.. L of the Clock. rs_,wa F.r.,.,"r.n. r,r,,,w., r..... Y M rMl... St raF s'/MrArnFS .,al> Mozart, Symphony ^," r r ^ . tn. ..,v .n".W #40 A. (*Awl w... rs.n..* manor .r-F Salzburg Festival Orch., Paul Walter so An r..... r. .x..,. {=RPn RATION RLP 149 -23 AEROs'n% Ilt (...... 1.. AA 2I e..., ..>Kgy ns, Schubert, Symphony #6 rit Alf! }wn.vA.e," Austrian Symphony, Woss. ll.( i.61 RLP 149 -30 Two lesser performances, both at least as good as average in other LP offerings, both with the quite good recording now apparently standardized for the line. O RPORA1ION P US-00.^Ow10., Virg Mt LA POINIE Bizet, Symphony in C Paris Conservatory, Allain RLP 199 -31 A clinker -and with supposedly one of the best orchestras in Europe ! It's not only as fault- ridden as any of these with lesser orchestras, but the performance is astonishingly w is IIcn.

.felra,FerS. RECORD e LIST W . a... r.. .,.. ,.., Tryy these your hi -fi outfit ;..`:"' (Note: These ' are LP', recommended as combining top 0/...".". ;'ñ,,.J technical quality with good microphoning for the type of music, plus at least reasonably good musical performance. Detailed reviews omitted for quantity coverage. Readers' opinions on the value of this type treatment -to cope with unprecedented "We are proud of your compony for achieving this recognition" Mr. Harry Kalker, floods of LP-as compared with selectively - tailed de- Soles Manager, Sprague Products Company. discussion, as in past issues, will be appreciated. Future policy is wide -open!) .. a timely recognition for the splendid jobbing job you've done" Mr. Charles - ° Outstanding over -all Golenpaul, Sales Manager, Distributor Division, Aerovox Corporation. sound. Very unusual. Modern -pretty ..you con well be proud of the outstanding job you have done' - H. F. Bersche, tough, but plenty hi -fi. Manager, Renewal Sales, Radio Corp. of America. '' Bartok, Miraculous Mandarin (ballet). .. a tribute to your fine record of service to the industry" Mr. Edward Finkel, - Bartok BRS 301. Sales Manager, JFD Manufacturing Co. Milhaud, Quartet 1912; Torino, La Oracion del .. your selection as the 'Jobber of the Year for the Metropolitan region' speaks Torero. highly for you and your staff" - Jerome E. Respess, President, La Pointe -Plascomold Polymusic PRLP 1004 Corporation. Berg, Quartet op. 3; Casella, 5 Pieces. "Your award... proves that good deeds and honest leadership are still the seeds Bartok BRS 006 Hindemith, of progress" - Lorry Epstein, Sales Manager, University Loudspeakers, Inc. Quartet #4 (Gullet) Concert Hall CHS 1086 LUxemburg 2.1500 Bartok, The Six Quartets (Willard). These ore only o few excerpts from Telephone: loners received from leading manu- Columbia ML 4278/79/80 facturers. You, toe, will like doing fr ` Bartok, Violin Sonata #1...... business with HARVEY. Columbia ML 4376 HARVEY Prokofieff, Wind Quintet op. 39; Ov. on Hebrew Themes; Swanson. Night Music. RADIO COMPANY INC. Decca DL 8511 103 Weer 43rd St., New York It, N. Y. Schoenberg, Quartet #3. Dial #4.

40 AUDIO ENGINEERING AUGUST, 1951 Modern -easier listening

Prokofieff, Piano Concerto #5; Piano Sonata #5. Period SPLP 527 Britten, Fantasy for Oboe & Strings; Quartet #1. Esoteric ES -504 "Bernstein, The Age of Anxiety (ballet). Columbia ML 4325 Barber, Symphony #2 Barber, Medea Ballet Suite Barber, Cello Concerto London LPS. 334, 333, 332 Barber, "Knoxville, Summer 1915" (sop. U orch.) Columbia ML 2174 *Villas- Lobos, Bachianas Brazilicras #1; Chorus #4, #7. Capitol P -8147 Hindemith, Symphony in E Flat (1940). Columbia ML 4387 Bartok, Rhapsody, piano & Orch; 1904; 15 Hungarian Songs; Sonatina. (Foldes). Polydcr -Vox PL 6410

Modern -lush 1110clt `Ibert, Suite Elizabethaine; Divertissement; gav -Inr Con dug Capriccio (all orch.) dynamic Orclles(r(I Westminster WL 5061 °Dohnanyi, Suite in F Sharp for Orch. Columbia ML 2172 U_f Martinu, Sinfonietta La Jolla. Britten, Les Illuminations. HEADPHONES Alco ALP 1211 Nystroem, Sinfonia del Mare. Dial #11 "I have used the Permoflux Headphones Music of Mexico (Symphonic) Decca DL 9527 on many of my programs. This has given me an opportunity to test them thoroughly Good solo piano before reporting on their performance. PermoRus High Fidelay Dynomic Headphone - I now can say that the Permoflux High Model DS -17 with Mede! °Liszt, Annees de Pelerinage: Italie (Balogh) No. 1505 Ear Cushion. Lyrichord LL 14 Fidelity Dynamic Headphones exceed in Liszt, Two Legends; Annees de Pelerinage every way any other phones I have ever used. Ire, in the music profession, (Kempf f ) who have to insist upon perfection, are perhaps more critical than other users London LLP 315 and the equipment we require must be the best. For those reasons, I mould Beethoven, Sonata op. 110; Schumann, Etudes recommend the Permoflux earphones to any one who demands the highest Symphoniques. (Casadesus i Columba ML 4388 standard of fidelity and sensitivity from such equipment." Beethoven, Sonatas op. 31, #2; op. 81a (Novaes) Unsurpassed for Broadcasting, Television and Recording Uses! Vox PL 6270 'Beethoven, Sonatas op. 109, 110 (Demus) New developments in the Permoflux Dynamic headphone design Remington RLP 199 -29 make possible the use of these units in applications heretofore not Beethoven, Sonata op. 106 (Horszowski) Vox PL 6750 covered in the electronic field. Flat frequency response of from 100 Schubert, Sonata in B flat (posth.) (Kempff) to 7000 is assured in the Permoflux High Fidelity Dynamic series LLP. London 307 and up to 4500 in the standard series. Permoflux offers the finest ° °Schumann- Brahms Recital (Sandor) television and record- Columbia ML 4375 headphones made for broadcast, tChopin, Four Scherzi (Rubinstein) ing uses as well as monitoring, audio metric work and RCA Victor LM 1132 auditory training. **Schumann, Kinderscenen; Piano Sonata #2. Send today for the new Permoflux catalog #J203 for (Blancard) Vanguard VRS 415 the latest information on Permoflux's new "Champion" 'Schumann, Carnival; Chopin, Sonata #3. line of Speakers and Dynamic Headphones. Vox PL 6710 'George Copland plays Debussy M -G -M E -526 Long) Music of Fauré (Kathleen , , London LPS 260 PERM"SOUND IN DESIGN"FLUX lBrahms, Three Intermezzi (Kempff) London LPS 205 P E R M O F L U X C O R P O R A T I O N mgachmaninoff, The 24 Preludes (Lympany) 4902 W. GRAND AVE., CHICAGO 39. ILL. 236 5. VERDUGO RD. . GLENDALE 5, CALIF London LLP 328/9 Canadian Licensee -Campbell Mfg. Company, loronta, tanod°

Key: ' some surface noise. r some flutter o overcut in spots D tends towards the percus- sive. m mechanical background noise.

AUDIO ENGINEERING AUGUST, 1951 41 quency f,. The mass in is then given by m= m, /[(f, /f,)' -1]. It is best to make SPEAKER EFFICIENCY ns, fairly close to in. In the piston range the frequency is I from page 14_1 usually low enough so that the sound pressure will not vary much with angle. speakers are fairly large (10 to 15 mils) On this basis a speaker which would asid are primarily responsible for the absorb and convert into the acoustical space factor being so low. These facts, form all power available to it would go4 combined with the greater manufactur- produce at a distance r feet in front of ing difficulties and costs of edgewound it a sound pressure level given by coils, account for the more widespread use of round-wire voice coils. Lp= L,o- 201ogtor +92.5 (7) The product aW is the magnetic Here all the radiation is assumed to be energy embraced by the actual con- confined to a hemisphere in front of the [ANSINO CORPORATION ductor in the voice coil. It can be de- speaker and infinite baffle. Le is the termined for a completely assembled sound pressure level in decibels above speaker by measuring the blocked force 0.0002 dyne /cm2 ; the unit is the dbp, produced by d.c. power in the voice coil. from analogy with dbm. Lu is the input The use of d.c. is permissible because available power level in decibels above PRODUCTS ARE of the piston range characteristics one milliwatt, and thus is in dbm. A enumerated earlier. The force F is B11s, HANDLED BY non -directional speaker of 100 per cent and the power P is I,2R,. Thus the efficiency should thus produce, with one quotient F' /P= (B1)2/R which by watt available input, an axial sound the relation developed for gap energy pressure level at ten feet of 102.5 dbp. KIERULFF & CO. is also 8traW /p. Thus A standard 12 -in. speaker will have a P z piston -range efficiency of about 2 per a W cent, so it will produce a level of 85.5 LOS ANGELES = 8tr P (6) 820 W. Olympic Blvd. RI 7 -0271 dbp under the above conditions. This If the force is measured in pounds and will be increased by directional effects the power in watts, then =1.35 x SAN DIEGO aW starting near the end of the piston range. 106F' /PC ergs. If a spring scale is 3791 Park Blvd. Woodcrest 6275 This use of free -space measurements of used for measuring the force, the read- sound pressure for calculating the total ing must be taken with the voice coil radiation in a room is justified in the FRESNO restored to and in its undeflected rest piston range, where the effect of the 725 "L" Street Fresno 24108 position so as to avoid the undesired room is small. extra contribution from the restoring It is to be noted that this simple use force of its annulus and centering mem- of efficiency in pressure level calcula- ber. Special test devices are easily made tions is not possible if the efficiency is for measuring or comparing the prod- based on ratio of motional HEIGH HO uct all'. the to total Come to the Fair! impedance. The efficiency should reflect It's THE AUDIO FAIR we mean Voice -Coil Winding two characteristics of the speaker : the ability to absorb power from the load Hotel New Yorker If the voice coil is wound with other New York City than without causing undue distortion ; and November I, 2, 3 copper, but with the same dimensions and space factor, then the relative the ability to convert the power ab- conductivity will affect the efficiency by sorbed into the acoustical form. The FOR ALL TAPE RECORDERS ! the factor C. If aluminum is the alter- "energy efficiency" calculated by mo- nate material to copper, its C is 0.64, tional resistance measurements neglects THE thus lowering the efficiency. However, the first factor. 7/ 4reltavez its density is only 0.33 that of copper, When speakers are audited properly, so a smaller total mass should result. they may be rank ordered in terms of ERASES ANY BRAND OF increasing the efficiency by the 1 /m' loudness. It will be found that this order TAPE ON ANY TYPE OF factor. It turns out that a change from is not necessarily that of the piston - REEL WITHIN SECONDS copper to aluminum will not improve the range efficiencies. This arises from the - efficiency unless Regardless of what model tape recorder you the copper voice-coil determining influence of the frequency mass is over 30 per of hove, or the brand of tape you use or the cent the total range from 1000 to 4000 cps on the loud- type of reel moving mass. In most cases this condi- -no matter how overloaded the ness. Since these frequencies are out- tape moy be -the MAGNERASER* is guar- tion will obtain only when the speaker anteed to remove all signal, and lower the is specifically designed as the low - side the piston range, no correlation is, residual noise level below that of virgin, frequency end of a two -way system. of course, to be expected. However, for unused tape. The factor (m /d') in the denomina- speakers of similar total radiation re- Gives you positive insur- tor is a measure of the surface density sponse shape the piston -range efficiency ance against failure of of the moving system. It varies (in units should be a very good indication of the Cs your erase head and Or°ntt of grams and inches) from 0.15 loudness rating. et" erase tube. Also ideal for about demagnetizing record - to 0.30 for standard speakers in the 8- to In closing, it is believed that the effi- PRÑÉSpQRIao playback and erase 18 -in. range. In the popular 10- and ciency relations discussed provide a use- heads. Easy to operate 12 -in. sizes it is about 0.25. Thus there ful means of comparing the basic per- vooaeY from any AC outlet, 100 is not too much variation in this factor. tsh e formance of direct- radiator speakers. out, v+ °UOro%° to 130 volts, 25 to 60 which leaves the gap energy as the The factors entering into the expression cycles. Weighs only 21 principal variable in the efficiency. The lbs. Size 4-in. diameter, may be measured value of ni may be estimated by first independently, or the 2 -in. high. Furnished with measuring fe, the frequency of reso- efficiency may be calculated from ob- 8 -foot line cord. served sound pressure levels. The prin- 'Trademark Reg. U. S. nance. Then add to the voice coil region Pat. Off. of the cone of the speaker a known non- cipal factors are shown to be the gap metallic mass ni,, such as modeling clay. energy and space factor, and their rela- AMPLIFIER CORP. of AMERICA which will cling to and vibrate with the tion to some design considerations has 398 BROADWAY NEW YORK 13. N. Y. cone. Measure the new resonant fre- been noted.

42 AUDIO ENGINEERING AUGUST, 1951 NEW LITERATURE

Sola Electric Co., 4633 W. 16th St.. Chi- cago 50, Ill. has recently published an interesting 24 -page two -color booklet devoted to an overall description of the Com- '14r4. .I. r,,.y.: . . pany -its history, its production facilities, lullt .. and the products It manufactures. Long known for its eminence in the constant - voltage- transformer field, Sola is to be commended for an excellent job in the `` 4 t field of public relations.

Engineering Products Department, Radio Corporation of America, Camden, N. J. has available for broadcast engineers a 4 -page illustrated brochure describing in detail the new RCA Type BTL -1A STL equipment. Well illustrated and text is strictly to the point. Must be requested on station letterhead.

Hickok Electrical Instrument Company, 10617 Dupont Ave.. Cleveland 8, Ohio, is offering free of charge a 16 -page booklet illustrating and describing the four basic methods of tube testing. Circuit diagrams and useful formulas are included. Also a catalog listing of various Hickock test instruments.

Sigma Instruments, Inc., 170 Pearl St., South Braintree (Boston 85), Mass. has available its new Catalog 51 -3, an exceptionally well -handled illustrated listing of the complete line of Sigma sensitive relays. In addition to pictures, dimen- sional drawings, and rating tables, the booklet contains a wealth of technical data to help the designer in the selection of the proper relay for any given application. The Sigma catalog is the type of industrial publication that should receive the recognition and approbation of the entire Industry. at y°tr fingertips Roberts Numbering Machine Company, 700 Jamaica Ave., Brooklyn 8, N. Y. has _ recently published a two -color leaflet dlsLat4 titled "Metal Idem ification Marking ". Of interest chiefly to companies with problems in metal stamping or embossing, the leaflet covers such diverse subjects as parts identification, embossing, engraving, and serializing. A-433A Audio-Video Recording Co., Inc., 1650 Broadway, New York 19, N. Y. has prepared a unique pocket -size rate card listing charges for every conceivable type of recording service. Both tape and disc recording dubbing duplicating, editing, and The new ALTEC two processing are included. Will be mailed -unit free upon request to anyone making use of recording media. amplifier system The Astatic Corporation, Conneaut, Engineered to the Altec standard of perfection, this new system is the finest Ohio, has recently completed preparation quality, most flexible and most practical home amplifier ever produced. The of a new phonograph cartridge directory and replacement guide. Cartridges manu- remote "fingertip" unit, finished in beautiful brushed brass, has comprehensive factured by competing companies are listed, together with recommended Astatic controls for variable bass and treble rise and droop - for the selection of the replacements. Printed on heavy stock to proper rec'ord and equalization for the of any of three withstand frequent usage, a copy may be crossover - selection obtained by writing for Form No. S -168. input channels and for volume control.

Connect this compact control unit to the "hidden" power amplifier and any Berlant Associates, 4917 W. Jefferson Blvd., Los Angeles 16 Calif. will mail on sound system will sound better. Of course, it takes an Altec speaker to fully request a new bulletin which illustrates and describes the Concertone basic mag- realize all the marvelous potential of this wonderful new amplifier system. netic -tape recorder, together with standard accessories. Included in the data are * 27 watts, less than 5% total harmonics; 20 watts, schematic diagram, frequency response curves, and list less than 2% total harmonics; less than 1/2% prices. at 15 watts!

Linde Air Products Company, 30 E. 42nd * + 0, - 1 db, 20.20,000 cycles; flat to 3 db to St., New York 17, N. Y. has assembled a 100,000 cycles! wealth of interesting data on the company's synthetic single -crystal products * Listen to this latest Altec achievement at your in a new 4 -page booklet titled "Linde nearest Synthetic Crystals for Industry ". Syn- dealer. thetic sapphire, spinel, titania, calcium tungstste, and other materials are arranged in tabular form. Properties, available forms, and uses are listed. Copy of A -333A "hidden" amplifier. the booklet will be mailed without charge.

General Electric Tube Divisions, Syra- cuse, N. Y. has re, ugly published a 107 - page pocket -size handbook listing essential characteristics of every type of vacuum tube likely to be found in a home receiver -AM, FM, or TV. Basic diagrams of 856 different tube types are shown, to- 9356 Santa Monica Blvd.. Beverly Hills. Calif. gether with performance data. The book 161 Avenue, New York, New York is priced at 35 cents and may be obtained Sixth only through General Electric and Ken - Rad tube distributors.

AUDIO ENGINEERING AUGUST, 1951 43 NEW PRODUCTS Hith- Quality Amplifier. Altec Lansing's gineered to meet exacting requirements, new amplifier for home music systems is the HP -14 uses 14 tubes and permeability of the remote- control type, consisting of a tuning to achieve sensitivity and selec- Type A -433A pre -amplifier- control unit tivity. Automatic squelch circuit may be switched in or out as desired. With squelch out maximum sensitivity is between 5 and 10 microvolts. The tuner output fed 600 ohms to 0.5 megohm.hat. Output level is proximately 3 dependent upon the load resistance. Image ratio is 1500 to 1, and audio response is flat to beyond 15,000 cps.

Tiny Rotary Switch. Developed to meet the need for miniaturization in airborne electronic equipment, a new rotary switch recently announced by Electro Develop- ment Corp., 6014 Washington Blvd., Culver City, Calif. is less than one -tenth the Model 10 is unique in the fact that all size of conventional units for performing circuits have been developed around a single tube type the 12AU7 to facilitate replacement. Selenium rectifiers provide d.c. power supply. Manufactured by Berke- and a Type A -333A power amplifier ley Scientific Corporation, 2200 Wright mounted on separate chassis. Among front - Ave., Richmond, Calif. panel controls is a three -position selector switch permitting choice of recording turnover frequencies. The user has available the correct crossover for European 78's, LP's, and records made in accordance Tandem -Type Connector. Although it wats with AES standards. Other controls pro- designed primarily for use in electric analog vide rise and droop for both treble and computers, the new Cannon Type CS con- bass, input channel selection, and volume nector is adaptable to many other applica- control. Three inputs permit use of mag- tions where tandem -type contacts are re- netic pickup, tuner, and tape reproducer. quired. Because of its low capacitance and Frequency response is virtually flat from contact resistance, the CS connector is espe- 20 to 20,000 cps. Harmonic distortion is less than 5.0 per cent at full 27 -watt output, and is less than 0.5 per cent at 15 watts. The A -433A and A -333A are available either in combination or as separate units, the A -433A being equipped with a six -foot flexible cable for interconnection similar functions. Diameter of the new with any conventional power amplifier. Edco switch is 5/8 in. and the switch Technical bulletin available from jobbers body is 3/16 in. thick. Insulation between or by writing Altec Lansing Corporation, shaft and contact arm will withstand 9356 Santa Monica Blvd., Beverly Hills, 2500 v.a.c. Contacts are of pure silver. Calif. Technical literature available from the manufacturer. cially well- suited for setting up analyzer Portable Oscilloscope. Further expand- circuits. ing its line of test equipment, Hickok The CS plug has a single silver - Electrical Instrument Co., 10617 Dupont Carrier Dialing System. Users of Type plated brass contact % in. in diameter, and H -1 Western Electric the receptacle contains two socket contacts Ave., Cleveland, Ohio, has recently intro- carrier systems may in tandem, duced the Model 380 Miniscope ", a three - convert the equipment for dial signalling insulated from each other. Bul- inch oscilloscope with frequency coverage through use of an inexpensive auxiliary letin RCS -1 will be mailed free by Cannon to 2.5 mc, and sensitivity to 0.1 r.m.s. unit now being manufactured by Lenkurt Electric Company, 3209 Humboldt St., Los Electric Co., San Carlos, Calif. In oper- Angeles 31, Calif.

Pifty -Watt Utility Amplifier. Two separately controlled 25 -watt channels are a unique feature of the newest addition to the Newcomb E Series of low -cost utility amplifiers. With inputs for three microphones and a record player, the E -50D amplifier is ideally suited for application where individual control is

volt /in. Shock mounted and housed in a moisture -proof aluminum case, the Mini - scope is an excellent instrument for mili- tary and laboratory use where portability is a factor. Size is 6 x 9 x 13% in. Com- plete technical information will be supplied by the manufacturer.

PM Tuner. Precise tuning is accomplished by means of a microammeter in the new Model HP-14 FM tuner manufactured by Collins Audio Products Co., Inc., P.O. Box 368, Westfield, N. J. En- ation the new Lenkurt auxiliary permits full -duplex carrier -frequency dial- signal- needed simultaneously for two auditori- ing pulses at 10 to 14 pps on frequencies ums with different power requirements. A not essential to the H -1 voice channels. jack is provided on the chassis to permit The equipment is exceptionally compact, interconnection with another E -50D, thus occupying less than nine inches of panel affording 100 watts of audio power from space on a standard 19 -in. rack. four separately controlled channels. Manu- factured by Newcomb Audio Products Co., 6824 Lexington Ave., Hollywood 38, Calif. Electronic Counter, Operating considerably beyond the range of standard mechanical counters, the new Berkeley Model 10 electronic counter is capable of Interlocking Connectors. Major im- counting any electrical, optical, or me- provement in design is inherent in the chanical occurrence that can be converted new, patented line of connectors recently into electrical impulses, at rates up to placed in production by Harvey Hubbell, 6000 per minute. Capacity is 9,999,999. The Inc., Bridgeport 2, Conn. Introduced as

44 AUDIO ENGINEERING AUGUST, 1951 Jhe aLJiecriminafing eventually Corne to Zeortard

BROWNING AM -FM TUNER MODEL RJ -20A Recommended for those who prefer to have all controls on one unit, this superb tuner the Hubbell Interlock, the new connector incorporates separate Bass and Treble con- has an automatic locking action which trols, Switch, Band Selector Switch, Narrow takes place when the plug is inserted in the outlet. Contacts themselves form the and Broad Band for AM tuning, and Tuning. lock, and are held under constant coil AFC may be disabled by the simple flick of a spring pressure. Release is simple, re- switch located in the rear of the chassis (for quiring only slight thumb pressure on an exposed flange. Data sheets are available fringe areas). Frequency Response-flat from from the manufacturer upon request to 15 to 15,000 cps. Department X. NET $175.17 Dynamic Headphones. Frequency response flat from 100 to 7000 cps is featured in the new high -fidelity dynamic series of headphones recently announced by Permoflux Corporation, 4900 W. Grand BROWNING HIGH -FIDELITY Ave., Chicago 39, Ill. Also stressed in design of the new phones is freedom from ir- AMPLIFIER MODEL AA -20 This broad response, medium -power amplifier has been designed specifically as a companion unit for the Browning RJ -20A Tuner. However, its superb performance makes it an ideal choice for any high quality, tuner having its own tone and volume controls. Power Rating -15 watts. Fre- quency Response -10 to 17,000 cps. NET $122.01

ritating blasts and rattles. They are exceptionally well- suited for TV studio monitoring, and already have been chosen for this purpose by a number of prominent orchestra conductors. Full information may be obtained by writing the manufacturer for Catalog J203.

Handy Card Reference. A wealth of technical informatii.u. with meaning, in all GARRARD "TRIUMPH" RECORD phases of mechanical and electrical engi- JENSEN CO -AXIAL neering, is contained in "Card- All ", a corn - CHANGER pact reference tool from General LOUDSPEAKER H -510 available The quick fool -proof action of this completely automatic record changer has made An excellent choice for those who re- it an ideal unit for custom installation as quire superb performance at a moderate well as a perfect replacement. Muting price. Built -in crossover network. Im- switch silences radio during record change. Automatic shut -off. May be had with crys- pedance -16 ohms. Power rating -21 tal pickup. watts. Wide Angle Acoustic Lens helps to provide smoothness of response. NET, less cartridge $39.00 NET with crystal pickup $44.00 NET $90.84

WRITE FOR OUR LATEST HI FI CATALOGUE

TELEPHONE: CORTLANDT 7 -0315

Design Company, 1200 Commercial Trust Building, Philadelphia 2, Penna. Made of heavy varnished cardboard to withstand constant usage, Card -All is a compact assembly of much of the technical data re- onard.. quired in general engineering practice. Miniature Insulated Terminals. Manu- facturers engaged in the miniaturization of electronic equipment will find interest in three new insulated terminals now be-

AUDIO ENGINEERING AUGUST, 1951 45 Variable Reluctance Pickup. High- quality Jack Panels. Advanced constructional fea- and low price are both featured in the new tures provide an Improved standard of mount- Clarkstan Model 204 pickup cartridge, a ve- ing convenience in the new line of jack locity- responsive mounting panels recently introduced by unit with frequency curve Audio virtually flat to above 10,000 cps. Stylus is Equipment Sales, 153 W. 33rd St., New removable York 1, N. Y. Marketed under the trade name and interchangeable, permitting AUDIO LINE, the new jack panels are avail- use of a single unit for standard, microgroove, able in 11 types-for single- and twin -ping cords, in single, double and triple rows, and with panel sixes for minimum rack space as .9"a"1 11111111Mil= 11111» s...>.. Ing marketed by Cambridge Thermionic Corporation, 464 Concord Ave., Cambridge well panels 38, Mass. The smallest of the new series, and transcription rcco- as of standard rack multiples. Type X1980XA, has an overall height of dings. Unique in de- Appearance is Improved by use of a one -piece only three -eights of an inch including sign, the 204 is housed in clear polystyrene front panel without conventional mounting terminal. Terminals are available in vari- plastic. Weight is 14 grams and overall slots. Installation is simplified by means of ous lengths with voltage breakdown rat- length is 1% in. Full technical information a concealed clamp mounting. Half -oval Plexi- ings up to 5800 volts. Additional data will will be supplied by Clarkstan Corporation, glas designation strips plug into panel without the use be supplied by the manufacturer. 11921 W. I'ico Blvd., Los Angeles 64, Calif. of screws. l'anela are available with brass or chrome jacks, or minus jacks.

Diamond -Tipped Styli Increased public demand for permanent styli is answered by the new Walco line of diamond- tipped needles for Astatic, GE, Shure, 12CA, Philco, and Webster -Elec-

A SOUND INVESTMENT FOR FINE MUSIC

'1 I

i trie cartridges. According to the manufacturer, Electrovox Co., Inc., East Orange, N. J., the new Walco styli comprise the first complete line of diamond -tipped needles available for use in standard cartridges.

Magnetic Tape Player. This new Pentron development is ideally suited for those In- stances where tape reproduction is required h without the need for recording facilities. Available with or without self- contained am- the Pentron player is capable of play - plifier,ng back tape recorded on any standard recorder at either 3% or 7% in. /sec. Model PIi -1 contains a built -in pre -amplifier and may be fed into any standard amplifier, radio

50 Watts (peak: 1001 50W -2 ... $249.50 McINTOSH, the world's most advanced amplifier, is unequalled for quality reproduction of any sound source. Highest Efficiency - over 65 %; Less Than 1% Distortion at Peak Power; Dy- namic Range: Over 70 db; Frequency Response: 20- 20,000 cps.

AE -2 Amplifier

Equalizer . . . $74.50 or TV receiver. Model PB -Al contains in addition a five -watt amplifier and 5yß -ln. PM SEND FOR CATALOG Dept. A -1 speaker. Frequency range of both models is ?lee 50 to 8000 cps at 7% in. /sec. and playing time is one hour. Flutter is less than 0.5 per cent. Weights of the two models are 4% and 7 lbs. NSi respectively. Full details will be supplied McINTOSH ENGINEERING LABORATORIES, INC. BINGHAMTO N. YT upon request by The Pentron Corporation, 221 E. Cullerton St., Chicago 16, Ill.

46 AUDIO ENGINEERING AUGUST, 1951 not run the treble boost capacitor from A check of the hearing curves will COMPENSATED CONTROL the top of the control to the arm for con- indicate that the 100 -db curve is ap- tinuously variable treble boost, because proximately flat. For a reference level, [from page 15] even though this works well as the arm it must be assumed that the maximum has been suggested that all manufactur- is lowered from the top down to the tap, volume position as at this flat position. ers use 400 cps as the bass turnover fre- treble boosting continues below the tap The nearer to this 100 -db level the quency. The curves in Fig. 4 are plotted while the bass boost stops at the tap. maximum volume of the amplifier is, the around this point. The next step is to This over -boosts treble response. closer to reality the music will sound. add treble compensation (Fig. 1). The taps can be located as desired, It is hoped that this article will indi- There are two reasons for adding this but it is found that a nice result is ob- cate a simple but complete way of de- compensation: tained by setting the top tap at one -third signing this type of control. The com- the total resistance and the bottom tap ponent values will change with different 1. To make up for the loss in highs due at one -sixth total resistance. On a 1 -meg frequencies, and are not to be to adding bass compensation. (The turnover the be fixed must be used. turnover of C, and R, causes a flattening control, these would 0.33 and 0.167 taken as values that out of the curve, but not 100 per cent. meg, respectively. The curves of Fig. 4 It is realized that when used with cer- There is always some attenuation of highs show how closely the respective bass tain amplifier curves, it may be de- above the turnover point.) and treble boosts follow the Fletcher - sirable to under- compensate or over- 2. To make up for the hearing loss in Munson curves at each tap point. compensate the volume control. highs as the volume is lowered, in accordance with the Fletcher -Munson curve. Selection of Boost Frequencies From the hearing curves we can pick FREE! WRITE TODAY out the necessary treble boost for this tap point. Since the tap is already set, the value of R, is fixed. If capacitor C, FOR YOUR 1952 is added across R the highs above the GIANT turnover point are boosted. This upper turnover frequency is the point at which Xc2 =R,. (Refer to Fig. 1.) A sug- RADIO SHACK CATALOG gested treble turnover frequency would be 2500 cps to make the turnover frequencies of bass and treble sym- ALL NEW! 192 PAGES! metrical on each side of 1000 cps. The curve can now be calculated or an OVER 15,000 PRODUCTS! oscillator and vacuum-tube voltmeter LOWEST NET PRICES a can be used to obtain the curve experi- mentally. This control can be designed as a separate unit from the amplifier, or a designer together with it as desired. If it is dean engineer signed together with the amplifier, the a purchasing agent tone controls on the amplifier should be an experimenter !- set to the "flat" position. Then with the a manufacturer you volume control in maximum volume IF YOU ARE a technician need this CATALOG position, a flat reference curve is ob- an instructor tained. Let this flat curve be equal a serviceman to the 100 -db Fletcher -Munson curve a broadcaster which is flat and add the boosts ac- a radio amateur cordingly as the midrange level is re- a custom builder duced at the different taps. If more bass compensation is needed, lower R, and increase C,, thus keeping the same turn- COMPLETE_Academy to Zephyr " - presenting all the "blue- chip" over frequency. If more treble boost is lines of instruments, components, apparatus, tools, kits, books; for desired and R, is fixed by the tap, it is all electronic and electrical development, production, radio, TV, attained by increasing C,, which turns amateurs, and hi -fi sound. over lower frequency at a and allows the DETAILED - gives pictures and full descriptions of over 15,000 curve to start rising sooner. If less items - with more technical data than ever before offered in a treble boost is desired, decrease C3, catalog of this kind. making the turnover frequency higher and the treble rise will start later. UP -TO- THE -MINUTE - includes latest information on radiation In adding the networks for the second instruments, radar, miniature and subminiature equipment. tap, the same procedure should be fol- TIME and MONEY SAVER - gives you a single, low -cost depend- lowed. Keep the same bass turnover fre- able, rapid, mail -order source for all your requirements. quency as before for the network and C, BACKED UP by the largest stocks, strongest capitalization, largest R, as in Fig. 5. - The treble boost net- most suppliers, greatest number of "blue chip" lines, lowest work is C, and R,. Referring the plant, to prices, and best delivery service anywhere in the East. sound pressure curves again, it can be seen that the treble increases as the bass increases with each successively lower FREE! MAIL THIS COUPON TODAY tap but to a lesser degree. To do this, Radio Shack Corp. Dept AE the treble turnover frequency at this 167 Washington St., Boston 8, Mass. he second tap must increased, thus al- Please send me your FREE 192 -page catalog lowing the treble to start rising later in Issue dote Sept. 1, 1951 RADIO SHACK the curve. C, does not return to the top I am a C O R P O R A T I O N of the control, but only to the tap above NAME it. It only continues the treble rise ST. and NO. 167 Washington St., Boston 8, Mass. started by the first tap. CITY ZONE. STATE One thing might be pointed out. Do

AUDIO ENGINEERING AUGUST, 1951 47 THE DEFENCE RESEARCH BOARD REQUIRES AUDIO PATENTS A SONICS SCIENTIST [front page 4J SALARY: Dependent on qualifications and experience. other end of R, is connected to the grid DUTIES: To be responsible for a sonics section with a staff of several (through a blocking capacitor) and also to junior scientists; will be required to work on fundamental sonics a capacitor leading back to the plate. problems in voice communication, speech intelligibility; measurement of hearing losses in humans and noise and blast problems. QUALIFICATIONS: A physicist or biophysicist with a Ph.D. degree; good grounding in acoustics with two or more years experience in sonics research, British subject. APPLY TO: Director of Research Personnel, Defence Research Board, Department of National Defence, "A" Building, Ottawa, Ontario. Please refer to Competition G - 8.

Fig. 3

R, and this capacitor in series form a phase-shift network. By adjusting R, the operator can adjust the phase shift and thus the phase angle at which voltage reaches the grid. A change in this phase shift will, of course, cause a shift in oscillator frequency, and in this way the vibrato rate of the instrument is variable with a single control. Frequency changes made in this manner tend to cause changes in the amplitude of the vibrato -frequency output. For a change from 4.7 to about 6.1 cps the output amplitude change is less than 6 per cent which is tolerable. Greater frequency changes, however, cause larger amplitude variations. To compensate, a part of the grid leak is made variable. R, can be ganged with R, on the same shaft so that the player can GOODMANS vary both at once, obtaining a large varia- NEIHIGH FIDELITY - 12" P. M. tion in vibrato rate without causing the amplitude change which would result in decreasing vibrato depth (amount of fre- IMF F# VO M 150 quency swing in the tone generator). This 12 -in. high fidelity unit has a twin -curvilinear dia- SPECIFICATION Variable Phase Shifter phragm (British patent No. 451754). A carefully designed mag- W. C. Morrison of Princeton, N. J., is net assembly using anisotropic Frequency Coverage material provides a total flux of 40/15,000 c.p.s. the inventor of an interesting device which 158,000 maxwells on a Ii -in. pole. The back centering device will shift the phase of an audio voltage be- is a Overall Diameter dustproof bakelised linen disk with concentric corrugations. 12 in. -31.3 cros. tween zero and almost 180 deg. continu- The combination of these features gives this precision -built in- Overall Depth ously, either statically by adjusting a con- strument an oustandingly wide coverage from 40 to 15,000 6 in. -17.6 cros. trol or dynamically in response to a mod- e.p.s. fm from bass modulation effects. An ideal high fidelity Fundamental Resonance ulating voltage. The patent number is reproducer for the record enthusiast and the connoisseur of 55 c.p.s. 2,547,767 and it is assigned to RCA. wide range musical reproduction, it gives exceptionally fine Voice Coil Diameter The circuit appears in Fig. 4. The inven- transient and frequency response. 13/4 in. -4.4 cros. tor states in the patent that he is not sure Voice Coil Impedance how it works but he gives an explanation U. S. NATIONAL SALES 15 ohms at 400 c.p.s. he believes to be correct. Input voltage WILLGOLD ELECTRONICS SALES CORP. Maximum Power Cap. is ap- 15 Watts Peak A.C. applied to the transformer primary 350 Fifth Avenue, New York, N. Y. plied between grid and in series Flux Density ground with a small bias voltage. The shield grids New England Office Chicago Office 14,000 gauss Harold A. Chamberlin Harry Halinton Co. Net Weight are connected to the B- supply though re- 31 Milk St., Boston 9, Mass. 612 N. Mich. Ave., Chicago I1, Ill. 12 lbs. 13 ozs. sistor R, across which degeneration voltage Pacific Coast Office Canadian Office 15610 grs.l appears because the shield grids are in the Perlmuth -Colman & Associates, Inc. A. C. Simmonds & Sons, Ltd. Finish -Grey Rivelling electron stream. (Ignore capacitor C for 1335 Flower St., Los Angeles, Calif. 100 Merton St., Toronto 12. Can. Enamel. the moment.) The voltage developed in this way across R, is in phase with that across Manufactured by: R,, which is the plate load. This relatively large signal across R, is applied to that G O O D M A N S I N D U S T R I E S L I I E M T D part of the shield grid which lies between W E M B L E Y MIDDLESEX E N G L A N D the screen and suppressor. 48 AUDIO ENGINEERING ' AUGUST, 1951 The screen is connected to a potentiom- tube's control grid would be r.f. and with motion -ordinarily the only effect possible eter across the bias battery, so that its po- this simple circuit an extremely large phase in following amplifiers is tremolo, a varia- tential can be varied between zero and deviation would be possible compared to tion in amplitude. Vibrato might be ob- about 7.5 volts negative. As the screen conventional methods. Effective frequency tained, however, by incorporating this phase voltage is made more negative more elec- deviation is equal to the phase shift in shifter in the amplifier and modulating the trons travel to the part of the shield grid radians times the modulating frequency. screen with a 5- to 8 -cps signal from a vi- A shift of 2 radians is possible with this brato- frequency oscillator such as those circuit, compared to about 0.5 radian with described earlier. Since resultant frequency most others ; this means that following fre- deviation is equal to the maximum phase quency multiplication to obtain the full fre- shift times the modulating frequency, a quency swing in an FM transmitter could 6-cps vibrato modulator signal would pro- be reduced by a factor of 4 or so. duce a 12-cps deviation with the shifter Another use which suggests itself is for adjusted for a 2- radian (about 115 -deg.) vibrato in either electronic musical instru- maximum shift. Deviation would, of course, ments or such devices as guitar amplifiers. vary with music -signal frequency since any When the frequency of a musical signal one value for capacitor C would produce a cannot be varied at its source -as, for in- different phase shift at different frequen- stance in an electromechanical instrument cies. A little more calculation and some like the Hammond or in a guitar whose experimentation in this line might yield player is not skilled in the necessary finger some interesting answers.

Fig. 4 fext between the control grid and screen, lowering the shield -grid voltage, and less go to Zew the plate, raising the plate voltage. At some value of screen voltage, the modulation of the electron stream by (a) the input (control -grid) voltage and (b) the voltage on the upper portion of the shield grid is :f4 STANCOR equal. Since the two are 180 deg. out of phase, the net tube output (a.c.) is zero. As the screen voltage is made more negative now the effect of the upper shield grid voltage is greater than that of the control REFERENCES grid voltage and the plate output voltage is in phase with that of the input. In practice, if control grid excitation is about .05 volt r.m.s. and the screen voltage is varied from zero to -6 volts, the output plate voltage is shifted 180 deg. At zero screen volts the plate output is about 3 volts and is the conventional 180 deg. out of phase The big new Stancor 1951 Mid -Year input. Catalog lists 441 Stancor transformers with the As screen voltage goes ...the most complete catalog line in the negative, plate output goes down to zero, industry. All transformers, including then rises again to 3 volts in phase with television components, are classified the input. and indexed so you can easily locate Now let us insert capacitor C. This is the unit you need. Each listing includes not a bypass but is chosen as a phase electrical specifications, dimensions, weight and list price. Clear illustrations shifter so that the degeneration voltage on show each mounting type in detail. the shield grid is no longer 180 deg. out of phase with the input but has some odd * * * phase relationship. Now when we vary the The 8th Edition of the Stancor Televi- screen voltage and gradually transfer con- sion Catalog and Replacement Guide trol of the electron stream from the con- provides you with quick, easy -to -read replacement information on 1511 TV trol grid to the upper part of the shield modelsand chassis made under 79 brand grid, the phase of the plate output changes names. All manufacturers are listed gradually over a range which approaches alphabetically and the models and (but does not reach) 180 degrees. chassis are listed in numerical order. A separate section lists all Stancor TV The amount of phase shift affects the components in output amplitude. The inven- transformers and related variation by part number. has found that a range of about 120 deg. tor Both of these up-to -date references are can be covered with an amplitude variation now stocked by your Stancor distrib- of about 6 db. The control function, in- utor, or write Stancor directly for your stead of being performed by a potentiometer free copies. across the bias battery, can be delegated to * * * a transformer as in Fig. 5. That gives us AUDIOPHILES -Use Stancor transformers to build the famous Williamson High Fidelity Amplifier. Cir- cuit diagrams and complete parts lists are available To Modulation in Bulletin 381 at your Stancor distributor. Screen Stancor IIE Voltage

STA NC OR Most Complete Line in the Industry

Fig. 5 CORPORATION a phase modulator when we feed modula- STANDARD TRANSFORMER tion voltage to the transformer primary. 3594 ELSTON AVENUE, CHICAGO 18, ILLINOIS In a transmitter the input frequency to the

AUDIO ENGINEERING AUGUST, 1951 49 LETTERS [from page 6J

in item 38, diamond as being 41/4 times as hard as sapphire. The term "hardness" is, by itself, meaningless, since it can refer to any one of a number of different properties of a substance such as resistance to break- age, resistance to indentation, resistance to scratching, stretching, bending, and so on. With respect to phonograph stylus usage the important property to measure is resistance to abrasive wear, and it was deter- mined many years ago that in this depart- HOW LEADING NETWORKS ment the diamond's ratio of superiority to USE CONVERTERS sapphire is 90 to 1, not 41 to 1. Confirma- Q M' of has tion this come from many tests on PRODUCTS ARE Photo above shows NBC's Tommy Bartlett relative stylus life. and Universal Recording Company engineers Mr. Weil's "Fact" No. 40 states, "There making transcriptions from STORAGE BAT- is no difference in the musical results, all HANDLED BY TERY POWER by means of Carter Fre- being equal." is quency Controlled Converter. other things This undoubt- edly true if one is speaking only of brand - Wherever 115v. line voltage is not available, new styli, but after ten hours usage under or hard to get, Carter Converters supply KIERULFF & CO. dependable AC power to make on location average conditions, the diamond tip will be recordings. Operates from storage batteries. absolutely unaltered whereas the sapphire LOS ANGELES . Used by leading networks, broadcast will have flats. It can then no longer fol- program producers. 820 W. stations, and low the groove modulations faithfully and Olympic Blvd. RI 7-0271 distortion and high -frequency losses are Recommended by Brush inevitable. It is useless to argue that by this SAN DIEGO 3791 Park Blvd. Woodcrest and Magnecord time the sapphire needle would have been 6275 changed, because (1) no longer then would One model operates both Brush and Mag- everything "everything else be equal" and FRESNO necord equipment. (2) hardly anyone changes needles as often 725 "L" Street Fresno 24108 Delivers clean 60 cycle AC power. Re- as they should be changed. Human inertia quires no filtering. is one factor, and the other is that stylus Frequency control feature compensates wear is a very gradual process, and so the for 10% input volt- accompanying musical depreciation tends age variation. Avail- able for 6. 12. 24, to escape detection. 28, 32, 64, and 115v. While the writer would agree that a DC input voltage. good is to Size 8%. x696 "x7%" sapphire stylus preferable a high. Weight only poor diamond stylus, the only factor of STILL 15% lbs. Perform- ance Guaranteed! importance-if one considers only professional- quality styli-whether the record col- AVAILABLE lector can afford the extra fifteen or twenty dollars which the diamond costs. Since in ULTRASONIC FUNDAMENTALS MAIL COUPON FOR the long run the diamond is at least ten By S. YOUNG WHITE

times as cheap as the sapphire, and since The repot Increase Igo the use of ultrasonics during CATALOG the last few years makes It atural that the web- FREE the life of a record collection hangs in the Informed sound engineer should want to learn some- balance -particularly LP's is hardly thing of the applications and potentialities of thla -it tttorkIng new liehl. Hut interest In ultruenlca U surprising that more and more phonophiles Mn confined to the sound engineer-It is of still greater importance to the hidostrlu engineer for he New Converter catalog are turning to the diamond. Ir the one who will rlsusllaa it. uses In his own illustrates entire line of Gerald Shirley, nrMYrrn Carter Rotary Convert- Elementary in character, ULTRASONIC FUN - ers for recording, TV, Televex, DAMENTALS was written originally u a eerie. of sound projection and 474 W. 238th St., magazine articles Just for the purpose of acquainting transcript on players. the novice in this field with the enormous possibilities New York 63, N. Y. of a new tool for tndnstry. It serves the double pur- SELECTOR CHART in- sound and cluded tells model to industrial tultrasonicsengineers. The list of chapter headings suit your purpose. Mail Beef, Boost, Question will indicate how It can help you. Coupon now for your copy and name of Sir : CHAPTER HEADLINES nearest Carter distributor. I wish to put in my vote to keep televi- Too Mach Audio. Opportenitles In Ultrasonics. and out of the publica- Elements of Ultrasonics. Experimental Ultra sion radio strictly Ionics. Coupllnt Ultrasonic Energy to a Load. tion. Also another pet annoyance of mine at Ultrasoncs In Ligsids. Ultrasonics In Solids. most publications is the "continued on Testing by Ultrasonics. High -Power Ultraseniu. OntiT MOTOR COMPANY Notes on Using High -Power Ultrasonics. Appli- page -" Keep your articles and advertis- cations of Ultrasonle, to Biology. Economies of ing completely separate so that articles I nags trlal Ultrason in. 2648 N. MAPLEWOOD AVE., CHICAGO 47 The applications of ultrasonics hare already ex- may be bound for future reference. tended to many industries, and a its poolbilltles Mr. Canby is still worth the price of the are explored ,they will Increase a hundredfold. To keep Carter Motor Co. abreast of its growth. engineers In all fields must from how It 264a N. NUM ewood Ave., magazine. know what they may expect ultrasonics, Chicago 47. III. Is used, how the energy Is generated, and the tech- Has anyone, other than myself, ever put niques o- applying ultrasonic treatment to many proc- Please und tuais,' 8349 with information on Frequency Control Converters, and name a counterbalance spring on a pickup arm to of nearsst distributor. equalize the force due to a tangential (off- ULTRASONIC FUNDAMENTALS By S. YOUNG WHITE pull the arm Name set) head which tends to to- 36 pages, 40 ill., 81/2 x 11, paper wards the center of the record? I found $1.75 Station or that it improved the tracking greatly. Book Division, Dept. A Coanpany G. W. Ginn, RADIO MAGAZINES. INC. 342 Madison A New York 17, N. Y. Address 411 Oneawa St., Lanikai, Oahu, T. H.

50 AUDIO ENGINEERING AUGUST, 1951 e004 leevieu/J

Piezoelectric Crystals and Their Appli- cation to Ultrasonics, by Warren P.

Mason. 508 pp. New York : D. Van Nostrand Company, Inc., $7.50. This volume of the Bell Telephone Lab- oratory Series is an excellent reference work for all engineers in the audio- acous- tics field, and should be required reading for all transducer men. The first five chapters describe crystal systems, classes and symmetries, the electrical and mechanical properties of crystals, The sound line and the determination of the properties of crystals. The methods for handling both large and small samples are discussed. In- that quality built... cluded is a list of over two hundred crystals and their degrees of coupling, which will be a guide for further development. In the second group of chapters the properties of six of the most frequently used piezoelectric crystals are discussed. Two chapters are devoted to a discussion of the ferroelectric crystals such as barium titan - ate and of the electrostrictive effect in barium titanate which is used in making the modern ceramic phonograph pickups. In the last three chapters is packed a wealth of practical information on the use of crystals in ultrasonic measurements of the physical properties of gases, liquids, and solids. The powerful mathematical tools of ten- KX-25 sor analysis are fully exploited in this work, and a thorough appendix treats this subject in detail. Thus anyone with the usual engineering background in mathematics should not hesitate to avail himself of the useful material in this book. There's a Newcomb quality amplifier for every sound need, from the low cost STANDARD E SERIES, through by C. Zwik- Sound Absorbing Materials, the superb DELUXE H SERIES, to the ker and C. W. Kosten. 171 pp. New incomparable CUSTOM K SERIES York: Elsevier Publishing Company, i I lustrated. Inc., $3.00. ware Apt G!tertatcine This contribution to the literature on acoustical materials, from the Netherlands, DEPT. T 6824 LEXINGTON AVE. is a simple straightforward presentation of HOLLYWOOD 38, CALIFORNIA the phenomena of sound absorption. The first three chapters are devoted to the development of the theory of sound absorption by various media. Following this is a discussion of the experimental determination of porosity, air resistance, and compression modulus. The chapter on measurement of normal impedance and absorption shows considerable thought and discretion in the selection NEED BACK ISSUES? of methods of measurement, from the large volume of material on the subject. Also a June 1949 July 1950 large amount of applied instrumentation is September 1949 August 1950 described. A final chapter on absorbing materials presents a thorough, if brief, com- December 1949 September 1950 parison of theoretical with practical results. January 1950 March 1951 The last quarter of the text consists of February 1950 April 1951 a chapter on resonators as sound absorbers March 1950 May 1951 and a chapter on the oblique incidence of June 1950 June 1951 sound waves on sound absorbing surfaces and resonators. Issues to December 1950 -500 each 1951 issues-35 each Frequent use of plots in the complex Z plane, the authors' lucid style, and the Payment must accompany order. treatment of normal incidence waves only in all but the last chapter have added to Circulation Dept., Audio Engineering, 342 Madison Ave., N. Y. 17, N. Y. make a valuable reference work in the field of acoustical materials.

AUDIO ENGINEERING AUGUST, 1951 51 HYCOR REALISTIC AUDIO [from page 26] voice-coils out of their magnetic gaps, with attendant uproar. We're getting better speakers all the time, but until the problem is much better solved we'll make more friends by allowing realistically for necessary speaker shortcomings. Our present speaker systems, if kept within their power and frequency capabilities, and properly baffled, will produce great satisfaction -even 'though it's within Decade - Inductor units a range of 60 to 8000 cps. Suggestions for Improvements in HYCOR DECADE - INDUCTOR units are System Design indispensable for design and experimen- So much tation work on audio filters. for the audible characteristics of systems. The weight and spatial The units are available in four ranges up requirements of some of the best quality to 10 henries. Units be used indi- may components impose difficulties. The vidually or all four may be connected in problem of interconnections among corn - series to obtain 11.11 henries in 1 milli- ponents is vexing, and indicates that it henry steps. is surely time for an industry conference Toroid coils are used to obtain high "Q", on standard plugs, at least for inputs and stability and low pickup from external outputs. Fortunately many audio houses fields. Inductance accuracy is 2 %. are willing to make up the necessary Send for bulletin D intercables, and to code them clearly. HYCOR COMPANY, INC. That doesn't help much when the healthy 11423 VANOWEN STREET, NORTH HOLLYWOOD, CALIFORNIA curiosity of the owner leads to his chang- Sunset 3 -3860 ing amplifiers or tuners or what not. manufacturers of Toroid Inductors, Decade Inductor Instruments, Wave Filters, Resistive Networks, and Precision Resistors The difficulty of arranging controls into a compact and attractive center are formidable. Figure 2 illustrates an electrically and acoustically fine instrument, marred by duplication and excessive complexity of controls. Consumers want IN ORDER TO FIND IT- the knobs to come out symmetrically, with none duplicated or useless as they are in Fig. 3. It seems to them a reason- WHY NOT BIND IT? able request. This may involve alter- ations in Your reference library of AUDIO ENGINEER- wiring and chassis arrange- ING can be up -to- the -minute by keeping your ment which non -technicians cannot be copies in an AUDIO Binder. expected to make. Some of the best APPEARANCE ... Your den, workshop ... or wherever you do your experi- amplifiers cannot, for this reason, be mentation can be kept in "apple -pie" order when all your copies of used attractively. Long steps in the AUDIO ENGINEERING are within easy reach. The deep, blue cover direction of solving this problem are will harmonize with any color scheme and ... in addition, the backbone being made in the various remote -con- will be gold- stamped with AUDIO ENGINEERING and any year you specify. trol amplifiers. Such a technique as the use of removable lock -in shafts could CONVENIENCE No more wondering what happened to last month's issue ... be or the month before ... Just reach for your Binder and no time is applied both to tuners and to ampli- lost finding the information you need ... AT ONCE. fiers, so that duplicated controls could simply be pre -set, and removed when WORKMANSHIP ... DuPont Fabricord .. - stainproof and washable ... rigid backbone with bound -in metal support . . . center channel to keep their function can be served by an ad- magazines securely in position. jacent knob on another chassis. Some COST ... For only $2.50 you can have this handsome binder for your ready tuners are so designed that removal of reference.* one, two, or more shafts, whose function e(Foreign orders add 50t per binder) may be duplicated at the amplifier, leaves a symmetrical panel. This is admirable, Audio Engineering and could and should be adopted with 342 Madison Ave., New York 17, N. Y amplifier- control panels. Most of these Enclosed find $ for Binders will be mounted in cabinets, and that fact should be considered in their design. Name Great flexibility in provisions for the connection of antennas to tuners can Address and should be provided. Tuners which - City Zone State are designed to serve also as control centers need flexible arrangements for Year Wanted 1947 1948 1949 1950. the connection of external inputs, like tape- recorders and TV sound. These

52 AUDIO ENGINEERING AUGUST, 1951 are only some of the means available to meet listeners' needs. The important thing is that these needs exist, and for the sake of survival of the profession IO4ADQUARTERS deserve attention. It seems to us that some of the problems of high -fidelity are in an admirable state of solution, and that time can be spared from them to pursue the acoustical rodents that still plague us. Among the best -solved problems in all electronics is that of the amplifier output stage. What we emphatically do not need is more good engineering talent devoted to yet another variation of the push -pull feedback power amplifier. At their best, tape and disc recording means have reached a degree of excellence that far outstrips our ability to display it acoustically. The finest of existing pick- MACNECORD PT6 -JAH up cartridges, arms, and turntables leave 1` RECORDER CI AMPLIFIER little to be desired except cost -reduction. Complete Systems from $564.00 May we not hope for concentration, ARISTOCRAT SPEAKER then, on those elements that are still Direct front radiation of high frequencies for 12" giving trouble? The biggest problem, full range driver. At least 1 full octave of added of course, is the loudspeaker system. base range at full efficiency. Mahogany finish. LIST PRICE $99.50 But there are others : record -changers, in SAME IN BLEACHED BLONDE FINISH for all the low esteem which they are LIST PRICE $106.00 held by the professional, are seriously wanted by most consumers, and their wishes deserve more than our disap- HIGH FIDELITY SYSTEMS proval. The techniques that have made ON DISPLAY separate turntable- and-arm combinations AT OUR SHOWROOMS so satisfactory, are applicable to changers. Tone -control systems designed to meet real needs, instead of to fill SOUND & RECORDING COMPANY graph -paper prettily, are not beyond 1527 CHESTNUT ST., PHILA. 2, PA. - RI. 6 -8388 reach, technically or economically. AM radio receivers are not hopeless: we have recently seen demonstrated an AM detector circuit whose distortion did not exceed 34 of 1 per cent at 99 per cent HEATHKITS modulation. A tuner with performance OFFER UNMATCHED ADVANTAGES approaching this should be available. Realism toward high-fidelity in the 'WeaA(rkdt home requires our taking the non -pro- Ri'w . TUBE CHECKER may be Ve K fessional listener seriously. It OSCILE. OPE ,r, that he cannot define exactly what he RIT wants, in our terms, but his approval $39.50 ultimately determines the success of our efforts. We hold that it is the audio And unmatched advantages in ALIGNMENT You'll professionals' deepest responsibility, not HEATHKITS most complete line GENERATOR -the test in kit form. Care- only to understand and to meet, but to KIT of equipment ful engineering and extensive labo- anticipate the needs of those whose in- $39.50 ratory testing in the development of lies in not in the each kit, coupled with the use of terest the program, give only highest quality components ELECTRONIC s equipment. More realistic and respectful you RUGGED, DEPENDABLE, and SWITCH Teatiket ACCURATE test equipment. KIT attitudes toward the listener, we are when you SIGNAL You SAVE MONEY in in because all expen- sure, will result, the end, more TRACER build your own ;19.50= factory wiring and construction realistic sound reproduction. KIT sive costs are completely eliminated ... 19.50 All kits are COMPLETE and o real pleasure to build -Every part Wear/4 necessary is furnished -and the AUDIO clear, detailed instruction manual GENERATOR makes construction easy and educe- KIT ECKER tional. (And, the finished kits are KIT truly professional in appearance.) $34.50 19.50 Order your HEATHKIT today and enjoy these tremendous advantages) O E E R B RF SIGNAL V Y O D Y GENERATOR But everybody is planning to KIT visit the Annual Convention of 19.50 The Audio Engineering Society, and The Audio Fair. Why not you? H EAT H COMPANY 1, 2, 3 - iIAIIDITESTER BENTON HARBOR 25, MICHIGAN November PIT Hotel New Yorker 13.50 New York City EXPORT AGENT: ROCKE INTERNATIONAL CORP., 13 EAST 40th STREET, NEW YORK CITY 16

AUDIO ENGINEERING AUGUST, 1951 53 LOUDSPEAKER DAMPING [from page 22] ATTENTION Tape tween speaker resonance frequency and Editors - Sound Men ft. Then above ft, where the tone - control effect is no longer bucked by a changing radiation resistance, one would expect a falling -off of response. There is NEW' TAPE SPLICER less than might be anticipated, however, because speaker cones are designed to quit functioning as rigid pistons at about "ED iTau.. this point. At any rate it can be seen that some apparent internal resistance in the amplifier is essential for flat frequency response from the usual direct- radiator speaker. This should make it clear why Price $6.50 it is that some speaker manufacturers have specified limits on the amount of feedback to be employed in amplifiers A new" tape splicing block has been developed by CBS's suitable for use with their respective speakers. It also explains why exponents famous tape editor Joel Tall and recommended by the Min- of a high damping -ratio sometimes con- nesota Mining li Mfg. Co. This new precision Dural block tradict themselves by placing a pad between amplifier and speaker. will make a PERFECT SPLICE FASTER and is less tiresome But suppose that the benefits of perfect to work with. Send for one today while still available. Mann damping are desired without reduction factured exclusively by: of low- frequency response. The speaker system must be given a big enough bite

TECH LABORATORIES, Inc. B+ R R Box 148, Palisades Park, N. J. Ra Ra (for Pentode) New York Dist. Harvey Radio Co. C Pat. applied for r R Triode) rpP+R (for

1 C C 2TRft MIDGET Fig. 10. Bass- compensation circuit for use at CONDENSER low level in preamplifier. MICROPHONE of air so that loading will remain constant down to the lowest frequency to be reproduced. Horn loading presents one Tor Precision Sound possibility. But with a horn (or horns) pains must be taken to see that the Measurements and High mouth area is adequate at frequencies well below taper cutoff. To fulfill this Quality Sound Recording condition down to 100 cps or below requires a huge installation. Horn systems designed for home use are mostly short Built to give years of service without change in on mouth area and as a result the dia- calibration. Even without dessicators, Kellogg phragm loading fluctuates violently with Midget Condenser Microphones show no detect- frequency. This may do no harm where able drift in laboratory service. Proven in use for RUGGED there is series resistance to smooth out optimum performance for more than 15 years. CONSTRUCTION the output, but, as has been shown, with EXCEPTIONAL the negative- impedance amplifier the out- CALIBRATION put will fluctuate exactly as the cone STABILITY MODEL A MODEL B loading does. Another possibility is to UNAFFECTED RESPONSE use a large number of (Referred to -59 db -55 db direct- radiator BY VARIATIONS 1 volt.' dyne/cm2) speakers. Theoretically, to be down not IN HUMIDITY more than 4 db at 60 cps would require ± 3 db from 20 to 11,000 ± 4 db from 20 to 15,000 cps FLAT TO WITHIN cps, for closed cavity wither without grille for perpen- a cone area of 5,900 sq. in. in an infinite without grille. dicular incidence in free field. wall. This would correspond with the Users Include government laboratories, staggering total of fifty -four 15 -in. universities, audio development labora- SEND FOR FULL speakers. But it is not as bad as that. By tories. sound studios and industrial plants SPECIFICATIONS TODAY! manufacturing sound equipment. WRITE DEPT. 27 -N. mounting in a corner near the ceiling or floor, one -fourth as much radiating area will suffice. By making use of ELL066SWITCHBOARD AND SUPPLY COMPANY the effective radiating area of a bass -reflex port, the Established nn number of speakers can be cut in I MIDGET CONDENSER MICROPHONE half again. As it figures out, six 15 -in. 6650 South Cicero Avenue, Chicago 38, Illinois speakers in a bass -reflex cabinet in a

54 AUDIO ENGINEERING AUGUST, 1951 corner will do very well. Since the power each speaker will be required to handle will be small, bargain- basement speakers I / / will do; the total investment can be quite úkeo,tiit Waio e small. If space or purse does not permit a cone area large enough for constant air loading, the only recourse left is to add some bass- boost, to decrease the amount of damping, or to compromise and do ...Every Ampex both. The proper turnover frequency, ft, Model 300 is for the boost and the amount of boost re- guaranteed to quired will vary with the speaker and meet published with the installation. The circuit of Fig. specifications a mild of bass -boost, 8 will give amount Model depending on the setting of Rt. The cir- Every Ampex to give cuit of Fig. 10 will give the maximum 300 is guaranteed amount that could possibly be needed and uniform performance Precision has the advantage that it may be ad- manufacture assures quick inter- justed separately from output damping. changeability of ports Model 300 However, it may be preferable to adjust is the recognized leader in the field the present bass -boost control and the of High Fidelity Recording. damping control, Rt, together until the settings that sound the best are deter- mined. If the reader is impressed by the lure of improved damping, he may still want ISO to adapt for negative impedance just for Precision Performance its novelty value. When the indicated . simple changes have been made, it will Write for complete speci- result in an amplifier whose output volt- fications today. age actually goes down when the load is removed. This phenomenon is so fasci- AMPEX ELECTRIC CORPORATION .Jiagnefic cape nating that the writer has had to demon- Redwood City California strate it for friends over and over again. RECORDERS Loudspeaker damping is an extensive W S E G R E A T R A D I O S H O subject and this article is probably not S T A N D A R D O F T H really the "last word." But it should finally lay the ghost of some old fallacies, and it does point the way to securing perfect damping by electrical means. It would be hard to ask for anything more in this direction. In the writer's opinion, it's hard to improve on perfection. AMPEX /V%Iic Tie CANNON ELECTRIC OPENS LARGE EASTERN PLANT RECORDERS Accenting its expansion to the Atlantic seaboard, Cannon Electric Company, Los for standard recording and Angeles, recently began operations in a new 10,000 -sq. ft. plant located in the East special applications Haven district of New Haven, Conn. are distributed by:

Audio & Video P R O D U C T S C O R P .

730 Fifth Ave. New York 19, N. Y.

At present the new plant will provide AMPEX MODEL 300 now available engineering and design consultation serv- delivery. ices for Cannon's eastern customers; how- for immediate ever, the company intends to add ware- housing, assembly, sub -contracting, and eventually manufacture, in order to give Wire or Telephone Collect: PLAZA 7 -3091 overnight service to the east coast, according to Robert J. Cannon, president.

AUDIO ENGINEERING AUGUST, 1951 55 Condensed Schedule For you'll find Western Electronic Event JIM LANSING SPEAKERS Marked increase in co- ordination of spon- soring organizations is evidenced in the GIVE FAITHFUL complete integration of engineering and commercial interests in the 1951 program REPRODUCTIONS of the Western I.R.E. Convention and the Annual Pacific Electronic Exhibit. The ever -increasing size and importance too! of these annual Western Electronic Events are due to close co-operation between the West Coast Electronic Manufacturers' As- sociation- sponsors of each Exhibit and Business Conference-and the local I.R.E. Sections in San Francisco and Los Angeles which alternate annually as hosts for the I.R.E. 7th Region Convention. As will be seen below, all events -engineering, business, and social-have been merged into a program which is both informative and entertaining. WEDNESDAY, AUG. 22 This magnificent high fidelity music amplifier is without peer in its popu- Morning lar price range. It incorporates a Registration built in preamplifier with inputs for Convention Papers all high fidelity pickups, and the Broadcast and Television most effective bass and treble tone controls yet developed. Hear Afternoon the DB -10 -and hear Music Exhibit Open to Visitors as the Masters Played It. Convention Papers Propagation and Optics Noise and Communication Theory Write for free literature to Dept. AS. Business Conference Government Procurement Regula- These 4 improved tions Pavédl3ogen Jim Lansing features produce TV Inspection Trip Co., INC. U. C. Radiation Laboratory and Cory °j,'- matchless tone quality Hall- Inspection Trip 663 BROADWAY, NEW YORK 12, N. Y.

1. 4" voice coil with edge wound aluminum Evening PIONEERS IN wire provides ... rigid support for the curs, Cocktail Party HIGH FIDELITY FOR OVEN 20 YEARS ilinear cone. Exhibit Open to Visitors 2. Carefully designed magnetic structure a TV Inspection Trip 3 lb. Alnico #5 permanent magnet produces higher flux densities than structures for- THURSDAY, AUG. 23 merly requiring a S lb. Alnico #5. Morning 3. Cast aluminum frame ... provides greater Registration speaker rigidity. Convention Papers 4. 4" Dural spherical center radiator...at- Vacuum Tube Applications tached directly to the voice coil cylinder... hydraulically formed to a perfect contour Afternoon .. eliminates unwanted d Ladies Fashion Luncheon distortion. Exhibit Open to Visitors Length, width and diameter of the Convention Papers voice coil magnetic gap, as well as the Linear Array Antennas magnetic force in maxwells or Circuits gausses, and the total volume of the voice coil conductor In the gap, are Business Conference vital factors affecting speaker per- Electronic Manufacturing and the formance. National Preparedness Program By using a large 4" diameter voice TV Inspection Trip coil, Jim Lansing speakers get a Inspection Trip to Eitel- McCullough tube much more favorable relationship of plant these factors than possible with a smaller diameter coil. In addition to Evening producing high flux densities, the Exhibit Open to Visitors Jim Lansing voice coil conductor is Convention Papers of sufficient volume, through mainte- The Utilization of In- ARE nance of close tolerances, to use the and Handling major portion of the magnetic force formation available in the gap. This care in TV Inspection Trip HANDLED BY manufacture assures you matchless performance. FRIDAY, AUG. 24 Years of careful research and development has kept Jim Lansing the Morning leader in fine sound. Compare the Peninsula Trip KIERULFF & CO. beautifully styled, soundly engineered Convention Papers enclosures, single speakers and com- Vacuum Tubes LOS ANGELES plete systems at your dealers today. Special Equipment 820 W. Olympic Blvd. RI 7 -0271 Afternoon Convention Luncheon SAN DIEGO Jim Lansing Exhibit Open to Visitors 3791 Park Blvd. Woodcrest 6275 \) Convention Papers Antenna Applications FRESNO SPEAKERS Computers 725 "L" Street Fresno 24108 TV Inspection Trip 2439 Fletcher Drive Evening Los Angeles 65, California Exhibit Open to Visitors

56 AUDIO ENGINEERING AUGUST, 1951 WHODATHUNKIT áoVANCE [from page k PS a pEPENDABIe leaks, and other devices, were eager and GóR APP(Ic4r anxious to promote the sale of their NW( wares in any medium that found its way 4} into the homes, shops, and factories of 4. those who might become prospective buyers. Even Wni. B. Duck was still A complete line of relays for a duckling. general circuit control, electronic, By this time there were already cer- aircraft and marine applications. magazines in circulation, Crisp action, dependable and tain wireless durable. ADVANCE offers but all of them were published in the sensitive, midget, midget tele- eastern sectors of the nation. Believing phone, keying, instrument, that the radio sun rose in New England time delay, overload, trans- and set in Hoboken, no publisher of mission line, impulse, hermetically wireless literature had ventured the risk sealed and ceramic insulated of establishing a publication on the Pa- relays. Wide variations of these 1917, that is. types for special applications. cific Coast. Until will in radio ADVANCE engineering The year became memorable supply special relays to meet history when a wild and wooly west- the most exacting requirements. erner, H. W. Dickow, then 19 years of Your inquiry will receive prompt age and for seven years prior thereto an and courteous attention. amateur and commercial wireless op- Follow the Engineers to ADVANCE. erator, risked his personal fortune of a twenty -dollar gold piece in launching Pacific Radio News. Four issues of the magazine were published in San Fran- cisco during 1917. Then came the entry of the U.S. into World War I. The staff of the magazine went to war in the wireless service of the Navy, returning ADVANIQ some three years later to resume publication. The first issue of the magazine ADVANCE ELECTRIC & RELAY CO. published in 1920 is shown on page 17. 2435 North Naomi Street * Burbank, California Although its home office was in San Francisco, only five per cent of Pacific Radio News' circulation was absorbed by westerners, and the title of the magazine was changed to Radio in keeping with its growth into a publication of na- ANNOUNCING tional stature. The change was made in Unusual Opportunities in SOUTHERN CALIFORNIA 1921 when Dickow was joined by Ar- thur H. Halloran as a business partner. Senior men with degrees and several years of proven accomplishment The two partners built Radio into one jour- may achieve further personal growth by working with some of the na- of the most influential technical laboratories. nals in the nation. It became the largest tion's outstanding scientists in the West's largest magazine publishing venture west of Chicago, and its circulation soared to a CHALLENGE AND OPPORTUNITY peak of 110.000 copies monthly. Branch for physicists and engineers in the fields of electron tubes, computers, offices were opened in New York. Chi- precision electronics, solid state, system analysis, servo -mechanisms, cago. Boston, and Los Angeles. Radio rode the crest of the sensa- radar, guided missiles, microwaves. tional boom of the twenties, but its life hung in the balance during the great HUGHES LABORATORIES OFFER depression, when its largè and note- New Air- Conditioned Buildings With the Finest Mod- worthy staff was reduced to the two ern Laboratory Facilities and Equipment. sold original partners. It was twice - Solid Long -Range Plans For a Continuing Future. first in 1935 and again in 1942. Once Intriguing Vital Defense Projects Plus a Strong Program more it gained a position of prominence For Advanced Development of New Peacetime and prestige which continued through- Products. out World War II. Company -Sponsored Program For Advanced Education. Today it is. AUDIO ENGINEERING as you know it -a title not far removed Excellent Employee Benefits. from the name of the old Audion tube to Frequent Salary Reviews. which the magazine owes its birth. Its founders are now engaged in other tech- AMPLE GOOD HOUSING AVAILABLE nical activities and its present publish- ers are confirmed in the belief that old Send Resume To magazines never die: they just find new owners who doggedly labor away under HUGHES RESEARCH AND DEVELOPMENT LABORATORIES the impression that radio- audio, that Culver City, Calif. is -is here to stay. -H.K.R.

AUDIO ENGINEERING AUGUST, 1951 57 INDUSTRIAL TRAINEE PROGRAMS ELECTRONIC and MECHANICAL ACOUSTICAL BALANCE INSPECTION -PRODUCTION -OPERATION [front page 23] CONSULTANT, RESIDENT IN and -PLANT choir, through Dr. F. Melius Christian- Services Available sen, is primarily responsible by for the Outstanding electronic and mechanical engineers impetus given serious choral music in with America. When this dean of directors Educational. Industrial and Management backgrounds began by insisting on standards in per- Write for prospectus or presentation formance and repertoire that made no Box DB1 AUDIO ENGINEERING 342 Madison .Ave.. N. Y. 17, N. Y. compromise with supposed popular taste, he accomplished two objectives: first, the shattering of an old idça that the public must be played down to if the box office is to prosper: and, second, that students must be fed music of a difficult nature only in sugar coated doses. is OVER COPIES SOLD Another choir that of Dr. Charles 9 C. Hirt, long a close associate of the late John Smaliman. In addition to his church program of some 300 singers, Dr. Hirt is Professor of Sacred Music at the University of Southern California. He is a recognized authority on Russian AND Liturgical Music. His Cathedral Choir ST/LL GO/NG STRONG! of sixty -five voices is dedicated to Christian Service through music. Many of his renditions include contemporary composers of today. Our most recent choral series is that of the famous Notre Dame Cathedral of Paris, France. This was recorded in the cathedral itself with sixty boys and fifteen men, with the audio great organ.'

Musical Education For a well rounded education in music and its acoustic values, the engineer anthology should study the following subjects to attain a better concept of music: 1. The development of musical instruments. 2. Production of sound in general. 3. The production of sound with strings, Paper cover . $2.00 reeds and brass. 4. The production of sound by air. 5. The study of harmonics and over- tones. {4 ellt Distributors write for quantity discount )11ti1""ti,P4,,""y1N"'1 w 6. The human voice. iY 1 " íYVY' i Y1r If the engineer studies these subjects as well as he does those of physics and The long awaited compilation of reprints from early issues engineering, he will be able to bridge of the gap between engineering analysis AUDIO ENGINEERING, most of which are unobtainable. and creative inspiration. The engineer must get rid of the idea that he is Contains 37 articles on the following subjects: separate and apart from the production Amplifiers of music. Music is the universal lan- Phonograph Equipment guage, and if the engineer fails to recog- Speakers Tone and Loudness Controls nize this fact, he is unwittingly con- Noise Suppressors Dividing Networks tributing a disservice to the recording industry. These articles have been of great interest to readers of AUDIO ENGINEER- Directors, on the other hand, must get ING over the past three rid of the idea that they have a corner years. Assembled in one volume, they comprise on inspiration and interpretation. If the most authoritative reference work for the audio hobbyist. what they produce doesn't get results, OUT then they must find out why, and the -CUT -MAIL TODAY - only way they can do this is through a Book Division, Dept. A9 partnership with the recording engineer. Radio Magazines, Inc. A good slogan for both would be "Is it 342 Madison Ave., New York 17, N. Y. so? Does it work? Where do I fit into the picture ?" Sirs: Enclosed is my check ij, money order for copies of As Audio Anthology. ' These are but a few of the outstanding (print choral groups we have recorded. Many of Name carefully) our colleges and universities have inspiring Address musical City organizations, and the trend to- Zone State ward serious a cappella singing is spreading throughout America.

58 AUDIO ENGINEERING AUGUST, 1951 "THE REPRESENTATIVES" of Radio Parts Manufacturers, Inc. One of the unsung heroes in the radio Davis, George W., 5127 Whittier Blvd., Los An- electronic industry is the manu- geles 22 and An- facturers' representative. Seldom seen Dempster, Burgess. 180 S. Alvarado St., Los geles 4 of equipment he by the ultimate user the Doran, Wylie M.. 1408 S. Grand Ave., Los An- sells, the "rep" does the spade work when geles 15 a new product passes the design and devel- Ealy, M. D., 633 S. La Brea Ave., Los Angeles opment stage and is ready for commercial Feldman, Henry. 400 W. Pico Blvd., Los Angeles introduction. He is the man who places Hardie, Robert M.. 1127 Wilshire Blvd., Los new amplifiers, speakers, tuners, and the Angeles 14 like on jobbers' shelves, then creates a de- Harmon, Walter S., 4057 McClung Dr., Los An- mand for them, expedites orders and de- geles 8 Hill, James J., 800 West 11th St., Los Angeles 15 livery schedules, and generally serves as Hill, Jerry T., 800 West 11th St., Los Angeles 15 throughout the long linkage trouble- shooter Hill, John T.. 800 West 11th St.. Los Angeles 15 between the manufacturer and consumer. Hitt, W. C.. 1169 S. Broadway, Los Angeles 15 Because the representative relieves the Kittleson, H. A., 7614 Melrose Ave., Los Angeles manufacturer of sales overhead he is one Knight, W. Bert. 10373 W. Pico Blvd., Los An- Mode! of the industry's great economy factors. geles 64 1401 Recorder the manufacturer Lasure, Harry A., 2216 West 11th St., Los An- installed in .liad.l Without his presence 501 Carrying Co,e would be forced to carry a large sales geles 6 payroll which, in the long run, would be Loukota, Douglas H., 1052 West 6th St., Los An- geles 17 comparison, the reflected in higher prices to the consumer. By any standard of Marsh, Joe W.. 1517 W. Pico Blvd.. Los Angeles recorder field. This, in turn would result in reduced best buy in the tape Marshall. G. S., 40 So. Los Robles Ave., Pasa- ready sales volume and a corresponding loss in Model 1401-Basic recorder dena 1 user's efficiency. It can be seen for installation. Professional manufacturing Marshank, D. N.. 672 S. Lafayette Park Pl., Los 5345.00. from this that "the rep" is truly an essen- Angeles 5 net price tial entity if sound, efficient merchandising Miller, G. B., 1540 N. Highland Ave.. Hollywood Write for Bulletin '101 is to be achieved. Neely, Norman B.. 7422 Melrose Ave.. Hollywood Resembling a professional society in Osborne. Richard E.. 1127 Wilshire Blvd., Los Monutocturea By character and intent, "The Representatives" Angeles 14 Owens. Lee H.. 2331 W. Washington Blvd., Los Berlant Associates of Radio Parts Manufacturers, Inc. is the e Angeles 18 sot r w. Jefferson sealeva. organization of these important figures. Los Angele. 16. Colitarn.o Power, Ralph D.. 767 Castelar St.. Los Angeles S It is divided into seventeen regional chap- 12 (Exec. Sec'y) ters, each of which is composed of members Reid, Ralph K., 1911 West 9th St., Los Angeles fi who cover a particular geographical area. Rissi. Al J., 1169 S. Broadway, Los Angeles 15 Listed below are members of the western Roberts. E. V., 5068 W. Washington, Los Angeles grrntli:. Rupp, V. T., 1150 W. Olympic Blvd.. Los Ange- les 15 CALFORNIA CHAPTER Saul, Howard M.. 5720 Wilshire Blvd., Los An- (.\ortlterrt CuliJnrn a S . \erada.J geles 36 Senior Memben Stone, Carl A.. 1102 S. Western Ave., Los Angeles Bellchamber, Philip A.. 212 9th St.. Oakland 7 Strassner, Conrad R., 5108 Melrose Ave.. Los Berman. Eugene L.. 1335 Market St., San Fran- Angeles 38 cisco 3 Tubergen, John B., 2232 W. 11th St., Los Angeles James P., 1234 Folson St.. San Fran- Hermann, Van Croos, J. C., 1436 N. Serrano. Hollywood 27 cisco 3 Wallace, Don C., 1206 Maple Ave., Los Angeles St., San Francisco 3 Lewis. Dean A.. 1355 Market Wallace, Wm. H., 1206 Maple Ave., Los Angeles 530 Gough St.. San Francisco 2 Logan. Les.. Wiley, Paul F., 1406 So. Grand Ave., Los Angeles Fran- Meyer, Charles N., 1355 Market St., San Wood, Ash M.. P. 0. Box 150, El Monte. Calif. cisco 3 Associate Members Moulthrop, Richard W.. 234 Ninth St.. San Fran- Boniface. R. L.. 7422 Melrose Ave., Hollywood cisco 3 Detseh, Bruce. 6100 Garfield Ave., Los Angeles 22 Newnan, Harold L., 420 Market St., San Fran- Dowers, Alfred A., 1517 W. Pico Blvd., Los An- cisco 11 geles 15 L. A.. 1061 Howard St., San Francisco 3 Nott, Ireland, Frederick, 1000 N. Seward. Hollywood Purdy, William J., 79 Ninth St. San Francisco 3 Koessler, F. B., 7422 Melrose Ave., Hollywood 46 Ross, David H., 1355 Market St., San Francisco 3 M A G N E T I C T A P E Marshank, N. J., 672 S. Lafayette Park Pl., Los Rudat, Dan J., 383 Brannan St., San Francisco 7 R E C O R D E R Angeles 5 Sinai. Arnold A., 65 Ninth St., San Francisco 3 Miller, J. W.. 5917 S. Main St.. Los Angeles 3 B E R L A N T A S S O C I A T E S Vermilya. Robert H., 1355 Market St., San Fran- Mugerl, Rudy R., 1517 W. Pico Blvd., Los Ange- cisco 3 Associate Members les 15 Is Patterson, Wm. G., 210 West 7th St., Los Angeles Hunter, John F., 1234 Folsom St., San Francisco 3 Silvey, Charles, 1816 So. Flower St., Los Angeles Kelley, J. E., c/o RCA, 1355 Market St., San Strassner, Richard A., 5108 Melrose Ave., Los HANDLED BY Francisco 3 1ovolos 38 Lewis, Dean F., 1355 Market St., San Francisco 3 Logan, Jack, 530 Gough St., San Francisco 2 PACIFIC NORTHWEST CHAPTER Logan, Jim, 530 Gough St., San Francisco 2 (U ash., U,e., l(1.,1,. 1L,,,i.. and IJ,itia KIERULFF & CO. Noti, Willard M., 1061 Howard St., San Fran- Columbia) cisco 3 Senior Members Burcham. Don H.. 917 S. W. Oak St.. Portland LOS ANGELES Purdy, Wm., Jr., 79 Ninth St., San Francisco 3 James, Ralph. 4130 First Ave., So., Seattle 4, Blvd. RI 7 -0271 Shaw, John, 1264 Folsom St., San Francisco 3 820 W. Olympic Lee, David M.. 819 Thomas Ave., Seattle 1, \\ -4. John A.. c/o Sylvania, 6450 Hollis Ave., I.m Marsh, Lloyd D., 2601 First Ave.. Seattle 1, SAN DIEGO Minthorne, Roger M.. Weatherly Bldg., Portland 3791 Park Blvd. Woodcrest 6275 LOS ANGELES CHAPTER Parsons, C. B., 119 Belmont Ave., No., Seattle. (.'O Tlll.RV (.aLIF., .IIIiO.3 .4, and Stroum, Samuel N., 610 19th Ave.. No., Seattle FRESNO southern \ , ada and Utah.) Weber, Dale G.. 234 Sherlock Bldg., Portland 4, 725 Street Fresno 24108 Senior Members Wedel, Frank, 3215 Western Ave.. Seattle 99, "L" Appleton, Harry N., 136 San Fernando Rd., Los Associate Members Angeles 31 BeLusko, Joseph V.. 819 Thomas Ave., Seattle 1, Becker, Herbert, 1406 S. Grand Ave.. Los Angeles Squibb, Raymond K.. 2601 First Ave.. Seattle 1,

AUDIO ENGINEERING AUGUST, 1951 59 IVAN is watching you

'FAN is a dyed -in- the-wool Communist. to build more and better weapons -to do needs as well. We can't allow needless 1 There are only 6 million party mem- it faster all the time. shortages to take prices skyrocketing and bers like him in all Russia, yet these Com- lower the value of our dollar. munist brass -hats enforce the iron We must use every bit of know -how and inventive skill we dictatorship of the Kremlin over 200 mil- have to improve our Sure, that means sacrifices for everybody. machines and methods lion Russians. -to turn out more But doing this double job well is the only and more for every hour we work. Only in He's sold to the hilt on Red ideas. Which sure way to stop Ivan in his tracks -and this way can we become militarily strong. means he's out to get you. He believes it's to save the freedoms which are ours and either you or him ... that the world is too But we've got to supply essential civilian which he has never known. small for both. r Ivan is working hard to beat you down. i He has a big head start. FREE... this important booklet tells you how our American System Crew Great now Right he's got you in a bad spot. How Americans developed bet- how we ran meet today's challenge -Why Ivan is afraid of only one thing. ter machines, power and skills we must expand our productive capac- to build a great nation ... Why ity... supply arms and essential civilian He fears your ability to out -produce him we have been able to produce needs, too. Read how this dynamic process works in free booklet, "The Miracle in guns, tanks, planes. constantly more per hour . How this has given us the world's of America," endorsed by representatives Frankly, he doesn't think you value your of management and labor. Send for highest living standard. your free system enough to do it ... to make free copy today! willingly the sacrifices he has squeezed out MAIL THE COUPON - None of the Russians. The Advertising Council, Inc., ä West Address But he's wrong! 15th St., Dept. B. P. New York 19, N. Y. Occupation Because you and all of us have set out

This advertisement, approved by representatives of management. labor and the public, is published in the national interest RADIO MAGAZINES, INC., 342 Madison Ave., New York 17, N. Y. TNR UTTER WI PRODUCE THI STRONGER WI OROW

60 AUDIO ENGINEERING AUGUST, 1951 WESTERN RADIO JOBBERS STEPHENS CALIFORNIA Cass Altahuler Co., 6038 Telegraph Ave., Oakland Jack C. Arbuckle, 523 E. 19th St.. Bakersfield Associated Radio Distributors, 1251 -3 Folsom St.. S.F. B raun -Knecht -Heimann Co.. 1400 16th St., S.F. HF Driver W. D. Brill 6 Co.. 198 10th St.. Oakland C. C. Brawn Co.. 61 Ninth St., S.F. California Electronic Supply, 11801 W. Pin. L.A. Channel Radio Supply Co., 434 State St.. Santa Berbera Coast Electric Co.. 744 G St., San Diego Coast Electronic Supply Co., 527 W. Main St.. Al- Unit Model 108 hambra - Fred S. Dean Co.. 969 American Ave., Long Beach Del arnett Radio Supply, 1260 Van Ness St.. Fresno Dow Radio Supply Co., 1759 E. Colorado St., Pasa- dena Dunlap Wholesale Radio CO.. 2001 "0" St., Sacra- mento Electric Supply Co.. 149 12th St.. Oakland Electronic Equip. Distributors. 1228 2nd Ave.. San Diego Electronic Supply Co.. 150 W. Green St.. Pendena Empire Electronic Supply. Inc., 37 E. Union St.. Pesa. dena Federated Percheur, Inc.. 911 S. Grand Ave.. L.A. Figart's Radio Supply CO., 6320 Commodore Stoat Dr., L.A. Gough Industries. Inc., 827 E. 1st St.. L.A. ,ßjÿ% Haggerty Radio Supply, 6826 San Fern lndo Rd., Glen- 7 %,7 dale ' Henry Radio Shop, 11240 Olympic Blvd., L.A. Hollywood Radio Supply. Inc., 5606 Hollywood Blvd., Hollywood Inland Electronic Supply. 863 Colton Ave.. San Bernar- dino Kemper Barrett Dealers Supply Co., 1850 Mission. S.F. Kaem per- Barrett Dealers Supply Co.. 1940 Ashby MODEL D -33 Streamlined Appearance Ave.. Berkeley E. M. Kemp Co.. 1115 R St., Sacramento Kierulff 5. Co.. 820 -830 W. Olympic Blvd., L.A. MICROPHONE (See Ads on Paten 38, 42, SO, 56, 59, 63) Larry Lynde Radio Supply. 853 Pine Ave.. Long Be'ch FULL VISION for both and Low Flux Leakage Mae's Radio Supply, 8320 Long Beach Bind., South- * artist gate audience Martin Distributing Co., 2303 S. Union Ave., L.A. Leo J. Meyberg Co.. Inc., 2027 S. Figueroa St.. L.A. * Attractive rich gold and black finish Improved HF Performance Miller's Radio & Television. 336 E. 8th St., Oakland Nelson Brothers Co., 630 N. Alvarado, L.A. * For Broadcast, TV, AM, FM Pacific Radio Exchange, 1407 Cahuenaa Blvd., L.A. new throat design makes this driver P acific Wholesale Co.. 116 N. 9th St., S.F. * Omnidirectional pick-up. Completely Papel Bros., 2639 E. 4th St., L.A. Id. Pasadena Radio Supply, 6110 Santa Monica Blvd., No pre -amplifier required outstanding in its ft Price, ;80.00 List. Hollywood Frank Quement. Inc.. 161 W. San Fernando St., San Write for bulletin. Jose Radio Doc, 721 5. Main St., L.A. Radio Equipment Distributors. 312 W. Pico Blvd., L.A. Radio Perte Co.. Inc., 1045 11th Ave., San Diego STEPHENS Radio Parts Sales, 5222 S. Vermont Ave., L.A. Radio Products Sales, Inc., 1501 S. Hill St., L.A. Radio Specialties Co., 1956 S. Figueroa St., L.A. Radio & Television Equipment. 709 Cherry Ave., Lang B each Radio Television Supply Co.. 341 W. 18th St., L.A. A. E. Ravenscrolt, Inc., 2320 S. Hill St., L.A. MANUFACTURING CORPORATION Sacramento Electric Supply Co.. 1219 S St.. Sacramento San Francisco Radio & Supply Co., 1282.84 Market 8538 WARNER DRIVE, CULVER CITY, CALIFORNIA St., S.F. Scott Radio Supply. 266 Alamitos Ave., Long Beach shanks & Wright. 2045 Kettner Blvd.. San Diego Shelley Radio Co.. 2008 Westwood Blvd., L.A. 5m ith 6. Crawford, 345 Mission St., S.F. Thompson Ca Holmes. Ltd., 650 Second St., S.F. united Radio & Electronics Co., 1356 5. Flower St., * Quickly and easily de- L.A. Universal Radio Supply Co.. 1729 S. Lou Angeles St., tached for hand use ADDRESS CHANGES L.A. Valley Electronic Supply Co., 1302 N. Magnolia Blvd., Convenient, light- weight Subscribers to AUDIO ENGI- B urbank * NEERING should notify our Cir- Valley Radio Supply, 716 Baker St., Station A, (weighs only 7 ounces) Bakersfield culation Department at least 5 R. V. Weatherford Co., 6919 San Fernando Rd., Glen- weeks dale in advance regarding any E. C. Wenger Co., 1450 Harrison St.. Oakland change in address. The Post Of- Western Electronic Supply Corp., 7007 Melrose Ave., L.A. fice Dept. does not forward mega - Western Radio & Television Supply Co., 1415 India uines sent to a wrong destination St.. San Diego Western Theatrical Equipment Co., 337 Golden Gate unless you pay additional postage. Ave., S.F. Wholesale Radio and Electric Supply Co.. 140 9th St., N'e can NOT duplicate copies sent S.F. to your old residence. Old and Yale Radio Electric, 6616 Sunset lvd., L.A. new addresses MUST be given. Zach Radio Supply Co., 1426 Market St., S.F. OREGON INC. Appliance Wholesalers. 600 NW 14th St.. Portland RADIO MAGAZINES, B arge It Supply. 1131 -35 SW Washington St., Portland Carlson, Hatton & Hay. Inc., 96 E. 10th St.. Eugene 342 Madison Ave. Central Distributors, 1131 -35 SW Washington St., New 17. N. Y. Portland * Mounted on model York Cressey L. Allen, 35 Commercial St., Portland Harper- Meguee, Inc., 1506 NW Irving St., Portland desk-stand MODEL "ND" Lou Johnson Co., 422 NW 8th Ave.. Pnrt land Northwest Radio Supply Co., Inc., 717 SW Akeny St., * Adjusts to any angle Portland Portland Radio Supply Co.. 1300 W. Burnside, Port- land Radio Electronics Co., 9th and Commercial, Astoria Stubbs Electric CO., 33 NW Park Ave., Portland 13! . You are buying or building Tracey 6. Co.. Inc.. 937 NW Minn. Portland United Radio Supply. Inc.. 179 W. Beh St., Eugene a TAPE RECORDER Veil G. Walker Co., 305 W. Jackson, Medford

OR. ELEMENTS WASHINGTON Associated Industries, 1752 Rainier Ave., Seattle of Columbia Electric & Mfg. Co., South 123 Wall St., SINGLE AND DUAL Spokane C L. G Radio Supply. 2502 Jefferson Ave., Tacoma don't TRACK TAPE RECORDING Garrerson Radio Supply. Second & Bell Sta., Seattle General Radio. Inc.. 100 Wall St., Seattle MODEL HB 3 and fail Harper -Meg gee. Inc., 960 Republican. Seattle FLOOR STAND dyne 1001 APPLICATIONS Kar Radio 6. Electric Co.. P.O. Box 676. Walla Walla Lay & Nord. 112 S. Second St.. Yakima Modern Theatre Supply, Inc., 2400 Third Ave., Seattle Write for free catalog printing, Pringle Radio Wholesale Co., 2516 Colby Ave., Everett and descriptive increased to 144 pages! Radio -Electric Supply Co., 2722 Second Ave.. Seattle literature Price still $1.00 postpaid Radio Products Sales Co.. 1214 First Are., Seattle Order today. Enclose dollar bill, Seattle Radio Supply, Inc.. 2117 Second Ave., Seattle Standard Sales Co., 1219 W. First Ave.. Spokane check or money order A. T. Stewart Co.. 743 Broadway, Tacoma Booklet mal led some doy Waitkus Supply Co., 110 Grand Ave., Bellingham Washington Distributors. 115 Madison Ave., Seattle AMERICAN MICROPHONE CO. Western Electronic Supply Co., 2609 First Ave., Seattle AMPLIFIER CORP. of AMERICA Wible Radio Supply Co., 907 S. Tacoma Are., Tacom 310 S. Fair Oaks Ave., Pasadena 1, Cal. 398 -2 Broadway, New York 13, N. Y. Yakima Wholesale Radio Co.. 206 5. 8th Ave.. Yakima Herb E. Zobrist Co., 2125 Westlake Ave., Seattle

AUDIO ENGINEERING AUGUST, 1951 61 L'str .loy.Keit CLASSIFIED

Rates: 10e per word per Insertion for noncemmerelI advenlsemnts; 25e per word for eommerdal adver- Regidtez tisements. Rates are net, and no discounts will be allowed. Copy must be accompanied by remIftanee In full, and must reach the New York office by the first of the month preceding the date of Issue. POSITIONS OPEN and AVAILABLE PERSONNEL may be listed here at no lilt.)\ \'NINE; 1íJ12 TUNER. hi t le used charge to industry or to members of Modernized by Browning to EJ 1 ° \ identica performance, $95 f.o.b. or best oller. Fred llar the Society. For insertion in this col- s11111, 40 Kimball Road, Watertown. Mass. umn, brief announcements should be in FOR SALE: Hi -Fl speaker system. 800 -cps the hands of the Secretary, Audio En- crossover. 15 -in. woofer and II -F horn with driver unit. Hammertone cabinet $160. III -FI gineering Society, Box F, Oceanside, Meissner 9- 1091 -B FM -AM tuner, rack- mounted, $110. Hyatt Lemoine, 323 West 75th N. Y., before the fifth of the month pre- St., New York 23, N. Y. TR 4 -8831. ceding the date of issue. TRANSCRIPTION TT OWNERS : Collec- *Positions Open Positions Wanted tion of original acetate recordings. including symphonies, Horowitz and Rubinstein l'iano works, Colman's "Tale of Two Cities," and * Sales Engineer, E. E. To cover Long others -over 200 total. Write for list, Box Island on protected basis for manufac- CK -4. AI'DIO ENGINEERING. turers' representative having outstand- LET ME improve your present amplifier to ing line of nationally advertised electronic sound like a Williamson, $49. Arthur Levine, instruments covering range from d.c. to 3405 Kossuth Ave., Bronx 67. N. Y. OL 2- microwaves. Salary, commission, ex- 6815. evenings. penses. State education, experience, past earnings. P. O. Box 569, Ridgewood, N. J. PRESTO OWNERS-- ATTENTION UN and sN overhead mechanism rebuilt for KLIPSCHORN - Closest approach to per- microgroove. 81) to 290 lines in 66 steps. De- *Engineer to design loudspeakers and sign proven 2 years in our studios. Write for fect sound reproduction at any price- Finest acoustic devices. Should have minimum of part toilers. craftsmanship -consummately styled. two years' experience in such work. This Trans -Radio Recordings, Inc., U83 Boyston Street, REBEL -Closest approach to Klipschorn at is a permanent position with a good Boston 16, Mass. a medium price. future, in a city known as an educational Both offer quality consistent with and musical center, located in western the Klipsch FOR SALE : Rek-O-Kut Challenger disc reputation; both include radiation of clean New York. Box 801, Audio Engineering. recorder; wire recorder; accessories. Ed fundamentals down to 30 cycles. Write or Cherney, 40 Ocean Parkway, Brooklyn, N. Y. visit us. * Sales Engineer wanted by leading distributor of professional tape disc WILL TRADE : Presto 6 -N, like new. for KLIPSCH AND ASSOCIATES and re- a magnecorder in good condition. Box CB -1, Hope. Arkansas Phone 995 corders, playbacks, and all accessories. Audio Engineering. Man selected will be paid for knowing his stuff. Box 802, Audio Engineerl11g. * Wanted -TV Production man who can PROFESSIONAL sell production equipment such as "rear DIRECTORY TRANSFORMERS process projection" to the right people in TV, film, and the agencies: high caliber personality. Box Sua. Audio Engineering. WITH 3 "R " S Catalog For Music Lovers C. J. LEBEL AUDIO CONSULTANT RIGHT DESIGN The music lover and the layman are given first consideration in a new Sound Development, Test, Custom Equipment, Equipment Catalog now being circulated RUGGED BUILD by Leonard Radio, Inc., 69 Cortlandt St., Complete Laboratory and Shop Facilities New York 7, N. Y. Representing consider- 133 WEST 14TH STREET able departure from the established practice NEW YORK 11, N, Y. RELIABLE RATINGS CH 3 -8082 of directing descriptive copy to technically - minded persons, the new Leonard Catalog These 3 "R "s are into built our every seldom wanders from the vocabulary of unit. The extra care that goes into a the average non -technically Tartak -inclined music -Stolle transformer or coil is a lover. Prepared by Arthur Priest, the Com- continuing guarantee of trouble -free pany's advertising manager, the new operation. We catalog solicit your inquiries on is being watched with interest by the entire Custom -Built Equipment TRANSFORMERS industry in the belief that it may point the way to new, untapped markets for audio Audio equipment. U. S. Recording Co. Output 1121 Vermont Ave., Washington 5, D. C. Power LIncoln 3 -2705 Pulse Reactors Yothisbut Noies Vibrator Concord Radio Corp., Chicago, Ill. has Special appointed Bill Cameron (W9SWO) general manager, and Gerald Levenfeld advertising & TV and merchandising manager- promotions RICHARD H. DORF are from store manager and ad manager AUDIO CONSULTANT Commercial, MIL -T27, UL, Hermetically respectively . . . Audio Is Video Product. sealed, Permafil and Special specifications Corp. has takn over quarters vacated by station WQXR at 730 Fifth Avenue, New Sound Systems Recording Installations York 19, N. Y. -space will be shared by TV Yokes & Fis -hack Transformers Audio & Video's subsidiaries Audio -Video Product Design Technical Literature Recording Co., Inc. and A -V Tape Li- braries, Inc. . Building formerly oc- 255 84th Street Tartak -Stolle Electronics, Inc. cupted by Howard Radio Company plant W. Phone New York 24, N. Y. 4 3970 So. Grand Ave., Los Angeles, Cal. in Attica, Ind, has been taken over by Schuyler -1928 Edwin I. Guthman & Company for manufacture of coils and other electronic corn-

62 AUDIO ENGINEERING AUGUST, 1951 ponents- 55,000 -sq. ft. building was chosen in keeping with government's decentrali- How linear amplifier zation program-beyond areas of critical labor shortage and the probability of air circuits are designed attack. Approaching shortage of critical materials heralded by Ettel- McCullough's ap- and constructed peal to users for return of certain types of Eimac tubes when broken or worn out, THE amplifier. discussed for salvage of parts-they even pay for 'ens . . . Berlant Associates, Los Angeles, in this volume are de- expaning with appointment of Vern May- signed to have extreme nard and John Maynard as factory repre- central values in one of several sentatives for western and south states respectively . Jensen Manu- of the pertinent char- facturing Company's t '11: tries A. Ilautsen ree leeted by the Association of Electronic acteristics: Parts and Equipment Manufacturers for n second term as the Association's repie- bandwith sentatiyc on the homed of directors for t h.. Radio Parts and Electronic Equipment for Superior Reproduction... sensitivity Shows. c it lti i t 'll iea go board member is Radio Craftsmen's John It. Cashman. for Space- saving Compactness... linearity Cinema Engineering Company, Burbank, calif. h:is appointed A. J. \tartlet' as fac- With a STEPHENS 106AX COAXIAL 2 -WAY SPEAKER constancy of gain tory rep for north central states . . The you get the True -to -life tones across the entire sound over long period, of Turner Company, Cedar Rapids. fa. adds spectrum the superb sound perfection that has made Hobert :t1. Murdock to its executive staff- - - time, etc. most will funetinti as sales nnut:tger . Hycor this speaker the monitoring choice of broadcast- Company, Inc. announces a Ppoin t ni e a t t ing stations and fine set manufacturers - without John F. Lrber as chief engineer -was formerly- with Raytheon Manufacturing sacrificing space. Co. utd RCA Institutes . . . Du Mont assembly combining a cone -type, low - VACUUM TUBE Television Network has na nled Chris .1. One compact \\ Itting :IS director- succeeds Mortimer resonant, low- frequency unit with multicellular type, \\ Lnewi who retires to become assistant cells, to the president of Allen B. Du Mont wide -angle high-frequency dispersion (eight x A 1200 cycle crossover network channels I Laboratories, Inc. Lear, Inc., Los 40° 80 °.) AMPLIFIERS Angeles, honored by alv :Ird of Doctor of to reproduce high and low tones to units designed Engineering degree to William P. Lear, board chairman ... Federal Telecommuni- them. Power rating -20 watts. Impedance -16 ohms. Edited b i cation Laboratories, Inc. has promoted Frequency response -40 to 12,000 cps. Diameter - William T. Rapp to an assistant v-ice- 131/2 Depth behind mount- GEORGE E. VALLEY, Jr. presidency- formerly assistant comptrol- 15i/1 ". Baffle opening - " - ler ... Kay Electric Company, Pine Brook, ing pone1 - 101/2". Weight -30 lbs. Recommended Assistant Professor of Physics, M.I.T. N. J. has promoted Louis A. Garten to for broadcast monitoring, motion picture sound, and - sales manager and Cyril H. Brown as his and especially-FM and record reproduction. assistant . Neely Enterprises, Holly- wood, has erected 1400 -sq. ft. single -story See your jobber or write for literature! HENRY WALLMAN addition to provide greater floor space for its expanded activities and increased per- Associate Professor of Mathematics, M.I.T. sonnel. Volume 18 in the M.I.T. STEPHENS Radiation Laboratory Series MANUFACTURING CORPORATION 733 pages illustrated $10.00 9fric&abut People 8538 WARNER DRIVE, CULVER CITY, CALIFORNIA tits book discusses. first. "linear analysis and 1 transient response" which lays the theoretical Dick Dorrance, audio veteran formerly basis for the high- fidel.ty reproduction of transient with CRS, is new director of public rela- signals. such as rectangular pulses. Although the tions for Mutual Network.... Ernie Jones, treatment is theoretical at this point, the follow- head of New York office of McManus, John ing summary shows the precise steps needed to and Adams advertising agency, trying to determine the transient response of a given net- explain away the published report that work. The practical application of these principles his hobby is "high -frequency' record- is examined for direct or "video" pulses. ing. . . . T. O. Brown advanced to super- Chapters four through seven deal with the theo- visor in sales service department of Erie retical and practical aspects of several methods of Resistor Corporation, Erie, Penn.-will be amplifying, with varying degrees of fidelity, pulse assisted by Earl R. Parser and John A. as modulated carrier frequencies as high 200 Mc/ Mayer. . . . William T. Buschman an- sec. Although the design principles are examined nounced as new merchandising coordinator chiefly from the standpoint of relatively high fre- for the Radin and TV Picture Tube Divi- in ap- quencies, they are perfectly general their sions, Sylvania Electric Products. Inc. . plication. C. J. LeBel, vice -president, Audio De- The book then takes up the examination and re- 104 vices, Inc., heartened over notable adjustment of the amplifiers previously described, sponse to his article on record critics in STEPHENS especially when they are employed as intermediate The Audio Record. Louis Zahn, di- frequency amplifiers in superheterodyne receivers. rector of research for Aerovox Corpora- Some of the innumerable ways in which inverse tion, has been appointed expert consultant feedback can be employed to stabilize the gain of on components by Research & Develop- discussed. well -known prin- Mu-R11§IC an amplifier are The ment Board for the Armed Forces . ciples of Nyquist, Bode, and others are applied John H. Hilliard, Altec Lansing chief en- particularly to circuits in which inductances do gineer, a guest of Board of Governors of not appear, and use is made of this fact to simplify New York chapter of APIS at pre -meeting MANUFACTURING CORPORATION the analysis. by Mel Sprinkle of Further chapters recount the experience at the dinner -accompanied Altec Lansing's Manhattan office. . . . Radiation Laboratory concerning the design of Louis J. Kleinklans appointed chief engi- rugged and reliable direct -coupled amplifiers, no neer of R-itNlt, New York, to succeed the particular emphasis being placed upon extreme late Russell D. Valentine -Athan Commas sensitivity. named engineer -in- charge of FM and AM PRODUCTS ARE transmitters. Check these 14 valuable chapters: Roger B. Yepson upped to manager of marketing research for the Tube Divisions HANDLED BY 1. Linear-Circuit Analysis and Transient Response of General Electric. . Ken Hamilton, 2. High- Fidelity Pulse Amplifiers formerly with Capehart, named to direct 3. Pulse Amplifiers of Large Dynamic Range promotional sales activities for Marshank 4. Synchronous and Staggered Single -Tuned Sales Co., Los Angeles. . Jack Coles, High- Frequency Bandpass Amplifiers many years with the Bell System. has KIERULFF & CO. 5. Double -Tuned Circuits Joined J. T. Hill Sales Co., Los Angeles, 6. High -Frequency Feedback Amplifiers as office manager. Read Hamilton 7. Bandpass Amplifiers: Pulse Response and Gen- Wight, who master- minded World Broad- LOS ANGELES eral Considerations casting System's Chicago office into world- 8. Amplifier Measurement and Testing wide prominence, and who is now radio - 820 W. Olympic Blvd. RI 7 -0271 9. Low-Frequency Amplifiers with Stabilized Gain TV head of J. M. Mathes Advertising 10. Low-Frequency Feedback Amplifiers Agency, adding new Garard changer and I1. Direct -Coupled Amplifiers high -quality pickups to custom -built am- SAN DIEGO 12. Amplifier Sensitivity plifier and speaker system. . . 3791 Park Blvd. Woodcrest 13. Minimal Noise Circuits Jack Simon, director of Terminal Radio 6275 14. Measurement of Noise Figure Corporation's Sound department, reports rising curve of audio equipment sales in TV homes -says music lovers want music, FRESNO RADIO MAGAZINES, INC. TV or no TV. .. Crump Smith. ad chief 725 "L" Street Fresno 24108 for Federal Tel and Tel, is industry's only "reverse commuter" -lives in Manhattan 342 Madison Avenue and travels daily to Federal plant in Clif- ton, N. J.. . Luci Turner, eE production New York 17, N. Y. manager, on vacation -Help!

AUDIO ENGINEERING AUGUST, 1951 63 ADVERTISING PARTRIDGE THE AUDIO TRANSFORMERS INDEX that pass ALL tests

Time, no less than test, has proved Partridge Audio Advance Electric & Relay Co. 57 Transformers to be the most effi- Air -Tone Sound & Recording Co. 53 cient and reliable in the world. HIGH -FIDELITY H. T. GREETINGS Altec Lansing Corp. 43 American Microphone Co. 61 * WILLIAMSON Output TRANS- TO THE WEST COAST Amperite Co., Inc. 38 FORMERS, of which there is no U. S. Ampex Electric Corp. 55 equivalent (vide "Audio Engineering" Nov. 1949) built to the original specification, To all our customers and friends in Wash- Amplifier Corp. of America 42, 61 comes to you for $21.00, mail and in- ington, Oregon and California, greetings. The Arnold Engineering Co., The 3 6,000 miles will prevent our being surance paid. intervening Audak Co. 35 at the Annual Pacific Electronic Exhibit to greet Audio Devices, Inc. Cover 2 * PARTRIDGE CFB 20 Watt output you personally, but we shall be there in the type, accepted as without rival. Series leak- minds of those who get our news letters and buy Audio & Video Products Corp. 55 age induct. 10 m.H; primary shunt induct. products. Bell our Telephone Laboratories 12 130 H, with 'C' core construction and Berlant Associates 59 hermetically sealed-to you for $30.00, We have a lot of very satisfied users of the Bogen Co., Inc., David 56 mail and insurance paid. 215 Speaker on the West Coast, as well as in British Industries Corp. 11 all other parts of the U. S. Each and every one of those customers exhibited three character- Brook Electronics, Inc. 64 Fullest data, including square wave tests, dis- istics: curiosity as to what we were up to; Cannon Electric Co. 6 tortion curves etc., together with list of U. S. intelligent appreciation of the sanity of our Carter Motor Co. 50 stockists rushed Air Afail to you. technical arguments; and faith that in sending Chicago Transformer Division 37 NOTE: We despatch by insured mail per their money out into the blue waters of the Cinema Engineering Co. 36 return upon receipt of your ordinary dollar Atlantic and beyond, they would get something check. good in return. Classified Ads 62 Jobbers are invited to handle the trans- Daven Co., The Cover 3 former that the States is eager to buy Eighteen months ago we gave the opinions - Dept. of National Defence 48 remember, immediate delivery from large of seven dissatisfied users of the 215. Since stocks in New York! Dorf, Richard H. 62 no the contrary, then we have had others. On PARTRIDGE TRANSFORMERS Garrard Sales Corp. 11 LTD. the pile of wonderful testimonials we get stead- ROEBUCK ROAD, TOLWORTH, SURREY. ENGLAND ily grows taller and, although we thought the General Radio Co. 27 215 a good Speaker before we dared to offer it Goodman Industries, Ltd. 48 to you, we prefer you to ask the man who Hartley, H. A. Co., Ltd. 64 let him down. -sue trusted us and found we did not Harvey Radio Co., Inc. 40 / Heath Co., The 53 A day or two ago, we had a letter: "How easy it is to become lost in the barrage of high - Hughes Research & Development Labs. 57 pressure advertising that audio enthusiasts here Hycor Co. 52 In your own LIVING ROOM I with are subjected to. have been bombarded Jensen Manufacturing Co. 31 full color literature about co -axial Speakers r_, with fancy Kellogg Switchboard & Supply Co. 54 as well as all sorts of single Speakers x cti_ u n iSlaas cones. Although the "axials" appear to be on Kierulff & Co. 38, 42, 50, 56, 59, 63 the increase I have not as yet heard rumors of Klipsch & Associates 62 be a quatra- axial, but that should the logical Lansing Sound Inc., James B. 56 outcome of the trend. Reading all this is dis- Leak Amplifiers 11 quieting and buying a Speaker is a real financial Leonard Radio Inc. 45 trauma." LeBel, C. J. 62 Our literature is not polychromatic, nor are Magnecord, Inc. 39 arguments highly -coloured. We our technical McIntosh Engineering Laboratory, Inc. 46 need not shout the odds, for the 215 speaks Neely Enterprises 5 in a cool, clear voice free from distortion. What we say, with cool, clear confidence is that, if Newcomb Audio Products Co. 51 you really know what music sounds like, the Partridge Transformers Ltd. 64 104" "s 215 at $48.00 will give you greater pleasure Permoflux Corp. 41 than any other speaker at any price. Ask the reproduction Presto Recording Corp. 7 man who owns one. Professional Directory 62

Send a dollar bill today for "New Notes in Radio Corporation of America .... 1, 8, 9 Radio" and a regular mailing of worthwhile Radio Shack Corp. 47 technical data. Present subscribers please note Rek -O -Kut Co. 4 a new oacket of info will soon be on the way. Standard Transformer Corp. 49 Stephens Manufacturing Co. 61, 63 Model 1OC3 * r Illustrated literature is free on request. Tartak - Stolle Electronics, Inc. 62 Tech Laboratories, Inc. 54 the BROOK High Quality All -Triode Thermador Electric Mfg. Co. 33 AUDIO AMPLIFIER Triad Transformer Mfg. Co. 38 H. A. HARTLEY CO. LTD. Write for free Technical Bulletin, detailed Distortion U. S. Recording Co. 62 Analysis A booklet "Better Listening" 152, Hammersmith Road United Transformer Co. Cover 4 Brook Electronics, Inc., Dept. AH -1 London W.6, England 34 DeHart Place, Elisabeth, New Jersey

64 AUDIO ENGINEERING AUGUST, 1951 DECADE RESISTANCE BOX TYPE 750 Prime Supplier of Electronic Instruments of Unparalleled Quality, Accuracy and Dependability

In the manufacturing of sensitive, accurate instruments, the reputation of the Daven organization is world wide. For substantially more than a generation, specialization in electronics, coupled with unexcelled development and engineering personnel, has thrust HIGH FREQUENCY ATTENUATION BOX TYPE 795 the Daven Company far in the forefront of producers instruments of notable quality.

Shown on this page is only a small part of the Daven line When writing for more complete CMCCIED information on the unit, illustrated. please identify h name l.. and moJcl number.

VOLUME LEVEL INDICATOR SERIES 910 -911

!I/7;r,- OUTPUT POWER METER TYPE OP -962

RF ATTENUATION BOX TYPE 650

DISTORTION 8 NOISE METER TYPE 35 -A

ATTENUATION BOX SERIES 690

FREQUENCY METER TYPE 838A

Precision equipment demands the finest components. Always specify Daven Allen uators.

GAIN SET TYPE 11A HIGH FIDELITY .... SMALL SIZE .... FROM STOCK

UTC Ultra compact audio units are small and light in weight, ideally suited to remote amplifier and similar compact equipment. High fidelity is obtainable in all individual units, the frequency response being ± 2 DB from 30 to 20,000 cycles. True hum balancing coil structure combined with a high conductivity die cast outer cas:, effects good inductive shielding.

Type Secondary List No. Application Primary Impedance Impedance Price A -10 Low impedance mike, pickup, 50, 125/150, 200/250, 50 ohms $16.00 or multiple line to grid 333, 500 /600 ohms A -11 Low impedance mike, pickup, 50, 200, 500 50,000 ohms 18.00 or line to 1 or 2 grids (multiple alloy shields for low hum pickup) A12 Low impedance mike, pickup, 50, 125/150, 200/250, 80,000 ohms overa I, or multiple line to grids 333, 500 /600 ohms in two sections 16.00 A -14 Dynamic microphone to one 30 ohms 50,000 ohms oyera I, or two grids in two sections 17.00 A -20 Mixing, mike, pickup, or mul- 50, 125/150, 200/250, 50, 125/150, 200/250, tiple line to line 333, 500/600 ohms 333, 500 /600 ohms 16.00 A -21 mixing, low impedance mike, 50, 200/250, 500 /600 50, 200/250, 500/600 18.00 pickup, or line to line (multiple alloy shields for low hum pickup) A16 Single plate to single grid 15.000 ohms 60.000 ohms, 2q ratio 15.00 A17 Single plate to single grid As above As above 17.00 8 MA unbalanced D.C. A -18 Single plate to two grids. 15,000 ohms 80,000 ohms overa I, Split primary 2.3:1 turn ratio 16.00 A -19 Single plate to two grids 8 15,000 ohms 80.000 ohms overall, MA unbalanced D.C. 2.3:1 turn ratio 19.00 A -24 Single plate to multiple line 15,000 ohms 50, 125/150. 200 ¡250 TYPE A CASE Mk Ma 10 1M OM Oa 16.00 333, 500/600 ohm; 11/2" 2" high A -25 Single plate to multiple line 15.000 ohms 50, 125/150, 200/250, A-20 8 MA unbalanced D.C. 333, 500/600 ohm; 17.00 A -26 Push pull low level plates to 30,000 ohms 50. 125/150. 2001250, multiple line plate to plate 333, 500/600 ohm; 16.00 A -27 Crystal microphone to mul- 100,000 ohms 50. 125/150. 200;250, fiole line 333. 500 /600 ohm; 16.00 A -30 Audiochoke.250 henrys 5 MA 6000 ohms D.C. .65 henrys M, 10 MA 1500 ohms D.0 12.00 A 32 Filter -24 choke 60 henrys 15 MA 2000 ohms D.C. .15 henrys ,,, 30 MA 500 ohms D.0 10.00

C4tr L MOMO MaMifaOaitaMr.e UTC OUNCER components represent the acme in compact quality transformers. These units, which weigh one ounce, are fully impregnated and sealed in a drawn aluminum housing 7/e" diameter ...mounting . . r. xó M.mM. opposite terminal board. High fidelity characteristics are provided, uniform from 40 to 15,000 cycles, «: except for 0-14, 0 -15, and units carrying DC which are intended for voice frequencies from 150 to 0 -2 4,000 cycles. Maximum level 0 DB.

ow awe t.., .. Type List .x:M . . No. Application Pri. Imp. Sec. Imp. Price 0-1 Mike, pickup or line to 50, 200/250 50,000 514.00 o-7I II 1 grid 500/600 0.2 Mike, pickup or line to 50,200/250 50,000 14.00 J 2 grids 500/600 4r----7 Í I Pa 0.3 Dynamic mike to 1 grid 7.5/30 50,000 13.00 0-4 Single plate to 1 grid 15,000 60,000 11.00

0-5 Plate to grid, O.C. in Pri. 15,000 60,000 L 1.00 0-6 Single plate to 2 grids 15,000 95,000 13.00 0-7 Plate to 2 grids, 15,000 95,000 13.00 D.C. in Pri. OUNCER 0-8 Single plate to line 15,000 50, 200 /250, 500/600 14.00 CASE 0 -9 Plate to line, D.C. in Pri. 15,000 50, 200/250, 500 /600 14.00 O-l3 7/e" Dia. x 11/e" high o -10 Push pull plates to line 30,000 ohms 50, 200/250, 500/600 1-1.00 plate to plate 0.11 Crystal mike to line 50,000 50, 200/250, 500 /600 14.00 i 0 -12 Mixing and matching 50, 200 /250 50, 200/250, 500/600 13.00 M . 0-13 Reactor, 300 Hys. -no D.C.; 50 Hys. -3 MA. D.C., 6000 ohms 10.00 WI. o c 0-14 50:1 mike or line to arid 200 1/2 megohm 14.00

0 -15 101 single plate to grid 15,000 1 megohm 14.00

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