Audio Engineering March, 1949 Enco Capacitors

MARCH 1949 Which ingredient is the secret

of * leadership?

NITROCELLULOSE

PLASTICIZERS

RESINS

OIL

DYE

fy, SOLVENTS

7, MOISTURE RESISTING AGENT

THE FIRST SIX of these ingredients are to be found in any lacquer for professional discs. The seventh is an exclusive AUDIODISC development that provides permanent resistance to humidity. This, however, is a fairly recent improvement, and therefore does not account for the consistent uniform quality that has made AuDIODISCS the first choice of discriminating recordists for the past 10 years. The "secret" lies not in any one ingredient, but in the correct selection, exact proportioning, and precise chemical control of all of them. In the ultra filtration, quality control, uncompromising inspection, and patented precision coating process. All of these factors, backed by continual research and exhaustive production testing, assure matchless recording quality in every AUDIODISC.

eReg. U.S. Pat. Off.

Audiodisu are manu/actured in the U.S.A. under exclusive license porn PYRAL, S. A.R. L.. Paris

Audio Devices, Inc., 444 Madison Ave., N.Y. C.

EXPORT DEPT.: ROCKE INTERNATIONAL, 13 EAST 40TH Sr., NEW YORK 16, N.Y.

ae,-0e-alA aemse4" v

The farmer in the field and his wife at home will be able to converse with ease by using pipt these new, lightweight transceivers equipped with Sylvania -_j sub -miniature tubes!

Tiny Sylvania sub -miniature radio ers, hunters, industrial users, tubes, smaller than a lady's little rangers and those who wish boat - finger, are big reasons why the to -home and auto -to -home com- Citizens Radio Transceiver meas- munications. ures only 6" long, not quite 3" wide, Sylvania's extensive radio tube 11/y" deep, and weighs only eleven research and manufacturing skill ounces! have made Sylvania sub -miniature

Ci ill !NS TRA"StnivtF Sold in sets of two, these tiny tubes the choice of Citizens Radio two-way transceivers with a range Corporation, Cleveland, for this of several miles are tuned to 465 revolutionary, civilian transceiver. mc. Among the many who want Sylvania Electric Products Inc., these handy units are police and Radio Tube Division, Emporium, fire departments, surveyors, farm- Pennsylvania. SYLI' NIA I1LEC

RADIO TUBES; CATHODE RAY TUBES; ELECTRONIC DEVICES; FLUORESCENT

LAMPS, FIXTURES, WIRING DEVICES; LIGHT BULBS; PHOTOLAMPS AUDIO ENGINEERING MARCH, 1949 ENCO CAPACITORS

Leaders because they perform reliably under all operating conditions, these fixed mica dielectric capacitors are used in electronic applications wherever long life and successful performance are demanded.

Each tiny El -Menco Capacitor must pass life and humidity tests; meet standards set by the United States Army and Navy; pass tests at double their working voltages; prove their dielectric strength, temperature co- efficient and capacitance drift, and have their insulation resistance double- checked. These little leaders i-i are molded in low -loss bakelite and wax -dipped for salt water immersion seal. They're available in a wide range, all impregnated, all precision -made, all JAN, RMA and RCM color- coded.

CM 15 MINIATURE CAPACITOR Why not protect your product's Actual Size h" x %" x 3 " performance with capacitors made For Radio, Television and Other Electronic Applications under these rigid conditions? 2 to 420 mmf. capacity at 500v DCA 2 to 525 mmf. capacity at 300v DCA Temp. Co- efficient ± 50 parts per Specify EL -MENCO million per degree C for most TESTED RELIABLE LEADERS! capacity values 6 -dot standard color coded THE ELECTRO MOTIVE MFG. CO., Inc. WILLIMANTIC CONNECTICUT

Write on your firm letterhead for Catalog and Samples MOLDED MICA El-lYlenc 0 MICA TRIMMER CAPACITORS FOREIGN RADIO AND ELECTRONIC MANUFACTURERS COMMUNICATE DIRECT WITH OUR EXPORT DEPT. AT WILLIMANTIC, CONN. ARCO ELECTRONICS, INC. 135 Liberty St., New York, N. Y. -Sole Agent for Jobbers and Distributors in U.S. and Canada

2 AUDIO ENGINEERING MARCH, 1949 John H. Potts, Editor and Publisher

C. G. McProud, Managing Editor S. L. Cahn. Adv. Director Lawrence LeKashman, Asst. Editor H. N. Reises. Adv. Mgr. AU Cs Louisa B. Dresser, Edit. Prod. Mgr. L. J. Devine, Circ. Mgr. Editorial Advisory Board Representatives ENGINEERING Howard A. Chinn Sanford R. Cowan. Mid-West Sales 342 Madison Ave., New York 17, N. Y. John D. Colvin C. J. LeBel James C. Galloway 816 W. 5th St., Los Angeles 13, Calif. J. P. Maxfield rltrRRR Dale International Publications, Lfd. George M. Nixon 105 Sf., London W. 1, England UDIT Successor to Bolsover UREAU RADIA Winston Wells Harris & Floyd. 297 Swanston Sf. KULATp I, S. Young White Melbourne C. Victoria, Australia

Established 1917 CONTENTS MARCH, 1949 Vol. 33, No. 3

Editor's Report

Characteristics of the New 15 RPM Record-"Stylus" 6

Audio Technique in Television Broadcasting -R. H. Tanner 9

A Versatile Phonograph Preamplifier-Paul Si. George and Benjamin B. Drisko l 1

Compact 6AS7G Amplifier for Home Reproduction Systems. Part I-C. G. McProud 17

Experimental Ultrasonics, Part I -S. Young While 20

Problems in Audio Engineering -Lewis S. Good/riend 23

WMGM Master Control Equipment Design -M. E. Gunn 21

Record Revue -Edward Tarnall Canby 30

New Products 32

Advertising Index .18

COVER

Array of springs driven by magnetostriction pulse generator feeding a 10 microsecond pulse into 5 individual pickups. Oscillograph screen pattern shows echoes as they occur when the output of the pickups is fed into the amplifier. This extraordinary photo was made by Winston Wells.

AUDIO ENGINEERING (title registered C. S. Pat. Off.) is published monthly at New York, N. Y., by Radio Magazines, Inc., J. H. Potts. President; Lawrence LeKashman, Vice Pres. Executive and Editorial Offices at 342 Madison Avenue, Nev) York 17. N. Y. Subscription rates - United States. U. S. Possessions and Canada. $3.00 for I year. 35.00 for 2 years: elsewhere E4.00 per year. Single copies 35e. Printed in U. S. A. All rights ed. Entire contents copyright 1949 by Radio Magazines. Inc. Entered as Second Class Matter July 29, 1948 at the Post Office. New York, N. Y.. under the Act of March 3. 1879.

AUDIO ENGINEERING MARCH, 1949 3 EDITOR'S REPORT

ONE PICKUP FOR AU. RECORDINGS on his own hook and entirely without solicitation. We hope the new appearance pleases our readers as much ON THE HEELS of the discussion about various as it did us. speeds for phonograph records comes the thought that two different pickups, or their equivalent, are required to reproduce the now existing types of record- MORE AUDIO FALLACIES ings. Comparing the grooves used in the present three In talking with W. S. Barrel!, technical director of systems, it is obvious that the angle between the side walls EMI, who is presently visiting this country, the matter remains the same, and the only apparent difference is in of wide frequency range in recording was brought up. the tip radius of the cutting stylus. While a standard Many have wondered, he tells us, why he records up to 3 -mil reproducing stylus cannot be used on the fine 20,000 cycles in his HMV studios, far higher than grooves, there is no reason why the 1 -mil microgroove normal hearing range. According to their tests, the ear stylus should not be able to follow the standard groove notes a difference in a complex tone if the reproducing successfully if the tip radius of the recording stylus, about system is limited to a lower frequency, even if the listen- .25 mil, is maintained at approximately the same value er cannot hear a pure tone of much lower pitch. Just for both types of recording. This idea is expounded why this is so will he discussed in an article now in more completely by "Stylus" in the article commencing preparation. on page 6. We believe a more thorough understanding of the Some experimental work has been done with the nature of hearing and the manner in which the ear func- sharper stylus on standard -pitch acetate recordings, with tions will do much to clarify our thinking in designing an appreciable improvement in frequency response and sound -reproducing apparatus. The familiar argument, to the over -all performance. Needless say, a change in "What's the use of going to the trouble and expense of would recording stylus dimensions not immediately alle- making really fine, high -fidelity apparatus when no one viate the problem of the user, but as existing recordings can hear over such a wide range ?" needs a lot of clarifi- are withdrawn and worn -out records replaced by those cation. This, we are convinced, can only be done by start- cut with the suggested stylus, it would some day be pos- ing all over again along the lines which Maxfield has sible to play all records with a single pickup and stylus. preached, basing our thought on the results of subjective It would, of coure, be necessary to change the needle tests. There seems to be more faulty reasoning about pressure for the finer groove, but this is simple to do. audio engineering than in other branches of electronic engineering. In other words, many "sound" ideas are OUR NEW COVER fundamentally unsound. The new design on our cover and masthead is the work Our book division is now preparing for publication of Mr. Fred Walworth, Audio Facilities Engineer of the three books in the sound field. One will cover in detail American Broadcasting Company in New York. Mr. from an engineering standpoint, disc, wire, and tape re- Walworth, a serious student of industrial design in his cording. The other two will deal with audio equipment spare time, pointed out that our old design was not in design and operation of audio equipment. A more de- keeping with modern principles, and offered the new one - tailed announcement will appear in our next issue.

4 AUDIO ENGINEERING MARCH, 1949 TWO new Hypex* Projectors - designed for 360 - MODEL VR -11 "THREE- SIXTY" HYPEX degree sound dispersal -are now available. With (above) 15 WATTS 280 CPS CUTOFF sound distributed horizontally in these new MODEL VR -241 "THREE- SIXTY" HYPEX all directions, (at right) 25 WATTS, 140 CPS CUT OFF. models are intended for installations where coverage of relatively large areas and suspension from the ceiling are desired. Like all Hypex Projectors, these radial units incorporate the famous Hypex formulat which results in improved acoustic performance. Jensen By the addition of the two radials to the four previously announced Hypex units illustrated below, the Hypex line now includes a model for every "sound" need, indoors or out- doors.

*Trade Mark Registered +Patent 2,37S,262 JENSEN MANUFACTURING COMPANY Write for Data Sheet 143

6633 SOUTH LARAMIE AVENUE, CHICAGO 38, ILLINOIS In Canada: COPPER WIRE PRODUCTS, LTD., 351 CARLAW AVENUE, 'TORONTO ti

MODEL VH-24 HYPEX MODEL VH -20 HYPEX MODEL VH -15 HYPEX MODEL VH -91 HYPEX 25 WATTS; 110 CPS CUT -OFF 25 WATTS; 140 CPS CUT -OFF 15 WATTS, 180 CPS CUTOFF 15 WATTS, 300 CPS CUT-OFF

AUDIO ENGINEERING MARCH, 1949 5 Characteristics Of The New 45 RPM Record ,,e4 OF THESE MICROPHONES By "Stylus" HAS THE SUPER -CARDIOID TIIERE has been widespread interest in the new 45 rpm RCA Vic- PICKUP PATTERN THAT tor record, often called "Ma- dame X" or "X." A complete lack of official REDUCES FEEDBACK BY technical information has hin- 73z,' dered public acceptance. Much of the unofficial information floating around in non -recording circles has been wildly inaccurate. Record manufacturers, radio -set designers, and record - changer manufacturers have received a certain amount of accurate information, which we have pooled to prepare THE FAMOUS «55" this discussion. What it is "X" is an attempt to develop a LIST PRICE UNIDYNE DYNAMIC more compact, lower -cost record of higher quality than the ordinary shel- $67" Unidirectional Microphone. This superlative lac type. It is aimed chiefly at the dynamic microphone is a Multi- Impedance popular market-which includes Microphone -you can have either High, Me- 80% 1 of all disc dium, or Low Impedance simply by turning sales. The record a switch! Because it is a Super-Cardioid, the is rather thin, 7 inches in "Unidyne" kills Feedback energy by 73 %- diameter, and made of unfilled making it possible to use under the most vinylite. The center hole is l'A inches difficult acoustic conditions. The "Unidyne" in diameter, and the label is surround- is probably the most widely used microphone ed by a raised plateau which keeps throughout the world: Recommended for all the recorded surfaces out of contact Multi- Impedance Switch highest quality general -purpose uses. and free from scratches The maxi- For Low, Medium or High mum playing time is about 5 minutes, Impedance. but 3- minute records are made with the same diameter. The stop groove is concentric with the center. The price will be about ten cents less than that of a conventional shellac of the same playing time. The groove has an included angle of 83 degrees and n radius of about .25 mil; it can be played by the same recording stylus as used for LP, one with a tip radius of .9 to 1 mil. How it is Used The large center hole is designed THE NEW "737A" to permit the use of a new record changer design. The record stack is MONOPLEX CRYSTAL carried on n 1% -inch diameter center spindle, and there are no knife Unidirectional Microphone. The "Monoplex" is the ONLY blades to support the outer edges. Super -Cardioid Crystal Microphone made. As such, it is The center spindle contains most of undoubtedly the finest of all crystal microphones. (A the changing mechanism. The entire comparative test will LIST PRICE prove this statement convincingly.) changer is therefore ultracompact- The "Monoplez" employs the same type of acoustic $3975 it will fit in the palm of your hand. phase -shifting network used in the highest cost Shure The concentric stop groove permits Broadcast Microphones. Has "Metal Seal" crystal -will the use of a lower -cost, foster -trip withstand adverse climatic conditions. Can be used in mechanism. As n result, the those applications where severe background noise would changing cycle is very rapid: The make conventional microphones practically useless! cycle itself takes about 1% seconds. The entire changing time is longer than this by the time to play the lead -out and lead -in grooves, so that observers Lfeenea under, patenta of Brush Droelopment Company. S. peunte pendlnp. have checked the total at three to SHURE BROTHERS, four seconds. The simplicity of the Inc. mechanism leads to much lower cost Microphones and Acoustic Devices -a list price of about twenty -five dollars. 225 West Huron Street, Chicago 10, Illinois Cable Address: SHUR4MICRO iContinued on page 461

6 AUDIO ENGINEERING MARCH, 1949 330B DISTORTION AN: ER

CHECK THESE SEVEN IMPORTANT FUNCTIONS:

1. Measures total audio distortion. 2. Checks distortion of modulated r -f carrier. 3. Determines voltage level, power output. 4. Measures amplifier gain and response. 5. Directly measures audio noise and hum. 6. Determines unknown audio frequencies. Any frequency between 20 and 20.000 c.ps. 7. Serves as high -gain, wide - band stabilized amplifier.

20 200 2000 FREQUENCY, c.p.s. Figure 1

This fast, versatile -hp- 330B Analyzer ranges are provided: .03, .1, .3, 1.0, Measures Direct From R -F Carrier measures distortion at any frequency 3.0, 10, 30, 100 and 300. Calibration The -bp- 330B incorporates a linear from 20 cps to 20 kc. Measurements from +2 to -12 db is provided, and r -f detector to rectify the transmitted are made by eliminating the funda- ranges are related in 10 db steps. carrier, and input circuits are contin- mental and comparing the ratio of the The amplifier of the instrument can uously variable from 500 kc to 60 me original wave with the total of re- be used in cascade with the vacuum in 6 bands. maining harmonic components. This tube voltmeter to increase its sensitiv- Ease of operation, universal appli- comparison is made with a built -in ity 100 times for noise and hum cability, great stability and light vacuum tube voltmeter. measurements. weight of this unique -bp- 330B Ana- The unique -bp- resistance -tuned Accuracy throughout is approxi- lyzer make it ideal for almost any circuit used in this instrument is mately ±3% and is unaffected by audio measurement in laboratory, adapted from the famous -bp- 200 changing of tubes or line voltage var- broadcast or production line work. series oscillators. It provides almost iations. Output of the voltmeter has Full details are immediately avail- infinite attenuation at one chosen fre- terminals for connection to an oscil- able. Write or wire for them -today quency. All other frequencies are loscope, to permit visual presentation Hewlett -Packard Company, 1437L passed at the normal 20 db gain of of wave under measurement. Page Mill Road, Palo Alto, Calif. the amplifier. Figure 1 shows how at- " tenuation of approximately 80 db is "RV' .1111Pg achieved at any pre -selected point between 20 cps and 20 kc. Rejection is so sharp that second and higher har- monics are attenuated less than 10 %. laboratory instrument Full- Fledged Voltmeter As a high - impedance, wide- range, high- sensitivity vacuum tube voltme- Noise and Distortion Analyzers Ware Analyzers Frequency Meters ter, this -bp- 330B gives precision Audio Frequency Oscillators Audio Signal Generators Vacuum Tube Voltmeters response fiat at any frequency from Amplifiers Power Supplies UHF Signal Generators Attenuators 10 cps to 100 kc. Nine full -scale Square Ware Generators Frequency Standards Electronic Tachometers

AUDIO ENGINEERING MARCH. 1949 7 PERMANENT MAGNETS

As electrical constituents go, permanent magnets are reja. tively new. They made tremendous advances within the past decade, especially in the communications and aviation industries, and in the general fields of instruments, controls, meters and mechanical holding devices. Many of these uses were problems that just couldn't be solved until permanent magnet materials were developed to do the job-a work of pioneering to which Arnold con- tributed a heavy share. Many other applications were those where permanent magnets supplanted older materials because of their inherent ability to save weight, size and production time, as well as greatly improve the performance of the equipment. To these advantages, Arnold Permanent Magnets add another very important value -standards of quality and uniformity that are unmatched within the industry. Arnold Products are 100% quality -controlled at every step of manufacture. What's more, they're available in all Alnico grades and other types of magnetic materials, in cast or sintered forms, and in any shape, size or degree of finish you need. Let's get our engineers together on your magnet applications or problems.

THE ARNOLD ENGINEERING CO.

ALLEGHENY LUDLUM STEEL CORPORATION 147 East Ontario Street, Chicago 11, Illinois

Specialists and Leader: in the Des ign,Enyineering and Manufacture of PERMANENT MAGNETS

8 AUDIO ENGINEERING MARCH, 1949 View in WCBS -TV studio of the CBS network in New York. AUDIO TECHNIQUE 9n jrìkvbsioii &ìwadcaiithzq R. H. TANNER*

How TV audio technique differs from other sound pickup methods.

IN VIEW of all the exciting newness ther from the truth and this article compete for position with cameras, of results, circuitry and general is intended to survey this compar- lamps and so on. Except on rare oc- technique, it is only natural that atively new audio field and to point casions, it must not appear in the the video side of television has been out its difficulties, challenges and picture nor must its shadow be cast the subject of innumerable articles possibilities. on the scene. But sound filin en- during the past few years, while the gineers have several great advan- problems of producing the very nec- Differences in Technique tages over their television counter- essary sound program which accom- parts. Firstly, it is the established panies and clarifies the picture has First then, it must be pointed out practice in motion picture studios to received little publicity. In fact, it briefly how the technique of TV record the action in short sequences is probable that few people, whether audio differs from the older and more lasting from a few seconds for a few engineers or not, unless they are in- established arts of sound broadcast- minutes, and ample time is allowed timately connected with television. ing and motion picture recording. In for determining the best position realize that TV audio presents prob- the broadcast studio, the microphone for a fixed microphone, or for re- lems often very different from those is all important and the entire ener- hearsing the movements if a travel- encountered in either straight sound gies of engineers, artists and pro- ling shot is required. In the same broadcasting or in motion picture ducer are concentrated in obtaining way, time is available for the inevit- recording. Experience gained in the a final sound output which inter- able arguments between sound staff world's first public television service prets, as fully as possible, the pro- and lighting engineers on the sub- (in England prior to World War II) ducer's ideas. Any number of mi- ject of microphone shadows, with indicates that even in the studios crophones may be used, in one or more hope of arriving at a satisfac- actors, musicians themselves there are often many, more studios, and tory compromise solution. It is in- sound may he principally concerned with the visual and other sources of teresting to note that an average of with no re- side of the business, who are apt to arranged and grouped three minutes of finished film per gard whatever to the visual effect, write off the activities of the sound day of shooting is considered good but solely with a view to producing staff as a necessary evil, the applica- going, whereas the staff of a tele- the desired aural result. tion of a known art, without tbe ex- vision studio will probably have to perimental and pioneering interest In motion picture recording, the produce at least one and a half hours which is so obviously a part of video situation is very different. As in of finished program a day, and their work. In actual fact, nothing is fur- television, the visual arrangement of efforts will certainly have to stand actors, scenery, etc., becomes para- comparison with the movies at the *Audio Equipment Engineer, Northern Electric Co., Ltd., Belleville, Ont., Canada. mount, and the microphone has to viewer's local theatre.

AUDIO ENGINEERING MARCH, 1949 9 ly when a program was accompanied by an orchestra "off- stage ", the orchestra was placed at the Control Room end, while action took place at the other. This suggests that the Control Room end should be made live and the other end more or less dead, to'provide good acoustic conditions for the music. On the other hand, on occasions when the orchestra itself is televised, it will occupy the other end of the studio and exactly the reverse will hold good. In addition, it would be a disadvantage during the performance of plays to have the control room end live, since this is then the region where most of the unwanted studio noise originates, and reverberation will tend to reinforce it. Fig. I. Measured reverberation time vs. frequency curve of Studio A, London It will be seen, therfore, that a TV Station. television studio should be able to provide ni a n y different acoustic Secondly, the techniques of pre - produced under the same acoustic characteristics. Scenery is, in gener- and post- recording have reached a conditions, except insofar as the al, of little assistance as is very high standard of perfection, properties of the studio may he af- it delib- erately trade and enable good results t o be fected by scenery, screens or variable as light and non -rigid as possible in order to achieved which would be quite im- wall treatment. Since it is certain facilitate handling. will possible if the sound were recorded that at some time or another the It not therefore con- very much to at the same time as the scene is pho- characteristics of a small living room tribute the room acoustics tographed. In general, therefore, the must be simulated, it must be pos- except at the higher frequencies where it motion picture engineer has much sible to make the studio practically will add to the dispersion and absorption. would more time at his disposal both dur- dead, which in the absence of very It seem that some form of variable acoustic treating the shooting of the film and its elaborate means for varying t h e ment is required, so subsequent editing. acoustics, sets a limit to the maxi- that not only can reverberation On the other hand, the difficulties mum reverberation achievable, with- the time of the studio as a whole be altered, which beset the TV audio engineer out recourse to such devices as echo but different areas can be made live or are many and varied. As in the rooms. The measured reverberation vs. dead as required. Experience with movie studio, he is competing for frequency curve for Studio A is re- acoustic screens in ordinary sound space with many others, except that produced in Fig. 1, from which it studios suggests television the available space is usually even will be seen that the maximum rev- that scenery might, with advantage, be so de- more restricted. Owing to the con- erberation time of about 1 second signed as to provide a suitable acous- tinuous nature of a television per- occurs at low frequencies, the curve tic, as well as scenic, effect. Such formance, he has no "dead" time at showing a gradual decrease in rever- scenery, however, would all in which to make adjustments beration as the frequency i s in- demand considerable skill in handling to once the program has started. For creased until at 8000 c/s the period give the effect desired. the same reason, lighting comprom- has dropped to 0.5 second. ises must be achieved during the all One method of dealing with this fundamental too short rehearsal period before Another difficulty problem which is attractive at first may be explained by transmission. Obviously the micro- reference to sight, is to make the studio as dead Fig. 2, which shows a plan phone must be more mobile than in view of as possible and add all the reverber- the same studio. In general, especial- a motion picture studio, and the ap- ation required by means of an echo pearance "in shot" of either itself -- SLIDING DOORS - or its shadow must be avoided by a , _l PASSAGE continuous display of skill on the part of the operator. This is but one of the many problems presented to the TV sound engineers; many oth- 29' ers will emerge later in this article.

Acoustics of Television Studios ORCHESTRA ACTION For both economic and technical END END reasons, television studios cannot be provided in such numbers. nor with such a variety of sizes and characteristics, as broadcasting studios. Thus, the London Television Station has _77 n__ -- r only two, both of which are virtually SCENE DOCK identical in size a n d equipment. This means that all programs are Fig. 2. Plan view, Studio A, London Television Station.

IO AUDIO ENGINEERING MARCH, 1949 room. This method is in use to some extent in the United States but has several disadvantages. Firstly, a dead studio is most depressing to actors, musicians and staff, and would almost certainly tend to reduce the standard of performance. Secondly, it is often not fully realized that the use of an echo room of long period cannot give the same result as a studio of shorter reverberation time, no matter what proportion of echo is mixed with the direct sound. This is illustrated in Fig. 3. In curve (a), left, idealized decay of sound in normal studio is shown. Fig. 3. Curve (a) shows an idealized Curve (b), right, shows decay when echo room is used with dead studio. decay of sound in a normal studio. The steady sound at a level OA is ways faced with the problem of en- cut off at point B. The sound reach- recording stages used ..in the film his matches the ing the microphone direct disappears world. This would have characteris- suring that sound picture. normal broadcasting, a as indicated by the drop BC and the tics suitable for the size of orchestra In two people may reverherent sound dies away along normally used f o r accompanying whole scene between the actors and the the line CD. Changes in reverbera- television programs, and the conduc- be played with relative pos- tion time will alter the slope of the tor would be provided with head- microphone in the same television, unless the scene line CD as shown by CD'. In the phones and a viewing screen to keep itions. In very will be necessary to case of the dead studio and echo him in touch with the vision studio. is short, it view point at fairly fre- room the decay is as shown in Curve This technique was occasionally used change the intervals by switching from (b). When the sound is cut off, the in Britain before the war, when one quent to another. Ideally, drop in level, FG is far greater than of the two studios was used for o n e camera whenever this occurs, the sound the corresponding drop BC if the vision and the other for the orch- as well. In practice total time of decay to some arbitrary estra. should change will usually happen only when zero level is to be kept the same. Microphones and Microphone this the change of view point is consid- This must be so since the rate of de- Technique erable, as for example, when going cay in the echo room, as given by in micro- 'l'he main differences from close -up to long shot. In this the slope of the line GH, is much with phone technique, as compared ease, the change in sound is more or smaller than the corresponding rate which broadcasting and film work, less automatic owing to the necessity in the live studio (given by the slope the requirements of television de- for withdrawing the microphone out of CD). The slope of GH is fixed by in mand, have already been outlined of before the cameras a r e the design of the echo room and the shot the introduction. In general, it is changed. only control available is the propor- difficult to work with the microphone tion of echo to direct sound. An in- as close to the performers as is de- A rather less obvious example is crease in this proportion will give sirable while keeping both the mi- illustrated in Fig. 4, in which the some such decay curve as EFJT(. crophone and its shadow out of the two characters A and B are engaged What would really be required, picture. In this respect, matters are in conversation. Two cameras 1 and then, is a whole series of echo rooms, made worse by the fact that lighting 2 are in use alternately to give a or sources of synthetic reverbera- arrangements are set for the dura- varying viewpoint. It might h e tion. possessing a range of acoustic tion of the scene and cannot, as a thought that, at such close quarters, properties. The one which simulates normal rule, be altered for individual the position of the microphone is un- most closely the conditions under shots in order to avoid shadows. important, and that some such posi- which the action is supposed to be Apart from these mechanical dif- tion as indicated by Mic. 3 would taking place would then be selected ficulties, the sound engineer is al- suffice, no matter which camera was and made available to the sound control engineer, who would alter the amount of added reverberation to correspond to the length of visual shot. Thus, for close -ups, little or no added echo would be needed, while for long shots the amount would be increased. The provision of, say, five echo rooms would occupy considerable space. However, if a satisfactory electrical or electro- mechanical system could be devised to perform the same function, a valuable saving might be possible. One further question which must be considered under the subject of acoustics is the desirability of providing a studio purely for sound purposes, comparable with the sound Fig. 4. Pictorial representation of microphone placement.

AUDIO ENGINEERING MARCH, 1949 through the air without giving rise to rumbles. This would appear to put velocity microphones at a disadvantage, although they are used, in various forms, in U.S. television studios. A distinction may, however, be made between the type of microphone used on the boom, which will in general have to deal only with speech, solo singing, or possibly emphasis of soloists in dance band programs, and the type of microphone which is slung in a fixed position for orchestral programs, etc. This distinction was, in fact, made in England before the war, when pressure microphones were used on the boom, and velocity microphones slung for the stationary pick -up purposes. In addition, it Fig. 5. Microphone placement for best signal -to -noise ratio. (See text.) would normally be permissible to insert a certain amount of low -fre- in use. This, however, ignores the chronized automatically. Figure 5, quency attenuation in circuits with polar diagram of the human head, however, shows this to be a fallacy. moving microphones without any ap- which at the higher frequencies be- The microphone position 1 is very preciable deterioration in quality, come quite sharp. When Camera 1 suitable for close ups (Artist A) but since the sources mentioned above is being used, B is facing the camera in the case of the long shot (Artist for which a moving microphone is while A has his back to it. Thus B's B) a much better position from the used are not rich in the lower fre- speech should be crisp and clear, point of view of signal -to -noise ratio quencies. Even the microphone used while A's should be slightly but dis- can be found, as shown by position to emphasize soloists will normally tinctly muffled. Changing to Camera 2, or if as would normally happen be mixed with a stationary one 2 reverses the position. Unimportant the giv- camera "pans down" somewhat, ing a general balance of the band or as this difference may seem, for op- position 3 would be better still. orchestra, and the emphasis or defin- timum results the operator should With the microphones in use in ition is conveyed mainly, if not en- swing the microphone between posi- Britain before the war, the main- tirely, by the higher frequencies, so tions 1 and 2 in step with the cam- tenance of a great enough signal -to- that attenuation of the bass is again era mixes. studio-noise ratio was always a prob- permissible. Many other examples of the need lem. The essential presence in the for acoustic perspective might be studio of cameramen and their as- Concealed Mikes quoted, in which the right effect sistants, sound operators, electri- On various occasions, when visual helps the picture to tell its story, cians, make -up staff, scene shifters, difficulties make it impossible to ad- while the wrong one destroys the il- etc., cannot fail to raise the level of here to the normal technique, it be- lusion. In televising dance bands, or background noise far above the value comes necessary to resort to con- musical scenes in general, an effort which would be thought normal for cealed microphones. Our experience should be made to emphasize slightly a broadcast studio. It would seem is that these are seldom successful, the sounds made by the instrumen- that the best solution to this prob- since they are inevitably placed in talists or singers actually appearing lem is a unidirectional microphone. close proximity to a variety of ob- in the picture. Many movies appear because in general, the unwanted jects, all of which play havoc with to ignore this principle and present noise comes from the side of the the resulting acoustic effect. There- complicated angle shots of various microphone remote from the players. fore, such concealment should sections of a band, the effect of In addition, unidirectional micro- only be employed under the most which is greatly marred by the fact phones would tend to reduce cross extreme pressure of circumstances, that the sound viewpoint remains pick -up, that is, for example, pick -up or perhaps to cover a very short in- fixed. In general, it may be said that of the orchestra on the soloist's mi- terval needed to awing the boom the attention paid to sound perspec- crophone and vice versa. It would from one set to another. Even in tive in motion pictures varies very probably help also in the problem of this last instance, it is unconvincing greatly from one to another, so that maintaining the balance in n musi- to open a scene with one tone quality in this field, as in others, television cal comedy between a singer moving and then, a second or two later, to might well lead the way. In this con- about the set, at varying distances replace it with another. nection it is interesting to compare from the camera, and a stationary It would seem that the technique what has been said above with a des- orchestra, since it could be worked of pre -recording, which has already cription of the problems encountered at a greater distance from the singer been mentioned briefly, would be of in foreign language synchronization while still providing the necessary great help to the television sound of films. (See References at end of voice -to- accompaniment ratio. Small engineer. The requisites are a good article.) variations in this distance will then sound studio, and an excellent re- Figure 4 suggests that a micro- have less effect. cording system. In the motion pic- phone might be mounted on each Another essential requirement for ture world, pre -recording is used for camera so that it is just out of the the microphone which is to be used nearly all complicated musical line of shot, and that camera and on the "boom" is that it should be scenes, in which the action may be microphone mixing might be syn- possible to move it fairly rapidly photographed many tunes from a

12 AUDIO ENGINEERING MARCH, 1949 wide variety of distances and angles. play, to insist that all accompanying Balance and Control The sound is recorded first, usually music and effects should be trans- While it is very difficult indeed to on vertically cut discs, and replayed mitted "live." However, since the fix the point at. which microphone onto a loudspeaker during "shunt- modern direct recording is capable technique ends and balance and con- ing," so that the cast may synchron- of giving considerably better results, trol begin, we may for the purpose ize their movements to the sound. both from the aspect of bandwidth of this paper make a division as Then when all the required shots and noise level, than the commercial suggested by the duties of the two have been taken, the director can depressing, it might be well worth ar- engineers concerned, t h e "studio cide on the method in which they ranging a system whereby perhaps sound" engineer and the "sound shall be "cut" and pieced together to once a week, a resident Television mixer." The former is concerned form the final sequence. Lastly, the Orchestra or other suitable combin- mainly with the positioning of mi- sound will be recorded onto film in ation recorded as much of t h e crophones relative to the performers such a way that it matches the pic- incidental music for forthcoming while the latter mixes the outputs of ture. It is at this stage that the shows as came within their scope. various microphones in the correct careful sound engineer will intro- In the saine way a library of sound proportions, and at the same time . duce artificial reverberation into the effects could be built up, new record- controls the output level to within s o u n d accompanying the longer ings being made as producers re- the dynamic range set by the lim- shots, and so adjust his volume levels quired them. itations of broadcast transmission as to suggest a sound perspective in Another sound source which must and reception. Once again, the bal- agreement with the picture. be catered to is the sound track of ancing of the various microphone In television, the technique could motion pictures. Again this will com- outputs will be more difficult than be very similar, except that, o f pare unfavorably with live sound di- in sound broadcasting, since, as has course, the marriage of sound and rect from the studio, but in general, been pointed out in the previous sec- picture would have to take place at movies will form separate items in tion, the microphones will seldom be the moment of transmission, and the program, and therefore it is prob- in the optimum positions for sound that the continuous nature of the able that the lower standard of qual- pick -up, so that correction for this television programme would again ity can more readily be tolerated. must be attempted at the mixing make heavy demands upon the skill However, it is likely that to an desk. The use of the moving micro- of the sound staff. Great importance increasing extent specially photo- phone does not make matters any would have to be attached to the graphed film excerpts will be in- easier, since it will be very difficult performance of the recording system cluded in television plays. Open air for the operator to keep it at a fixed used, since it should be impossible to and other scenes difficult to repro- distance from the performer. The detekt in the listener's home whether duce in the studio may well be shot maintenance of a satisfactory bal- or not a recording is being used. In in advance and included in the pro- ance between a moving singer picked view of the wide audio -frequency gram at the appropriate moment, as up on a moving microphone and a range transmitted, it is doubtful if was done on several occasions even stationary orchestra picked up on a any existing system would be really before the war. In these cases, the stationary microphone is a task satisfactory b u t developments in greatest care must again be taken which often presents itself during sound recording systems should soon with the sound recording to avoid floor show programs or in musical enable this condition to be met. In making the change from studio to comedies. When it is realized that, addition, very great care would have filin too obvious. In fact, it may well in addition, the sound mixer must to be taken, to ensure that the be preferable to reverse the technique contrive to modify t h i s balance quality and acoustic characteristics of pre -recording, by having the ac- somewhat to keep in line with the of the recorded sound agreed closely tors speaking the lines in the studio, varying lengths of picture shot, it with the live sound immediately pre- under suitable acoustic conditions, will be appreciated that a high order ceding and following the record, un- synchronizing their words to the of skill is called for, and that sound less, of course, there was a change mouth movements of the filin. In mixer and boom operator must work of scene. The arrangement for play- this way, although the visual half in very close harmony. As has been ing the record back into the studio, of the program is recorded, the sound suggested earlier, further complica- to secure synchronization, in such a will be transmitted "live." [Continued on page 41] way as to avoid the possibility of howl -back when the studio microphone is faded up, is already well 61IR55 established and was in fact in use 1 oRUMSó in England before the war. Ir ó05'00O Other Sound Sources Fig. 6. ,,,, O Quite apart from the possible use Typical 0 0000 of pre- recording, the standard disc, arrange- 022 MELDS whether a commercial pressing or ment for televising direct recording, is so valuable a source of incidental music or sound a dance that its use must be tolerated in band. spite of the ease with which, at pre- CAMERA 3 sent, such use may be detected by ,SLUNG OR ON BOOM) the listener. It would obviously add CAMERA E

vastly to the already considerable CAMERA expense of, for example, a television

AUDIO ENGINEERING MARCH, 1949 13 Versatile Phonograph PreampliFier

PAUL W. ST. GEORGE* and BENJAMIN B. DRISKO*

Design data for an excellent preamplifier.

AT THE COST of adding one more however; hut after protracted effort, corrective networks which does a far article to the mounting list of including tapping all known sources better job than the first fixed -curve those intended to solve the phono- of information, the following table system. With at least semi -certain graph preamplifier - equalizer prob- was built up. It is not necessarily ac- information to design from, a unit lem, the writer offers a more detailed curate but represents the best known can be built to fit the needs of the analysis and a more versatile solu- estimate of current recording curves: day. tion than has yet come to his attention. Low Freq. Hi Freq. Preemp. Freq. at which Turnover db per octave Preemp begins Before launching into a descrip- Columbia 78 300 6 1590 tion of the unit, let us consider Columbia 331/3 500 6 1590 briefly the purpose of a preamplifier Decca ffrr 400 3 3000 in R. C. A. 500 2.5 1000 a reproducing system. This done, Technicord 650 6 2500 we can deal with the design prob- Mercury 300 7000 lems more intelligently. It is worthwhile at this point to Our problem is, then, to use this It is our belief .that in any A -B consider the actual purpose of a pre- information to design a simple, in- test, if a listener finds two units (or amplifier in a reproducing system. A expensive preamplifier v e r s a t i l e two settings of a given unit) which preamplifier should bring the level enough to do its work of bringing a sound different, yet he has no par- of a device up some low -level pickup output up some ticular preference for either to standard. At to -then it this point in the system, switching standard level and, at the same time, is safe to conclude that neither is the to produce a nominally flat response correct answer. generally occurs. The output level of the preamplifier should be compar- curve from the program material. During a long period of experi- able to that of the other units, such Since a number of curves seem to mentation efforts were constantly as AM and FM tuners, so that no be in use, the standard single -net- made to obtain the actual recording appreciable change of main gain work preamplifier will not suit our characteristics. It was of course ob- control setting will be needed on needs. To do this, we place two vious from the first that if these are switching from one program source equalizers, one a low- frequency type available, the whole design problem to another, and all sources should be with five positions and one a high- is vastly simplified and most of the nominally flat at the point of switch- frequency type with four positions, cut -and -try method -which is cum- ing. in the circuit with an isolating tube bersome and time -consuming at best Rather careful compensation has between. We now find that by proper -would be eliminated. to be included in a preamplifier to choice of constants, we can comple- Such data are not easy to obtain, make records sound "right." Listen- ment all of the above curves either 63 Melchor St., South Boston, Mass. ing tests have evolved a series of quite closely or with at most a 2 db error, as Fig. 1 illustrates. Fig. I. Response curves of preamplifier with and without feedback. Gain Requirements Fortunately, pickup performance data are easier to obtain than record curves. We find that to bring. a I 9Ó á o W Pickering, Clarkston, or car- W similar p-,. tridge up to about 5 -volt level under . I average conditions requires a gain, I , LL in the flat portion, of about 28 db. A GE pickup will require nearer 40. 60 '- 10 1 (If we have about 5 volts at our _. WITH andi- ¡. 'a80;WITHOUT switch point, !! the AM tuner diode - e FEEDBACK !1 to deliver this -is being fed a signal ó 50 1111I g \11II11 large enough to minimize those dis- -CÌ¡Ì tortions which plague diodes at low

_LL levels.) 3 We want, further, enough extra ~ 40 1 jj IÌin!\\ gain to complement the curve which _ , 111ÌI::;s needs the most boost, and this re- _ quires about 30 db more The 20 gain. total is more than high -gain triodes l lin101111111110111111111 can supply without loss of quality . io , , . . , . . , . . , , . lea laoo 1 and without the feedback (with its FREQUENCY IN CYCLES PER SECOND attendant advantages) falling dan-

14 AUDIO ENGINEERING MARCH, 1949 4 o

A J B FLAT o o 2 E F 1, -3 N 31 G m -6 -10

-9 o H -12 -20 C K o

. , . . , 1000 ] 0000 200 , 0000 1000 10000 FREQUENCY IN CYCLES PER SECOND FREOUENCY IN CYCLES PER SECOND.

Fig. 2 (left). Effect of resistor in series with shunt condenser. Fig. 4 (right). Derivation of actual high- frequency roll -off curves from graphical (dotted lines) construction. gerously low at the bottom end. So combination, for the five curves. \1" power amplifier and speaker. we decide on a pair of pentodes. also use screen bypass values which We now have a high -gain, low- The 6J7 is an excellent tube for seem unnecessarily large until we noise, low- distortion, low- frequency- the first stage, having low hum and consider that we are bypassing not compensating preamplifier of simple little noise, yet it is inexpensive and a screen dropping resistor alone, but construction, but one which still readily available. In t h e second it and screen resistance in parallel. does not correct the upper end of stage, a 6SJ7 eliminates the grideap. Furthermore, we feel that it is de- the record spectrum. If we Applied We choose constants which give high sirable not only to make the ampli- t h e feedback approach here, we gain consistent with freedom from fier stable on the low end but also to would run into several difficulties: erratic behavior on changing tubes. achieve critical damping. This re- our gain when on the NAB -type We adjust voltages to meet our out- quires a 6 db per octave droop below curve would run perilously close to put requirements and to minimize the useful frequency range and on unity at the extreme high end, and intermodulation without feedback down to the point where the gain our feedback would rise appreciably, (as evidenced by d -c plate voltage approaches unity. with attendant disadvantages. shift vs. signal level). Note that the low- frequency turn- Further, there is no objection to a Operating the first heater on d.c. over selector switch is a shorting conventional losser in this applica- was found unnecessary; a variable type. Otherwise opening the feed- tion. We can feed it directly by the center -tap and variable positive bias, back loop between switch points re- pickup and its design is simplified as shown, suffice. Now we apply feed- sults in a sudden and extremely an- by being isolated by a tube. For the back to reduce the gain in the fiat noying rise in level -about 30 db! first we examine the NAB charac- portion to that desired -28 db in this The 10- megolun click suppressors are teristic, which is a simple 6 db /oc- case. We allow the gain to rise at a not merely gingerbread; the sharp tave rolloff, beginning at 1590 cps. 6 db rate by a conventional RC com- transients generated in their absence This calls for a simple RC network, bination. But we supply five such create extremely high peaks in the with a product of 100 microseconds; 01 + 300 v. 10 Meg J 1 FLAT each V 0114I o .0072 Ifrr ) 005. ° f 7 RCA d N 1.8 Meg 0 OED 6J7 I OUTPUT o o NAB 6SJ7 Fig. 3. Complete 00 J I schematic of pre- 51,000 20 amplifier. 1001 0 +300 v. 4700 u

18,000 -"VV\rQ

I I Oa d

AUDIO ENGINEERING MARCH, 1949 15 0.1 meg and .001 µf is a good com- lay a rule along this curve, we find -120 dbv, or about one microvolt. It bination. With too small an R, we its closest approximation is line is not possible with ordinary test need to figure in pickup resistance jgk, which has a slope of 2.5 db/oc- equipment to measure lower, which and inductance. Since these vary tave with respect to a new pseudo justifies the hum -bucking circuits with manufacturer, and we are de- turnover frequency which is about used rather than the d -c heater sup- signing a universal preamplifier, this 0.39 times the mathematical turn- ply with its attendant, expense and is not desirable. At the opposite or over. It is easily seen that if b and bulk. The one -microvolt figure was high -impedance extreme we may run c were farther apart, the realized attained in each case with the second into hum pickup and tube input slope would have been steeper, and 6J7 tried; the first, however, gave capacitance begins to cause some in this manner we arrive at the con- only about 10 db more, which is still trouble. stants shown in Fig. 8. in the excellent- performance bracket. A brief examination of the curve Now to the measured performance The RC time constants in the feed- produced by the above and all other of the preamplifier. About a half- back path are, however, rather criti- such networks shows us that at the dozen have been built using 10% tol- cal. It is not easy to measure a nominal turnover frequency we are erance resistors picked at random 1.8 megohm resistor with accuracy; 3 db below the original level, and at rather than selected for exact value. hence the following procedure was exactly one octave either side are 1 Three amplifiers were carefully followed. The amplifiers were as- db down from the respective as- tested. The best of the lot had 93 db sembled with parts out of the bin; ymptotes. The slope of the curve in- gain without feedback (100 pf across in one case four of the five constante creases at the rate of 6 db per octave. the first stage cathode resistor) and were correct, in another, three, as This slope is fixed in character and 30 db on the flat portion of the curve plotted curves showed. Examination cannot be changed; however, it can with feedback. The curves shown of the curves showed clearly which be stopped along its travel. Since we happen to be for the worst of the capacitors to change, and in which need other curves of less slope (2.5 three, as are the performance data. direction and amount to achieve the db for RCA, 3 db for Decca), they With a Ballantine model 300 meter intended result. can be obtained by stopping the 6 (0.5 meg) and a Dumont 208 scope Such an equalizer has been in use db curve at some empirically deter- (2.0 meg) as load, the maximum out- nearly a year in conjunction with mined point. put was +20 dbv (db relative to one an amplifier- speaker system which Suppose we insert a resistor in volt) -n peak -to -peak swing of 28 we confidently believe to be 3- 21/2 series with the shunt condenser to volts. At 1200 cycle turnover, which db from 48 to 13000 cycles and rea- give a second turnover two octaves gives maximum bass boost, the out- sonably free from transient defects. above the first -as in Fig. 2. The put with a 600 ohm attenuator across The one outstanding change that ap- asymptotes are the line a b c d ; as the input, and no further signal, was peared to coincide with the installa- would be expected, the actual curve -88 dbv. Since the gain at 60 cycles tion of the equalizer was that listen- falls 3 db below b and above c. The is 52 db this says that the hum vol- ers started, for the first time, corn - actual curve is ae /ghid; and if we tage referred to the grid is about [Continued on page 40] Leff: A complete audio amplifier with the versatile preamplifier described in the text installed in the upper left -hand corner. The two controls below the 6J7 and 6SJ7 preamplifier are the high- frequency de- emphasis and tweeter vernier gain control. The program level control for the amplifier itself is alongside the preamplifier controls. Right: Bottom view of complete amplifier, with the preamplifier wiring in the upper left -hand corner. The two controls are the high- frequency de-emphasizing control and the tweeter vernier gain control.

16 AUDIO ENGINEERING MARCH, 1949 \\ \ \I. \o York. flei. tor n,n.,,lr. in! hot peiln n , nl rag L.. k iii.t innn PII

nrndern ndllinn Jnllrir n Ondi t.e,md, I ii.tnni-

\\I. óuill bc N(':\. I h.i_n ,l I r I\I nJ 1\ nprr.ahni.

thi. Cunsnlo haunlle. In .1101111 npnt. .111.1 I1 ,,1. n e 6,n1ne l. sinueleanroua,. n indi, iIILenll, l .1 1114 .-1.1

\I)I)ITIO\ to the comprehensi\r line of A (w of these custom- Intilt installations are pic - standard studio -control equipment .0 L1 1ili r tured on these pages. They range from special to the induar%. R(..' sp i,eliies in do :iL iiiui equipment for medium -sire stations to complete and Imilding auelio- control installations to meet speech -input systems for the largest nel.vork the individual need: ul stations and networks. installai' s. These systems have he'll worked Speech -input . stems ul thi, tp ivre tailor -made out with the nations leading station and melwork ...with jn.l the right 1.1( dines for handling 'ers. I heq incorporate every conceivable all studio -control operations required by the in- facility for controlling program operations and dividual star reproducing high- lidedily sound. Se bled et64414,-- ~that ... a2e

\\'FAA. I)allas. I hi. ronlrril lon>111e-y\ith il.

de Iu\e andto ynipunnl ra, Llin-line) h11 ' I the n,,aster deskis one unit Id \\'1':1.1s up to date istudio setup. 1'Ilstmll-hllllt I,\' R(.;\ C plltr IIe\1h1h1\" lar Iliple prnllrrimnu11!

-.i1111dtallenll. 11r irille,1111,11IIl , ririlrril ill it) 111- puts tl, ó 0111! 111,1 uI.. Prenll ..\ilrllinl and complete 'lass. 11e, dines pro \ 1.1r11.

\\ \I:W. New York. 'Ellis ter [101 console -in \\ 's n1o,Lrn 7- studio lineup -is C11111 1111 hni11 by IWA. The console is 11.11111'11 IIII 1111 h .ide by i de lose .11111111 ey11ipn1eul racks. It has complete 1111 ililies 111r 1.0111111 111111 preset

.11 it, him! 11 7 studios Io It) out - oin! lìnes...and for leelling cue

Iron, .1111v eh.,mrel to ally studio.

WIPG -FM. Green Bay. One oI the speci.11!.- Illlilt studio n11tr111 ,a11.1/i1`C

111 \\IPM; F'l s . I-Stmhn 11 ,Lmrrlt - ,11.11111 -Luth h, RCA. r plete t ,11 h.rnoel operation ( \'I .1114I FNI),

.ilnllh.lne..us a lit' and I least

I any comhination..1 studios. re le lines, cueing and talkhack are provided.

. 4.: , (((/f((tiCfló . YY.'N,iii RCA

(ill-hill.). 5i.i1411 111 1..51. i.151515

\vI\II. 1 .boli aulluliun-1 u.1,1441 lnlill I15

\. I1 111.,5 1111. 1 0 1 op1111 ,111.11-151111111 11,151r111 ;11111,1..1111

.ul or i1111111.11ur1n1.) 11 1 11111. ,1,1111111.1 usi 4.. ri,1

. ,1. 1 11.. 11111 111 11_1141 !".111411.. \

I. I R1\111.

115,1. 111.1.1,.1 1111111 1nn!, all I ,.j¡': .1.1e 14i5_1. 11i11i', -'lt" 1Id1.11.

('It"z. N1,5 loa. II,

@r.441, .11 1,Ji1i1.1 11 11.,11,.1,111.

4,11,Ii1, i,,.b111.1r.,,1. 1 11.11.111 1,11111 115

la .\. C8.4414..1.4 - 1opo1 1 ir111í1. (011111i-11

K()?I(). S1.rlll.. 1111. 111,1.1. r 1111111111 11,11

í,51 11.1. 44.11 5i.i1111.) i. 111.1 111141 411 ti(11(i. 1,1..11,1511l, ,1111 111111 ,11.,,14.,.1 ' .b,114,5 .,.11.111. 111115,11-1,11il1 145 1,;(...\.

u111u1 q lor 111 ,n11i,1. .111,1 ,5 1111_1,1111_. (KOvI() - AvI. KO>IU I vI. 1111551,1, ,1141. -,1111,1_,11..5). RCA "tert-toii -med6 "qteed- iout cQnfiel2aemid to meet evn inditúkt tat,ni need

WIAL, Baltimore. The master control console and 6 de luxe audio equipment racks in WBAL's "World of Tomorrow" 10studio installation- custom-built by RCA. Control of seven program originating points extends switching facilities to any of 4 outgoing channels (AM, FM, audition, and utility).

RCA "Custom -Built" equipment service is available glad to do it. Or if your specifications are already to every AM. FM and Television station -and on al- down on paper. RCA will be glad to work from them. most any working arrangement desired. For example. Your RCA Broadcast Sales Engineer is at your if you want a station studio survey and a detailed service. Call him. Or write Department 407. RCA layout proposal, RCA Broadcast Engineers will be Engineering Products, Camden, New Jersey.

BROADCASTING, The Everything IS 0^e Equipment Source for

AUDIO BROADCAST EQUIPMENT et161.- RADIO CORPORATION of AMERICA ENOINEERINO PRODUCTS DEPARTMENT, CAMDEN, N. J.

In Canada: RCA VICTOR Company Limited, Montreal Fig. I. Compact, two section amplifier with control section arranged for mounting in small panel area.

C. G. McPROUD*

Part I -A new amplifier of exceptional performance especially designed for modernization where cabinet space is limited. Compact 6AS7G Amplifier For Residence Audio Systems

MANY AN EXPERIMENTER or audio enough to fit into reasonable firmly established, and any good am- hobbyist has the desire -and spaces. plifier must be designed to accom- often a definite need-for a Control facilities which may he mounted on a small panel space sep- modate them without the need for high- fidelity amplifier, but is at a loss arate from the amplifier. an external preamplifier. As is well for sufficient space to install it in an Considering these requirements sep- known, these pickups require equal- existing cabinet or piece of furniture. arately, the first is fairly obvious. The ization of the low- frequency spectrum, So far, many of the writer's amplifier reason for modernizing is to obtain a in addition to considerable gain to designs have been adequate for good better quality of reproduction. This make their output comparable to quality reproduction, but none was demands good components, and suf- that of a radio tuner. The micro- arranged specifically for use by any- ficient power to handle peaks without groove pickups are slightly lower one desirous of modernizing a repro- danger of overload. Since it is more in output in most instances, due ducing system because they were all economical and usually provides better largely to a lower level on the record laid out with a view to accommmodat- overall quality to use a high- quality itself. ing the components in a normal ampli- loudspeaker with a good reproducing Although not generally known, a fier arrangement. system, a fairly high efficiency is gen- conventional crystal pickup can be To solve any problem, it is first erally encountered. Most high -quality fed into an equalized preamplifier, necessary to recognize its existence-- speakers will provide plenty of volume and will often sound better than if the rest follows naturally. -For a for home use with much less than one used with a high -impedance input. modernization problem, the require- watt of average power although more As far as the frequency response is ments may be stated as follows: is necessary, of course, to handle the concerned, this is easily explained. Electrical: Around 5 to 6 watts of high - peak levels. Therefore, it is felt that A crystal pickup may be regarded quality audio power. five watts should suffice for practically as a generator of zero impedance in Switching to select standard and mi- any home system. It goes without say- series with a capacitance. An average crogroove phonograph pickups. ing frequency and two additional positions that response should crystal pickup, for example, has a for AM and FM radio inputs. cover the range from 30 to 15,000 cps, capacitance of around 1500 t<µf. When Sufficient gain and low -frequency and that distortion must be held to such a pickup is fed into a resistive equalization for low -level mag- an absolute minimum. The hum level load, it has a natural droop of 6 netic pickups. should be so low that no sound is audi- Separate high- and low -frequency tone db /octave below the frequency at controls. ble from the speaker in the absence of which its reactance equals the value To these may be added as desirable signal. of the resistance into which it feeds. features a volume control compensated Multiple Inputs Thus, it has a "turnover" frequency for loudness levels, and means for Practically every reproducing sys- of 500 cps when fed into a 0.2 -meg equalizing the levels of the various in- tem is used for more than one input. load. Now, while a crystal pickup is a puts so the compensated volume con- Since the advent of long -playing, constant -amplitude device and de- trol works at its optimum position and microgroove records, it seems logical livers a constant voltage into a high to avoid undesirable level changes to include an input for a second pick- resistance load up to the turnover when switching between inputs. up, with a single selector switch con- frequency (of the record) from a Physical: Amplifier and power supply small necting the chosen input source to disc cut with the normal 6 db /octave the amplifier. droop below the turnover, the low - *Managing Editor. Armo ENCINEERIyc Low -level magnet ic. pickups are resistance load causes a loss in bass

AUDIO ENGINEERING MARCH, 1949 17

+20 chassis, made from 7 x 11 x 2 stand- 5 ard aluminum chassis. The two sections are connected by a three -foot 11111 cable which carries all power and signal circuits except for the a -c switch 3 11111 line, which is separate. The a -c 2 .í111I 2 switch is not a part of the control 0 section, but is to be mounted at a 711111 convenient location on the panel. 1 3 IIÌi: Circuit Description III general, amplifier design pro- 4 gresses backward, first involving the -20 selection of the output stage, then 5 adding the earlier stages to provide sufficient gain to drive the output tubes. Because the 6AS7G has so w 20000 100 1000 10000 many advantages as a power output FREQUENCY IN CYCLES PER SECOND tube, it was chosen again for this ap- Fig. 2. Tapped high -and low- frequency tone control switches provide fixed plication, in spite of the fact that it response curves. is relatively hard to drive. response equivalent to that of a mag- previously described in these pages' It may also be said that the power netic pickup. But the preamplifier The level adjusting is accomplished supply requirements for this tube corrects for this loss, so the output 11y means of three 0.5 -meg potentio- are fairly severe since it draws a is again "flat" The voltage output meters, with the microgroove pickup rather heavy plate current. Normally, of the crystal is higher than that of having no built -in adjustment, since this necessitates a large power trans- the magnetic pickup, so the loss due the overall amplifier gain is designed former and one or more large filter to the low- resistance load may be to fit this input. If further adjust - chokes. However, one of the require- accepted readily. Since high -frequency ment is required, it may be accom- ments of the tube may be considered equalization is still necessary for the plished externally. an advantage-because it needs an in- crystal pickup, it is still necessary The amplifier, shown complete in put transformer, the output stage can is to add a resistor shunted by a capaci- Fig. 1, built in two sections -one be completely isolated from chassis tor in series with the high side of the is the output stage and the lower ground, thereby permitting the use pickup to make it workable with a supply, while the other is the control of a voltage -doubling selenium recti- with high -gain preamplifier, if wide -range unit, all the other stages. The fier circuit, as shown in the power sec- section is built on a standard reproduction is to be obtained. There- power tion schematic, Fig. S. This arrange- 5 10 3 while fore, this type of preamplifier is x x chassis, the control ment furnishes up to 150 ma at ap- is housed in a x 7 x 2 reasonably suitable for crystal pick- section proximately 300 volts from a 117 -volt ups. a -c line. The 6AS7G draws about 120 Most users want some tone con- 1 "Full -Range Loudness Control," Winslow, February 1949. ma, and an additional 30 ma is fed trols so as to be able to obtain de- Fig. 3. Schematic of power amplifier section of the two -unit amplifier. sired response curves. While the compensated volume control reduces tb need to a large extent, satisfactory 6AS7G reproduction of phonograph records T T2 demands some roll -off control, and also a sharper cut -off for particularly noisy records. Varying degrees of (-; NME4 = TO EXT 05 SWITCH bass boost are also desirable. There- fore, both low- and high -frequency C3 -e- tone controls are employed, provid- 125 R4 + ( - -d°o ing five curves for each as shown R3 5 xl 7500 X2 S+I in Fig. 2. These are step controls + + rather than continuously variable _.42a-.02b Ç2c_ +c4I_ 125 potentiometers because more suitable 0_. 40 curves are The low -fre- obtainable. T3 quency control provides a 5 -db droop Ry R6 6AS7G Htr 50 flat 0 at cps, a position, and boosts z 6e00 6800 of 4.5, 9, and 13 db at 50 cps. The high -frequency control provides a a 50 05b P boost of 6 db at 10,000 cps; a flat 05c 5a, position; a roll -off down 3 db at 4400 20 140T30 10 ; 5r3 cps and 8 at 10,000; an NAB roll - off down 3 db at 1600 cps and 16 at 10,000; and a cut -off down 5 db at 3500 cps and 21 at 10,000. Listenin_ tests have adjudged these steps to be desirable. The particular type of fully compensated volume control used is that

18 AUDIO ENGINEERING MARCH, 1949 Fig. 5. Schematic of the control section. through a bleeder for heater current Control Amplifier completely on their switches as shown of the three input tubes. Thus the 'l'ho control amplifier is of unique in Fig. 4. All resistors connecting to low -level heaters are energized by design, since three controls are ground are wired directly to the tube rectified alternating current. Con- mounted on the front apron of the sockets, and connections are made sidering the use of a push -pull output chassis, and one on the end, and with point -to -point where convenient. A stage, the provides capacitor sufficient the tubes on the rear apron project- resistor strip is mounted on the filtering for humless reproduction. ing away from the panel. The con- volume control, using the long screws The input stages require a d-c trols are arranged so the unit may of the switch assembly to hold it in supply which may be grounded to be mounted either vertically or hor- place. This strip carries most of the plate and decoupling resistors. e the chassis, and in addition, the izontally, thus being adaptable to al- 6AS7G heater must he energized. most any cabinet space available. The assembly of the control section Thus a small power transformer is The selector switch is on the end of in such a small chassis is somewhat used with a conventional rectifier the chassis, with an operating lever tedious, but there is plenty of room, ' and an RC filter circuit. The 6.3 -volt which extends through the panel. and the object of the whole amplifier filament winding on the transformer Also mounted on the end are the two was to make it convenient for mount- is used only for the 6AS7G, since the pickup jacks and the level- adjusting ing. other tubes have a d -c heater supply. potentiometer for the standard pick- Inverse feedback is used around up. The decoupling capacitor and the the last three stages, primarily to 1'he output transformer is massive two radio input jacks are mounted reduce the output impedance to a and occupies a large portion of the on the rear apron along with the minimum. The output transformer chassis area. The space underneath tubes, while the radio level- adjusting has 4, 8, and 16 -ohm taps, with the the output transformer is occupied potentiometers are on the "top" of latter supplying the feedback voltage. by the two 125 -µf capacitors on a the chassis. The power cable comes out Good frequency response, power, bracket; the channel-type, and push -pull of the end opposite the selector switch. phase-shift characteristics are readily input transformer is also under the To simplify wiring into the cir- obtainable with a transformer de- chassis, as are the coupling and line cuit, both tone controls are assembled bypass capacitors. The selenium [Continued on page 40] Fig. 4. Assembly of tone rectifiers are mounted on Bakelite controls on standard switches to provide units easily wired into the strips above the chassis, and are pro- control section. Left -bass control; right -treble control. tected by a perforated screen cover. The capacitors in the voltage doubler power supply-the two 125 -µf units and the triple 40 -,f unit used for cathode bypass of the 6AS7G -are insulated by cardboard tubes. All connections except the output are made on one end of the chassis: a 9-prong socket for the control section feed; the a-c line cord, fuse, and switch; and a small two -prong socket for a remote power switch which is in parallel with the chassis switch. This permits a pair to be run up to a panel -mounted power switch, thus eliminating any a-e circuits from the interconnecting cable.

AUDIO ENGINEERING MARCH, 1949 19'

Testing Hartmann whistle in parabolic reflector.

Experimental Ultrasonics

S. YOUNG WHITE*

Part I- Design, construction and operation of the Hartmann whistle.

THE SERIES of articles' on the com- quency range. On investigation, it equivalent of this high -power sound mercial application of ultrason seems that the design is quite com- source, there are several peculiarities ics aroused considerable interest plex and the operating principles hard of air coming out of an orifice that among various groups of engineers. for the average experimenter to grasp. must be reviewed for those of us who One reaction was a desire to do some There are also some difficulties in have forgotten the laws of fluid flow. investigation of the phenomena in adjusting it for optimum output. The basic jet is formed by a "thin 1, their own shops at home, so as to It is always a pleasure for an elec- plate orifice" of Fig. this being become acquainted with this odd tronics man to investigate some other merely a hole, usually considered to form of energy. One place to start is field and find his familiar problems be circular, in a plate so thin it is with a Hartmann ultrasonic genera- o f negative resistance, impedance assumed to have no effective dimen- tor, or whistle. sion. Air under pressure forms a jet The Hartmann design shown in as shown. the photograph was invented in 1927, There are two points to keep in and proved to be able to put out about mind. Since the air reaches the hole 6 watts of acoustic power in the range from the side as well as from the from 15 to 40 kilocycles, using as a AIR axis of the jet, there is a squeezing source of compressed air an ordinary UNDER action which rounds off the jet at PRESSURE one - third horsepower paint - spray tl-e orifice edge. The area of the jet compressor. With more power it is is about 66% of that of the orifice. capable of over 60 watts output when JET In Fig. 2 we see a conventional round- driven by a compressor of about 3 or ed orifice, where the sides merely fol- 4 hp. The device appears so simple low this line of natural flow. The jet that we could ask why it does not Fig. I. Thin plate orifice. Area of jet diameter is then 100% of the orifice . model sell for ibout $5 in the shops, = 66% of orifice. Max v = s.v. diameter. thus allowing anyone with a paint (13.6 lb. /sq. in. gauge). The second thing to bear in mind outfit to play with ultrasonics spray match, resonance and so on in a is that air cannot be emitted from in this fre- with this wattage and new form, but still responding to the an orifice at velocities higher than sonic velocity, in this case 1100 ft/ *% Radio Magazines, Inc., 342 Madison same treatment. The Hartmann whi'- Avenue, New York 17, N. Y. tle is a good example of a rather com- second. As you increase the pressure [AUDIO ENGINEERING, June, July, Nov., plex phenomenon quite understand- from zero gauge the velocity increas- 1947. Jan., Feb., April, June, 1948. Our able to an audio engineer, if put in es more or less linearly until at crit- supply of these issues is exhausted but electronic terms. ical pressure -in this case 13.6 lb/ will be reprinted later in these articles we reach q. inch gauge sonic velocity is book forni. Before the electronic - 1949 20 AUDIO ENGINEERING MARCH, reached. No amount of pressure will EXAGGERATED increase this velocity, but of course SIDE INJECTION Inure air will be forced through the orifice as at higher pressures it is -2D INTERNAL more dense. Fig. 3. Cross -sec- CROSSOVER DETAIL About a hundred years ago it was tional view of found that some such jets had a curi- whistle with cross- ous internal detail of crossovers, as in over indicated. Fig. 3. This was maximum when the REFLECTING velocity was sonic and the orifice was BOUNDARY designed to exaggerate the side in- LAYER jection, as indicated in the drawing. In 1927, Hartmann suggested that oscillation entirely, while a change that, since we are discharging com- the slopes of this internal detail re- from 80 to 100 requires little or no pressed air, a good deal of moisture presented positive and negative resist- adjustment of the spacing. At all forms on very part of the generator, ances, and that if a resonant organ times the spacing has a great effect so we also require a completely cor- pipe be placed in a negative resist- oil the waveform, but usually it can rosion -free assembly. ance region, oscillations would occur. be adjusted to give a fairly pure A little calculation shows that par- This is done usually as shown in Fig. waveform. ticles of dust or moisture coming out 4, with the cavity tunable over some To appreciate the difficulties, let us of the jet at sonic velocity have a range. So we apparently have a nov- design such a unit. We shall make it striking power of about 5 to 10 tone elty item that could be made of dur- as simple as possible, of the most eco- per square inch. It takes quite a alumin or perhaps brass, connected to nomical materials, and match it to a tough material to stand it indefin- a paint spray compressor, and provide conventional one - third horsepower itely. Let us see what we cannot use. 5 watts of high audio or ultrasonic paint spray compressor giving about Chrome plating is of no help, as frequency with which to experiment. 40 pounds pressure. By going to 90 it rounds the edges. Cyanide or other pounds pressure, the same unit will case hardeners usually require re- When Hartmann actually inserted deliver about 5 to 10 times greater grinding to establish the definite such a cavity he found that the air output, because only the spacing be- edges we wish, and when we break packed into the cavity and then blew tween the jet and the cavity needs the skin of a case -hardened job we whose section, out again in slugs to be changed. are not sure what we have, and it By making a few trial models with will probably rust quickly. (If we durai or brass, we find the edges of oil the unit to prevent rust, the oil the cavity and jet are critical in de- is scoured of in a minute) ... 18 -S sign. They cannot be feather edges, stainless steel is not tough enough. as too much of our output then forms A good material is Ohio Airdy- "white noise, "2 and if the generator a standard tool steel of high chrome is set for above audibility we do not content and, properly heat -treated, want to be annoyed by this hissing will show a compressive strength in' sound any more than necessary. By excess of 500,000 lb. /sq. in It is a blunting the feather edges to a def- little difficult to work, and it must, Fig 2. Standard shaped orifice. Area inite thickness of between one -half be sent away to be heat -treated, but of jet = 1000/ of orifice. and one and one -half thousandths, it is about the best material available' we can minimize the white noise. for the purpose. It will save time and we find edges money if the model is made in durai was diamond - About this time these viewed from the side, and its performance checked as long shaped. It was found the best effici- take quite a beating and erode badly and the as it lasts, and then a duplicate in ency obtainable was about 4 %. It the- in a half hour or so, generator we need the tool steel is made. oretically blows at any pressure above ceases to function. Evidently a material will this ero- 13.6 lbs. per square inch, but in prac- that stand Calculating Jot Six. much better. We also notice How we size? tice it is difficult to obtain oscilla- sion do calculate the jet We a table in the "Compressed tions below 20 lbs. pressure, and consult 2Random noise covering entire frequency which gives the cu- many refuse to blow at pressures be- Air Handbook" range being investigated, so called be- bic feet per minute for orifices of vari- low 50 or so. At 90 lbs. they are quite cause it forms a solid white pattern on ous size. We then ask the manufac- easy to operate and adjust, but at 30 an oscilloscope. are rather critical at some settings. Close -up view of the Hartmann whistle. The curve, Fig. 5, shows that the action is more complex than a simple organ pipe as the length of the pipe has a complex relationship to the 4 frequency. Greatest power output is developed when the cavity is from half a diameter to about two diameters deep. The frequency does not vary too much with pressure, but at low pressure operation the spacing between jet and cavity is quite critical, and a change of 25 to 30 lbs. might stop

AUDIO ENGINEERING MARCH, 1949 21 trol must be smooth, and a reference mark on it allows setting to a desired frequency. A cross-section view, Fig. 4, shows an exaggerated piston diameter. The spring forces it against the screw, and an enlarged end on the piston retains the spring and also aligns it with the cavity so it will not bind when being adjusted. Stainless steel drill rod, uuhardened, seems to stand the erosion all right, and in the model discussed is is D. This same unit will operate with full output of about a 1% hp compressor at 90 lbs. pressure, with no modification, except for spacing between jet and cavity. Onteking Operation Three instruments can well be used in this range, as well as several transducers. A simple and readily available combination is a Rochelle salt bimorph crystal from a new or broken phono- Checking waveform of ultrasonic whistle output. graph pickup, feeding an ordinary oscilloscope. The crystal should be turer of several compressors how The frame holding the two in line shortened by cutting with a razor many cfm they deliver and receive axially must be as transparent to blade to a length of about inch. not very definite replies. It seems that sound as possible, yet hold the parts h The response will be full peaks, with air under ideal condi- in very accurate alignment. must of standard It but it will give comparative output, tions the delivery into a certain load also allow the cavity to be easily slid and if we adjust the generator to emit is so much, but in actual field condi- forward and back from the jet, as a sine wave, the crystal will tell us so. tions the output may be rather widely the position for optimum oscillation different. Some responsible manufac- is quite critical. A PN crystal from Brush will also turers rate their product in cfm dis- work, a half -inch cube being suitable. placement, and we are free to choose The adjustment screw that allows If held 2 inches below the generator, our own percentage of air actually variation in the depth of the cavity the output will be as much as a volt delivered, which may be from 90% must permit the piston to cone flush or two, so ample trace on the scope with of as down to a lowly 60 %. A % -hp com- the edge the cavity, many is had. About the same reading will pressor at 40 pounds should deliver times the cavity eollects dirt that is be given if a parabolic reflector is about 2 cfm. That works out at about otherwise quite difficult to clean out. used, focussed on the crystal. a 42 thousandths orifice. Since com- Oscillations start when the cavity is One misleading effect is that if the pressors are single- cylinder affairs in about half a diameter deep, and con- crystals be unloaded, such as by a thin this range, a regulator should be used tinue for several diameters. A typical rubber diaphram under some tension, to smooth out the pulsations, so the tuning range is from 14 kc to 50 or they will give sine wave output on jet should be designed for about 35 60 kc, with maximum output of about white noise at their natural period. pounds actual operating pressure. 6 watts from 18 to 35 kc, a very use- This is pretty low level and should ful ultrasonic range. The screw con- not próve too bothersome. Because the orifice is not designed to follow the natural flow, some in- Fig. 4. Frequency is varied by adjusting piston. efficiency in volume delivered is to be expected, so a correction of about 20% is in order, giving us an orifice of about 44 thousandths as the actual size. Thus, for the resonant cavity de- I TO 1.5D sign, we arrive at a diameter of .044 BEST ABOUT I 25 inch. General experience shows that the diameter of the cavity should be slightly greater than that of the jet, PISTON and .062 is a standard drill size, so we make it .062., although a ratio of about 1.25 is optimum, which would call for a diameter of .055. Material DEFINITE EDGES would be the same. It should be ob- I vious that only that part of the as- CALIBRATED SCREW in the path of the WHITE NOISE - sembly directly SONIC high -velocity air must be hard mat- ENERGY erial -the rest of the assembly can (SINE WAVE) be any non- corrosive substance.

22 AUDIO ENGINEERING MARCH, 1949 A Boonton voltmeter is fiat to 200 kc and works well with these crystals, BO but the 'scope is more useful as it gives the peculiar wave forms you are able to obtain by improper adjustment of the generator. A Navy or Coast Guard long -wave 60 W receiver can be easily modified for N this use. Take out all but one tuned o 50 circuit and replace with wide band Fig. 5. Frequency amplifiers. Even one tuned circuit and power out- 40 gives too much selectivity for most put of cavity of z 6 MOS. varying depth. 30 Other Equipment Cavity diameter ¢ 5 .062 A source of compressed air, filters - ". 4 and regulator and gauge are necessi- 20 3 ties. About 30 feet of hose will allow the compressor to be some distance 10 2 away. although enclosing it in a sound- proof box is also worth while. If you go downtown to buy some air com- 20 40 60 60 100 120 140 160 pressor fittings please check that CAVITY DEPTH - THOUSANDTHS you have enough for the right kind DIAMETER ..062' of connectors and so on, as they are Start the compressor and adjust sure. The same effect can be had if often different from standard pipe the jet to about 35 lbs. pressure. Have you hold your hand out fiat with the thread fittings. t he jet exposed on the end of the fingers pressed tightly together and Starting the Gnratr hose. You will now find that the play the jet along the crevices be- If you are sensitive to high level cross -over type of jet will drive at tween the fingers. But for widest sounds at the threshold of audible resonance anything with a crevice in controllable range, squeeze the thumb pitch, have some cotton handy to it. Point the jet at the edges of the and forefinger together and play the stuff in your ears, as there is always pages of a closed book, and tunes can jet into the joined surfaces. By vary- a tendency to tune the whistle down he played on them by squeezing the ing finger pressure we can play from into audibility. hook together so as to vary the pres- [Continued on page 44] ,9naGlpma in atLdio E

LEWIS S. GOODFRIEND*

Details of an audio engineering course to appear serially in this magazine.

AUOIO ENGINEERING 16 that branch a group having no fixed background order, but acoustical couplers and of engineering that deals with other than a strong interest in the impedance -matching devices should the generation, transmission, field, it is best to start with the meth- be left to a later time when they and hearing of sound. It is based on od of hearing and the operation of may be compared to their electrical acoustics, psychology, and electronics, the ear, and it is at this point that equivalents. It is here, however, that and when the study or application of the present series, "Problems in Aud- such topics as the energy and inten- any one of these phases is neglected io Engineering," will begin. The study sity of sound waves should be treated, or over -stressed, as electronics often of the ear includes application of the and the definitions of terms such as is, the result is of questionable value. decibel and the general background displacement, amplitude, rms, mean, In selecting subject material for a of units of sound power, including octave, frequency, period, as well as course of study in audio engineering the Weber -Fechner law. the fundamentals of musical instru- it is therefore necesary to comer all Once the student thoroughly un- ments, should be carefully discussed. three phases. It is not difficult to find derstands the phenomenon of hearing, two possible points of departure with he will find it possible to analyze with Architectural Acoustics the choice determined by the back- ease many of the seemingly complex The next logical step is the con- ground of the students. In planning problems of audio. A survey of the sideration of the general field of a course for a college of engineering next important phenomena, the meth- architectural acoustics followed by a it is best to begin with material re- ods of sound generation and trans- detailed study of decay, reverberation, lated to prior courses in physics and mission in an elastic medium, may liveness, sound insulation, and a com- vibrations which are stressed in such begin. It is at this point that care prehensive anaylsis of the spectra of an institution. The starting point in in the selection of material must be music, speech, and noise. Problems this way is fixed at the generation of exercised, or the remainder of the of correcting existing acoustical con- sound waves, and their transmission course will be completely devoted to ditions of buildings may be consid- to the ear. For courses to be given to the minutia involved in the theoreti- ered here, but design of new auditoria cal considerations. A close examina- *Stevens Institute o/ Technology, is in 341 Hoboken, N. !. tion of point and dipole sources [Continued on page AUDIO ENGINEERING MARCH, 1949 23 WMGM Master Control Equipment Design

M. E. GUNN*

Technical data on a modern, high -power, broadcast station installation.

At.TI1011U11 THERE are many- services a stutiuu break interval (sometimes meat is mounted in standard cabinet and fuctions performed by mas- by the operation of a single switch) racks nvI,iclt are bolted together to ter control, probably the most im- he can execute comparatively complex form a single unit as .shown in Fit/. i. portant is the switching of programs switching schedules in a minimum of The switching system is composed of (remote or studio) to outgoing lines. time and without the chance for error six identical sets of controls,. relays, In addition, monitor facilities are re- that would exist if each studio had and light- (one set for each output quired for offices and lobbies. Moreover, to be switched independently. This channel t. The counter, approximately remote line terminations with associ- system is flexible in that channels 13 feet: long, provides working spare ated equalizing networks are necessary, can also be operated individually if and gives all the operating conveni- and telephone lines must be main- it. is necessary to switch a channel ences of a desk -type control system. tained for communicating to oper- at some time other t.Iinut a quarter- The counter top is covered with burn - ators handling remote programs. Test hour interval when must program proof niicarta and the edge is trimmed gear should be available for making changes are tnntie. With tla improved with 4 -inch aluminum moulding. The measurements of frequency response. performance obtained, and consider- counter assembly- is fastened to the noise, and distortion, of outgoing ing that there is less likelihood for racks by means of heavy angles, thus programs. operating error, this type of pre-set making it unnecessary to have any At W t(; M, multiple output switch- system is a sound investment. legs for support. Cutouts in the ing is accomplished by a master con- At the present time there are six counter edge serve as convenient trol pre -set system which performs studios in operation at \1'111;. and locations for telephones. all operations by means of relays. these, as well as three reunto pro- All master control rn.ks are mount- 'l'his system permits the operator to gram circuits, etlll he switched to idle ed flush with the wall. 'thus. spree at set succeeding up the dispatching or all six outgoing ch annels. In ad- the top and ends is closed off and a circuits ahead of time. Then, during dition. there is one spare program door is provided at the left end. input which may be used as all leading to the area in back of the *Audio Engineering Section, Engineering emergency- input or may be reserved racks. Three LC -1A monitor speakers Products Dept.. RCA Manufacturing Co., for future expansion of studio facili- are built into the wall above the racks Camden, N. J. ties. and are splayed to a degree to give All of the master control equip- optimum listening advantage. Al-

Fig. I. Master Control Room layout for WMGM showing pre -set switching system in the center and six racks of de luxe associated audio equipment on each side.

N M s

ea II 01 I-- ..: v Fig. 2. WMGM Master Control Block Diagram.

AUDIO ENGINEERING MARCH, 1949 25

Fig. 4 (left). This view of the Studio A console shows how panels and doors may be opened to provide easy access to all components. Compartments with doors opening to the front contain terminal blocks.

Fig. 3 (below). View of de luxe Studio A control console illustrating convenient location of all controls.

though this installation was made in a room having a concrete floor, what might have been a problem of running conduits and cable troughs to the carious racks was en solved. RCA cabinet. racks have 4 -inch removable hases. These bases were re-

uaocwl :nul the racks mounted on and a monitor circuit. A VIT meter. I io. II :n tavni:oicntly normalled two -inch steel channels which were which is also fed from the dividing to tro hanks of mechanically inter - laid on floor. These channels extend network, indicates the signal level to loeked push keys. The common out- across the room in a continuous line the line. put of each bank of push keys feeds (with a 6 -inch offset for the center Each monitor circuit contains a a separate remote amplifier circuit section). A false floor of wood is laid BA -1A amplifier with a bridging which enables the signal to be ad- flush with the top of the 5 -inch chan- volume control input. This prevents justed to the proper level for feeding nels in back of the racks. Space under line disturbances in the monitor sys- the switching system. The input to a this is adequate for all the required tem from reaching the regular pro - third remote circuit is not connected conduits and cable troughs. grant channel. In addition to the six to any switching device, but is termi- On the wall in back of the racks regular output channels there are nated on jacks. Bridging transform- are located separate junction boxes six emergency circuits, each consist- ers feed the remotes to all studios for telephone, power, signal and audio ing of a bridging transformer and a so that they may be handled in con- circuits. All circuits coming into mas- BA -3C amplifier. Both ends of these junction with a regular studio pro- ter control are cross- connected to circuits are terminated on jacks, thus gram. It is impossible to select the terminal blocks in these boxes. Each providing complete stand - by pro- same incoming program on both studio has a block for audio and a tection for all channels in case of switches at the same time. This re- block for signal circuits with the same any emergency. quirement is necessary to maintain arrangement for leads for all studios. the proper load impedance and - Remoto Pickup Circuits to pre both at the master control junction elude the possibility of mismatch The handling of incoming remote a box and at the studio end. This makes to the line. and is accomplished programs involves two considerations. by for ease in tracing and remembering having one set of switches wired one being to maintain communica- in 'Iri'uits. series wth the other. tion with announcers or operators at An amplifier circuit using a BA -4C Output Channel Switching remote locations. This is done with is provided to feed cue to the remotes. C.birring to the block schematic, a talking circuit usually referred By means of a selector switch. any Fig. _, there are ten inputs to the re- to as an "order wire." The other con- one of the monitor buses may be fed lay switching system with a possibility sideration is to receive the incoming to this remote cue amplifier. of feeding six output channels. A remote on a separate line, equalize transformer couverts the 600 -ohm in- it if necessary, and route it either Monitor System comiut circuits to 1JUobuis for switch - direct to the master control switch- 'there are three monitoring circuits, in;:. 'these are terminated by a 150 ing system, nr to a studio (depend- ouch consisting of a BA-4C amplifier ohm resistor. This termination is ne- ing on how the schedule is set up). and an RCA LC -1A high fidelity cessary. since all output channels are \C\Í M has GO incoming remote speaker. Input selectors to these bridging and several (up to six) chan- lines. 30 of which have individual amplifiers are connected to a monitor nels may take the saine program. Each l ('A type 5G-C equalizers. Three type bus system consisting of 16 circuits output channel consists of a bridging Ill': -1B variable equalizers are sup- with isolation amplifiers. Monitoring transformer, a master gain control, a plied to correct the characteristics of points available are the ten switching BA -3C line amplifier, and a dividing lines other than those which are inputs and the six outgoing channels. network which feeds the regular line permanently equalized. Twelve of To provide an additional check on 26 AUDIO ENGINEERING MARCH, 1949 the over -all channel circuits, a bridg- it possible to connect the echo cir- duct opening to keep dirt from the ing transformer is connected to the cuits to any desired studio. pedestal out of the ducts. terminals where each channel out- Two BA -4C amplifiers are bridged Each pedestal has three compart- put terminates in the rack. These six across output channel No. 1 and are ments. Doors to these compartments outputs appear on a six -position, used for feeding speakers in 15 of- are flush -fitted and each is supported mechanically- interlocked push -button fices. by a continuous piano hinge, as seen switch, the output of which can be Ample test equipment is supplied to in Pig. 4. In the left pedestal there switched to the input of one of the provide the station with all the neces- is one large compartment with a door monitor amplifiers to provide a final sary facilities for measuring fre- opening to the inside of the desk. program check. Jacks are also avail- quency response, noise, and distortion There are three shelves in this com- able to provide means for additional of any program circuit. Tie lines to partment on which are mounted checking and monitoring. the various studios make it possible eleven preamplifiers. two power sup- to pipe studio circuits to master con- and several line and bridging Other Features plies, trol to utilize this equipment. Sparc transformers. Amplifiers and power A beat - frequency oscillator, feed- line and bridging coils, as well as supplies are of the plug -in type. ing six BA -3C amplifiers, provides fixed pads of various losses, are pro- Therefore the removal of these units override time tone signals which can vided and can be used as an aid in for any reason is a simple matter. any regular program or announce- making measurements. Another smaller compartment, open- ment on each of the six output chan- ing to the inside, contains two cir- master Studio Equipment nels. Relays operated by the cuit breakers and pilot lights, a switch the tone A deluxe studio desk, Fig. 8, was clock provide "on- -hour" for emergency relay voltage and n to provide in a single unit heats. designed meter for checking the amplifier all operating facilities for the con- Another feature at WMGM is that tubes. Two selector switches pick up trol of Studio A, which is one of one of the studios (Studio "E ") can the metering terminals of these ampli- two auditorium type studios in the interrupt the regular program on one fiers. WMGM was intended or all output channels and feed those operations. It The third compartment contains that this studio console should offer channels directly with a special an- terminal blocks for connecting to pre- the maximum in fidelity, flexibility, nouncement. This by- passes the external a -c and d -c power circuits reliability and operating convenience. set selector system and normal oper- as well as incoming microphone lines. Appearance was also to be of utmost ation is not restored until control is This placement of terminal blocks importance considering the prestige released by Studio "E." There is, how- facilitates trouble -shooting when it is of the ever, a cutoff switch in the master station. necessary to check external circuits The desk is constructed entirely of control room which can take this to the desk. Needless to say, the desk steel and completely replaces con- control away from the studio. To pre - installation was less of a problem than ventional rack equipment with its elude unwarranted program inter- with the terminal blocks in some associated console by providing a ruption through misuse of the Studio out of the way place. "E" channel- operate keys, power to housing for all the amplifiers, power The large compartment in the right actuate the override relays is fed to supplies, relays, etc. These components pedestal has 3 shelves, contains six the studio only by order of station are mounted and housed in two ped- booster amplifiers, two program ampli- management. Lights in all studio estals which in n conventional type fiers (one regular and one emergency), control rooms as well as master con- of desk would be reserved for drawer one power supply, and a studio moni- trol indicate when any channel is space. Each pedestal has a 2" x 6" amplifier. interrupted by Studio "E." opening in the back which is con- tor Amplifying equipment for two nected to an air conditioning duct A second compartment contains a echo rooms is supplied. Each equip- in the wall. This provides enough small jack field for all speaker cir- ment consists of a BA -4C echo speak- cool air to prevent abnormal tempera- cuits. Since these are high level cir- er amplifier, and a BA-1A echo micro- ture rise due to heat from the ampli- cuits, this location affords the isola- phone preamplifier. Tie trunks make fiers. An air filter is placed over the tion desired and keeps all loudspeak- turrets Fig. 5. In Studios C and D, a standard RCA 76 -C consolette is used in conjunction with auxiliary custom -built side (jack bay at right -and sound effect filters, echo controls, cue selector and supervisory lights at left). Space is provided for turntables at each side of the operator's position. er jacks out of the main jack field. only occasional adjustment, -o they a separate booster and master gain The studio speaker volume control need not be part of the main panel. control. The outputs of these gain is in the voice coil circuit and is Access to each side compartment is controls are combined by n matching located in this compartment for the by a hinged lid, flush -mounted in network to feed a single channel into same reason. The balance of space tho top. n BA -3C amplifier. A spare channel is used for the storage of patch cords Producer's Desk is available for emergency service. A 'lien they are not in use An added feature of this studio key is provided to feed either channel The third compartment contains control equipment is a producer's to master control. audio terminal blocks and speaker desk, Fig. 6, which is styled similar A three -position echo mixer circuit relays as well as a volume control for to the control desk, except it has no with bridging transformer inputs and studio headphones. The terminal over -all control turret. The left end a BA-1A booster is supplied. Rever- blocks are placed so that external of the desk has a pedestal exactly the beration characteristics may be ap- wiring connections are easily made. same as the pedestals on the main plied to as many as three microphone Conduits which carry wiring to the console. The right end fastens to the channels by patching from a pre -amp terminal blocks come up into the main console so that it becomes part output multiple to one of the bridg- terminal block compartments and of it. In the left pedestal are mounted ing transformer inputs. The BA -4C are stubbed about two inches above two auditorium PA speaker amplifiers for feeding this signal to the speaker the floor. and one client's speaker amplifier, in the echo chamber is located in mas- The sides or ends of the desk ped- both of type BA -4C. This compart- ter control. The echo microphone pre- estals which are fastened with con- ment also has connections to an air - amplifier, which is also in master concealed screws were removed during conditioning duct. trol, feeds the signal back to the studio the time the desk was being wired to The producer's controls consist of n on a tie line. As this is a 600 -ohm provide easy accessibility to all ampli- studio talkback microphone with asso- circuit, it must be patched into an fier plug terminals. eiated "operate" switch and an inter- unused mixer position to be combined Mounted on the desk top is n con val tinier used principally for timing with the normal program. Two sound - iinuous turret which extends from shows during rehearsals. These pro effects filters are supplied to obtain a the left of the operator around to his ducer's controls are mounted in a wide variety of effects in conjunction right. Since the height of this turret small turret placed on the desk. with the reverberation facilities. is only 39 inches above the floor, ade- Program Control Facilities Another three -position mixer cir- quate visibility into the studio is All mixing. amplifying. monitoring cuit with bridging inputs is provided enjoyed by the eontrol operator while and special -effect facilities required to reinforce certain microphones for seated at the desk. to produce and control a program are the benefit of the studio audience. most The essential controls are contained within the control console. Microphone reinforcement is often in mounted on a panel directly front A twelve -position mixer which per- desired by certain radio artists as well. of the operator. This panel is hinged mits simultaneous mixing of ten The output of this mixer system and access to at the top for any parts studio microphones and two incoming associated booster amplifier feeds two requiring maintenance. Two slopes to remote lines is incorporated in the BA-4C amplifiers, each driving an this control panel provide maximum design. The first six mixer circuits LC -1A speaker concealed in the pro- operating convenience. are controlled by one program key and scenium. Gain of the PA amplifiers There is a jack bay on each side each of the other six mixers has an may be controlled by a person in the of the control operator, each bay individual key for cutting the circuit back of the auditorium, thereby assur- containing 99 pairs of jacks. Access in or out. This feature is especially ing the proper speaker level for any to jack wiring is gained by removing advantageous for the control of large size audience and at the same time a panel in the back of the turret. programs using an orchestra with a preventing acoustical feedback. Us- Each jack bay turret is joined to the multiple microphone pickup. It is pos- ually it is necessary only to reinforce center panel turret thus providing sible to cut in single microphones for dialogue, sound effects, vocalists, an- enclosed space for mounting addition- announcers or vocalists while fading nouncers, or special features and not al equipment, such as PA volume the entire orchestra down with a sin- an entire orchestra playing on the controls, echo mixers, sound effects gle control. stage. controls, etc. These six controls require Each bank of mixers feeds into There are three input possibilities Fig. 6. Closeup view of producer's turret as used in studios A,B,C, and D. to the monitor amplifier feeding the control room speaker and a studio speaker. The input is normally connected to a dividing network in the output of the program amplifier as n regular monitor. A key transfers the input to a rotary switch for selecting a cue for the studio from any of 16 monitor buses in master control. The studio talkback circuit is connected to the monitor amplifier through a relay Nvhich disconnects either the eue or monitor circuits. Two microphones are provided, one on the console control panel and one on the producer's desk. Each is connected to the talkback circuit by a key which operates the talkback relay. When either talk- [Continued on page 39]

28 AUDIO ENGINEERING MARCH, 1949 Acanto/ fay DmDhroem Product of UV Research

The "650" Broadcast Dynamic

Smoother, Wider Range Response Extremely Rugged Service ACOUSTALLOY is the amazing new non- metallic diaphragm developed by Electro -Voice engineers and utilized so effectively in E- V dynamic microphones. l Its remarkable characteristics create a new concept of performance. It makes in possible higher output level and smoother The "645" wider -range frequency response. It is prac- Broadcast Dynamic tically indestructible ... withstands high humidity, extreme temperatures, corrosive effects of salt air and severe mechanical shocks. There's a better E -V microphone for every need. It"rite for information. ELECTRO-VOICE, INC., BUCHANAN, MICH. Export: 13 East 40th St., Now York 16, U. S. A. Cables Artois

NO FINER CHOICE THAN

The "600 -D" The "CARDYNE" Dynamic Mobil -Mike Cacdioid Dynamic The "635" High Fidelity Dynamic

AUDIO ENGINEERING MARCH, 1949 29 PENDING actual distribution (April) of ically, shows up the slightest added noise the Victor 45 -rpm record a large EDWARD TATNALL CANBY* (where noise was drowned in the shellac amount of somewhat futile discus- hiss), the relatively soft and scratchable sion is going on as to (a) which system, material, above all the static charge that 45 or 33, is better technically, and (b) sticks the grit on -all this means that which company is the hest justified (or we'll have to treat plastic, small- groove the most damned) in its position. It is so rapidly, back and forth, back and forth, records with extreme care if we plan to over this last that the general public is the subtle sense of timing one develops, keep them for a reasonably permanent very hot and bothered, not to mention anticipating nervously the inevitable ap- library. I suspect that a good many record the trade. This department has some priv- proach of each side's end simply by the collectors will continue to patronize the ate views but it seems at this point an sense of elapsed time, so that an extra - shellac market for these very reasons. excellent idea for all of us to put aside long side has one on edge with tension, Engineers at this point are busy with the question of blame entirely, as a prac- waiting for it to end -these familiar dis- slide rule or equivalent arguing as to whe- tical consideration. Not a thing can be turbances, almost unnoticed after years of ther RCA or Columbia has the better done about it now anyway. Nor is there conditioning to short records, suddenly groove speed for optimum performance, the slightest hope that any of us will be turn out to have been of vital psycholog- taking in all factors.. The question would able to get to the bottom of the highly ical significance in the listening process, seem a fairly simple one, and yet it is complex inside negotiations and maneuv- now that they are vanished. Play a whole, over just such simple matters that the erings that have been going on these many unbroken, LP side for yourself, of a fam- scientific mind can get most het up! years past in respect to new -type records, iliar piece, and see. The long- playing rec- Again, I've run into what seem to be di- before any public announcement was made. ord is, for all lovers of music -at- length (as rectly contradictory statements here. The I have heard statements of responsible opposed to those who can enjoy only short question is interesting. My impression is, officials on both sides; they emphatically slices) an absolutely fundamental advance- at the moment, that LP loses to Victor - do not agree, even as to points of plain ment, worth all the troubles, major or groove in its inner portion, but being a fact. The -discrepancies aren't worth in- minor, that may crop up. This is no plug much larger record -the 10 and 12 inch vestigating nor is there any use expecting for an individual record company but a sizes- it has a considerable outer area agreement, for by now this whole schism heartfelt and purely subjective reaction, in which the groove speed is better than has become such a- matter of personalities, and you will find it widespread right now. Victor's or as good. (The Columbia 7 inch record of company prestige, justification and ra- f will be curious to see how Victor's quick - is another matter.) Columbia tionalization, that it would take a congres- action changer stacks up in the hearing claims that, even so, its inner grooves are sional investigation and more to establish against this competition-but let that far better than those of the standard 78 the whole story in objective terms -and wait until April. record. As always, this department dodges to what purpose? The troubles of course do come. I all mathematics in favor of the ear. So Rather, let's concentrate on the facts of haven't had LPs long enough to be con- far, my ear definitely confirms Columbia. the present, on the merits and demerits scious of wear, though my sapphire (Asta- I have yet to hear an LP record that was of the divergent systems -there's plenty tic FL-33) is supposed to he better in noticeably bad at the inside, or even not- of room for argument from now until this respect than the metal LP points. I iceably different between inner and outer doom,,i.ty and, for that matter, not a little am occasionally disturbed by a good many grooves; whereas 78 rpm records with poor fun it. the arguing for those of us who ticks and swishes not supposed to be heard inner grooves are as we all know painfully are in the sound field. (A lot of us, strictly on LP. Pressing trouble. But two much common even in the best circles. (Ouch!) But in any on the Q.1'., of -course, are taking a cer- more serious troubles are scratching and case, note this well: that though tain ill- disguised pleasure in the compli- dust. Scratches are painfully easy to make technically and on paper the 45 rpm cations of the new three -speed era!) and their sound is magnified by micro- record may well show a better over- It's a good moment, then, with LP groove. Merely pulling the records from their all potentiality than the 33, the slight dif- well established and the Victorgroove rec- cardboard casings seems to do damage. ference in quality attributable to this factor will ord still unmarketed, to take a bit of stock Even finger marks may sound in the play- be far less noticeable to the ear than many grosser on the LP records, as I'm finding them in ing. As to dust, the records. so far, have differences in the qua( ities of the constant everyday usage. As a musician arrived dusty, and in typical plastic fash- original recordings. Of this I - am quite sure. Whatever the technical and this I can't say too strongly-I am ion have immediately picked up all the an- swers, I continue to be astonished at the more than enthusiastic about the long - free dust available in the nearby air. I've music comes forth playing achievement. Space-saving, yes. been using a damp soft cloth -even so, that from the LP record and in the long But it is hard for a non -musician to real- the dust clings and the rubbing of it in- run, in spite of difficulties, I find it clearly ize bow much the unbroken performance to the grooves is a dangerous business, preferable to most 78 rpm music, from which of a longer work adds to musical enjoy- wet or dry. Blowing or shaking is quite it has been dubbed! So it stands, pending ment. I wouldn't have believed useless, I've even taken to flowing tap trial of the it myself. Victor record. The LP record is something more, it seems, water across the record to wash out as Though that record itself isn't with us than merely a longer record. It takes rec- much dust as possible without rubbing. yet, I feel that some points made in ad- orded music right out of its own field, into A nuisance. vance by RCA are at least open to ques- the "actual performance" feeling of a radio It is right here, I suspect, rather than tion, if I interpret rightly. One point, as or a live concert; The difference is start- in matters of technical quality, that the I get it, is the implication that records at ling. The constant 4.-minute breaks greatest trouble with both LP and Victor - (how- 331/4 were tried by Victor and not accept- ever short) of the old system, manual groove records will be found for most of or ed by the public. There can be no possible with changer, the intense awareness us collectors. These records just can't be of the comparison between the Victor Long Play- progress of the pickup across the record, treated as casually as shellacs, in spite of their unbreakability. The small, close ing record of 1933 and the present micro - 279 W. 4th St., New York 14, N. Y. groove, the quiet surface which, paradox. [Continued on page 88] 30 AUDIO ENGINEERING MARCH, 1949 Here's the Recorder You asked for!

The best features of Presto's dual motor gear drive with the overhead mechanism and turntable of the famous Presto 6 -N.

Es, engineers have often asked us for a I compact, economical yet high -quality recorder. Now you may have it in the Presto 66-G for standard and microgroove recording. Here is a unit ideally suited and priced for the typical broadcast station or large transcription manufacturer. List price, Standard Model, $996! ($70 additional for microgroove.) Here's perfection in total speed regulation and very low mechanical disturbance, thanks to the standard Presto dual motor gear drive. Here's high -quality recording, too, for the 66-G, of course, includes the Presto 1 -D cutting head. You'll find 66-G equal to the most exacting recording tasks when used with suitable amplifiers such as Presto 92 -A recording amplifier and 41 -A limiter amplifier.

FOR HIGHEST FIDELITY ...IT'S PRESTO DISCS Microgroove, even more than standard recording, demands a perfect disc. The answer is Presto. For, sixteen years ago, Presto made the first lacquer -coated discs ... and today Presto discs are first in quality. READY NOW: Magnetic Tape Recorder Presto will show its new super quality magnetic tape recorder at Booths 25 -26 at the T.R.E. Show, UJJ March 7th. Be sure to see it!

RECORDING CORPORATION

Paramus, New Jersey Mailing Address: P. O. Box 500, Hackensack, N. J. In Canada: WALTER P. DOWNS, LTD., Dominion Sq. Bldg., Montreal WORLD'S LARGEST JIA.vt.r.ICTDRF.R OF I.VSTA.VTANEOUS SOUND RECORDING EQUIPMENT AND DISCS

AUDIO ENGINEERING MARCH, 1949 31 NEW PRODUCTS

NEW SCOTT SUPPRESSOR of radial projectors. The Hypex flare The Cardinal Iras substantially Hat formula gives improved acoustical per- response front 30 to 10,000 cps. Output New changes in the output transformer formance, particularly at the lower fre- and chassis finish of the H. H. Scott 210. quencies. With sound distribution over a A Laboratory Amplifier with Dynamic complete circular area, this projector is Noise Suppressor have resulted in sub- intended for installations where stantial coverage improvements in its performance of relatively large areas and suspension and appearance, without sacrificing any tI'nm the ceiling are desired. of the compactness and fitte design that characterize the unit. ISOLATION TRANSFORMERS Three isolation transformers, with 50, 150, and 250-VA capacities' respectively, have just been announced as new catalog items by Chicago Transformer Division, Essex Wire Corporation. 3501 W. Addi- son St., Chicago, 18, Ill. Designed for dual purposes, they are suitable either for t 1 t a Ijusting high of low line voltages to operate radio, television, and other equipment on a normal 115 volts, or 12) promoting safer, more efficient servicing or experimental work level is -62 db. Recommended load im- on electronic gear by isolating chassis pedance, S meg. grounds from line grounds -- particularly Somewhat less universal but also a con- vertible type is the Astatic Velvet Voice Microphone. Case and handle lift from a The new oversize output transformer circular, desk -stand base for hand use or provides remarkable freedom from distor- attachment to floor stand. The Velvet Voice tion and reduces hum level to 86 db be- model will be recognized by many as one low maximum power output under normal of the most popular Astatic products in operating conditions, the actual hum pow- crystal and dynamic types. The same er level being only 0.05 microwatt. Such smooth, even response that prompted the a rating is generally achieved only in name of the original units is claimed for equipment manufactured for broadcast the new ceramic model. Frequency re- Ilse. sponse of the Velvet Voice Ceramic also A new anodized aluminum chassis elim- is 30 to 10,000 cps. inates tarnishing, and is extremely dur- The Model "QC" Pickup Cartridge with able against the rubbing and chafing of ceramic element is announced as offering constant use. The 210 -A's functional design is ac- useful in eliminating shock hazard on centuated by the massive transformer, and AC -DC television sets. Besides providing the ella --i- finish provides a much sleeker a standard 115 volts, the secondaries of cl ppea ra II I. these transformers will also supply 125 or 105 volts for use in locating faulty set SOUND PROJECTOR components. Complete description and An important addition to the line of prices on relperst- Hypex projectors designed and built by CERAMIC- ELEMENT MIKES ,lint startc'l through the Asiatic production lines is the new Cardinal Micro- phone with ceramic element, a multi- purpose, compact unit streamlined for hand -held use like an e'^ t s n. t felt padded back lets it lie flat on desk or table, where it may be talked across. Accessories include a base that serves as a desk stand; an adapter for attachment to all conventional floor stands; a hang - a new level of up bracket for mobile communications, physical ruggedness, in addition to its other advantages. It has etc. The heat -immune feature of the cer- a frequency range of 50 to 10,000 cps, amic element is of obvious importance in a needle pressure of one ounce. the latter applications, due to high tern - Immediate availability on all three Jensen Manufaiuring Company, is the peratures of car interiors in summer products is offered by the manufacturer. new Model VR -241 ST -789 Hypex pro- months. An off -on switch adds conven- jector, the first of the "Three-sixty" series ience to the Cardinal's wide utility. [Continued on page 341 PROFESSIONAL DIRECTORY

C. J. LEBEL AUDIO CONSULTAIT Custom -Built Equipment Winston Wells 370 RIVERSIDE DRIVE NEW YORK 25- N. Y. U. S. Recording Co. Designer and Consultant Acoustical and Electronic Research 1/ 1121 Vermont Ave., Washington 5, D. C. 307 East 44th St. MU 4-3487 PRODUCT DESIGN INSTRUMENTATION RECORDING STerling 3626 PSYCHO ACOUSTICS SOUND New York 17, N. Y. E1ECTPO'IED:CA, SUBMINIATUIIF AUDIO

32 AUDIO ENGINEERING MARCH, F949 aCtua This ls op.oN.FNN 5 RECORDING perf orrnance

When you can secure the quality of results shown Db. Ú 0 ö ó 0 00 00 in these graphs, can you afford to use any record- ol 0 0 0 0 0 ing equipment that does not approach such a standard? . +g

On the basis of definite performance, the 0 Maurer 16 -mm Recording Optical System - the 5 only postwar designed equipment of its kind on FREQUENCY RESPONSE CHARACTER STIC the market - is unrivaled in its field regardless OF GALVANOMETER USED IN MAURER of price. MODEL 10 RECORDER II And the Maurer 16 -mm System has already been selected by two of the four major radio net - works for their television requirements. D5 ó ó ó 0 0 0 N r6 -8 in

O Anticipating a demand for finer quality of recording, including the higher frequencies, the Maurer -5 Recording Optical System was designed to pro- -10 FREQUENCY RESPONSE OF PLAYBACK duce an extremely fine line image that makes ON MAURER FILM PHONOGRAPH WITH APPROPRIATE EQUALIZATION IN RECORDING possible the recording of frequencies bevy and -15 10,000 cycles, with very low distortion. The galvanometer of the postwar Maurer Model 10

System is tuned to 12,000 cycles. This is the model *For those who may have been educated to believe that such a result is not possible with 16 -mm film, we shall be glad to demon- that has been sold to the trade for two years. strate that it not only is possible, but practicol commercially NOW. _mauiir

"III, Professional '- J. A. MAURER, INC. Motion Picture Cameras and Recording Equipment for the Production of 37 -01 31st Street, Long Island City 1, N. Y. Industrial, Educational and Training Films

AUDIO ENGINEERING MARCH, 1949 33 THE TURNER MODEL 22 NEW PRODUCTS pag, .0 LP RECORD PLAYER ATTACHMENT A new LI' record player attachment has been developed which fits all types of existing record players, manual or automatic, without requiring installation.

Full information and detailed literature may be obtained by writing to Amer- ican Microphone Co., 370 South Fair Oaks Ave., Pasadena 2, Calif. Time - tested general -purpose crystal or dynamic microphone AUDIO PROBLEMS 'Iron, page 231 The most popular general purpose microphone on the market. The Turner Model 22 has an exceptionally and studios should be left until later when the associated prob- smooth response that appeals to discriminating users yet electronic lems can be included. the price is moderately low. A great favorite with ama- Only after establishing a firm foun- teurs and widely used in paging and call systems, record- dation in the first two phases of audio ing, and general sound work indoors or out. Fully shielded engineering is it worthwhile to begin to prevent r -f pickup. Distinctive modern styling and rich u general study of the applications of satin chrome finish. Equipped with full ninety- degree electronic devices to problems in audio engineering. This study should tilting head and quick -change removable cable set. not include any material on electronics itself, but should result in a set MODEL 22X CRYSTAL of specifications for various units of high quality humidity protected crystal in mechanical shock proof electronic equipment needed for optimum audio results. Included should mounting. Response: 50 -9000 c. p. s. Level: 52 db below 1 be a study of optimum conditions for volt /dyne /sq. cm. List $20.00 pick -up, transmission, and reproduction of sound, and an analysis of the MODEL 22D DYNAMIC meaning of high fidelity. It will be necessary to review the featuring high quality Alnico magnets in well balanced acoustic fundamentals of electronic compon- circuit. Response: 50 -9000 c. p. s. Level: 24 db below 1 volt/ ents, basic circuits including equaliz- dyne /sq. cm. at high impedance. ers, amplifier theory, amplifier opera- 200, 500 ohms, or high impedance $25.50 tion, and the basic principles of trans- 50 ohms. List 23.50 ducers, but before going on to amplifier design, a more complete study of transducers must be made. To do this it is possible to use either dynamic analogies or classical electro- mechanical theory. In view of the excellent treatment o f dynamical analogies by Dr. H. F. Olson in his book bearing that title, it is possible TURN TO TURNER FOR SOUND PERFORMANCE to do a thorough job on this subject and one which can be related easily to electronic circuit theory. Once the operation of transducers is under- THE TURNER COMPANY stood we must make some revisions 929 17th STREET N. E. CEDAR RAPIDS. IOWA in our specifications for the electronic u n i t s which were discussed above. The study of amplifier design may then be undertaken. Licensed under U. S. patents of the American Telephone and Telegraph In the work on transducers the Company and Western Electric Company, Incorporated. Crystals licensed under patents of the Brush Development Company. subject of musical instruments, aeons-

34 AUDIO ENGINEERING MARCH, 1949 tical impedance - matching systems, and resonant systems should be included, and comparisons should be "Equalizes 'em all ! // made with their electrical equivalents. While electronic equipment is an important tool of the audio engineer, it is not the only one and should not be weighted heavily. Electronic engineers are available who have far more knowledge of their field than It the average audio man will require, is no longer necessary to use a separate equalizer for each pickup. The 622 Position so Six Equalizer, usable that the highly complex problems with any and all modern pickups, involving mounts on your tran- transient response, feed- scription table in place of your present equalizer. You back, and servo systems should be left can now experiment with various pickup cartridges for advanced study in the field of knowing you are getting the best available performance audio or electrical engineering. These from each. Both lateral and vertical transcription arms items and their application and effects can be connected and selected without switching - by simply using the proper should be noted, however, and some setting of the 6- position control knob. A Micro -Groove arm may also be added. This Fairchild simple examples should be included Preamp- Equalizer precludes obsolescence; frees one preamplifier; provides for cuing and monitoring; in the course. eliminates low level hum problems; and is an investment in economy. Write for complete details. Sound Transmission Systems When the study of electronics has FAIRCHILD PROFESSIONAL TAPE RECORDER been completed it will be possible to examine complete sound transmission systems involving microphone pickup, transmission by electronic equipment, and reproduction of the amp- lified signal at remote locations. Here, an investigation of audio facilities for sound reinforcement, broadcasting, and recording may be made. This should include a review of the requirements for such .facilities, the practices normally used in the industry, including the vu, measurement equipment, and the types of measurements normally made, along with The Fairchild Professional Tape Re- nicer controls of starting, their significance. A well- stopping, spot- rounded corder is the only top quality equipment ting, editing, etc. 7' or 30 inches per course may include, if time permits, designed from the start to deliver the second operation may, of course, be a detailed review of the problems in- ultimate in performance at a tape speed included for special applications. volved in of 15 instead of 30 inches per second. the specialized phases of New and advanced audio engineering, theory and design Nothing has been left undone to make which covers the have resulted in performance which ex- this the finest professional tape recorder. special requirements of hearing aids ceeds the requirements set by the latest However,despite its performance which of all types, recording equipment, spe- proposed NAB specifications and for- we believe exceeds that of any other cialized forms of audio- frequency merly thought possible only at 30 inches equipment regardless of price, it is modulation per second. No compromise has been being sold at the lowest figure our anti- such as used' in FM, tele- made in meeting the most vision, exacting re- cipated production will permit. Cur- and pulse time; articulation quirements forsignal -to- noise, frequency rently, orders are being scheduled for testing, and so on. However, there response or minimum distortion limits. delivery in approximately 30 days at its may not be time to cover many of This means double the continuous re- present low price of $2,750. Details are these topics, and in this event the cording time, half the cost of tape and available for prospective users. student should be given a list of references, or better still a complete MICRO-GROOVE RECORDING .. . bibliography covering them. Are you aware that Fairchild Synchronous Disk Recorders and Transcription Arms are handling the One of the most important subjects rigid requirements of recording and reproducing Micro - Grooves for in audio engineering is the design of the most critical users? Write for detailed information. auditoria and studios. In covering the material on their design, there are LIP SYNCHRONOUS Sound -on -Film many ancillary problems which the audio man must be prepared to han- Synchronous disk recording and play- Used in making "Louisiana Story", one dle. These problems include lighting, back for ùse with motion pictures of the top ten movies of 1948! Write heating, ventilation, and seating. Un- and television is available with the for details. Fairchild #539 Portable Disk Recorder. less certain limits are placed on the architecture of the structure it may be acoustically perfect, but useless for audio purposes because of the . psy- We're chological or physical discomforts at the forced upon the audience. The artists I.R.E. who perform in the studios are subject to the same considerations. Table I shows briefly two possible 154TH STREET AND 7TH AVENUE, WHITESTONE, NEW YORK AUDIO ENGINEERING MARCH, 1949 35 methods of arranging material for the course as outlined above.

TABLE 1 Jloalinv Action! Hearing Definition of sound -structure of the ear -mechanism of hearing -char- for all TV Cameras acteristics of the ear- Weber -Fech- ner law- decibels -pitch scales - musical sounds- articulation-intel- "BALANCED TV TRIPOD ligibility. Pat, Pending Sound Waves Definition of terms -plane wave mo- 0,1" tion -the wave equation -energy in This tripod was engineered a plane wave -i n t e n s i t y -point and designed expressly to source -dipole source-is t r i n g s, meet all video camera re- pipes, and plates- musical instruments- speech. quirements. Architectural Acoustics Decay of sound- reverberation- Previous concepts of gyro treatment of enclosures -insulation and friction type design have -liveness, articulation, intelligibil- ity. been discarded to achieve Sound Spectra absolute balance, effortless Music-speech-noise. operation, super- smooth tilt Requirements for Electronic Devices and pan action, dependabil- Microphones - amplifiers - loud- attenuators -filters a n d ity, ruggedness & efficiency. speakers- equalizers -high fidelity. Components Below: Circuits and Components - equalizers- amplifier 3 wheel portable theory operation- distor- dolly with balanced -amplifier TV Tripod mounted. tion, noise, isolation. Dynamical Analogies Components- analogies -Ilse trans- ducer group- ear -filters -resona- Complete 360' pan without tors -musical instruments-iniped- ragged or jerky movement is ance matching systems. accomplished with effortless con- Amplifier Design trol. It is impossible to get any- Theory-practice-feedback-trans- thing but perfectly smooth ients. pan and tilt action with the Sound Transmission Systems "BALANCED" TV Tripod. Review of requirements -conditions Quick -release pan handle adjust. of pick up -audio facilities- repro- duction practice merit into desired equipment- -vu- locks position measurements- recording systems - by operator with no "play" be- audio- frequency modulation -hear- tween pen handle and tripod ing aids. head .Tripod head mechanism is Design of Auditoria and Studios rustproof, completely enclosed, Requirements- acoustical design- never requires adjustments, lighting-heating-ventilation-seat- cleaning or lubrication. Built -in ing. spirit level. Telescoping exten- (For engineering colleges the first and sion pan handle. second groups may be reversed.) Write for further particulars This article is an outline of the fundamental considerations in the selection of material for a course in CAf11ERA ECJUIPI11EI1T C. audio engineering. There are other 1600 8ROAOWRY nE W YORE CITY possibilities, b u t this outline has proved effective in the author's course W A N T E D at Stevens Institute of Technology. Western Electric Vacuum Tubes, Types 101F, It is hoped that the material will be 102F, 272A or B, 310A or B. 311A, 313C. of value both to instructors interested 8 323A. 328A, 329A, 348A, 349A, 352A. in preparing courses in audio and to 373A, 374A. 393A, 394A, 121A Ballast Lamps. the audio neophyte who would like Box 100, Audio Engineering. to study audio, but does not know where to begin. SECURITY W A N T E D W. E. Carrier Telephone and Carrier Tele- graph Equipment and componente. Filters, RECORD REVUE DS repeating coils, transformers, equalizers. [Irons page 30] Type CFI. CF2, H. C, and other carrier groove LP. The old record was quite in- equipment, telephone and telegraph repeat- adequate in quality, since it compared un- NOW ers. Box 101. Audio Engineering. favorably with equivalent 78 rpm repro- 36 AUDIO ENGINEERING MARCH, 1949 duction of the saine recordings. (I made comparisons at the time.) But above all, it used a standard groove, and the necessary compromise between length of play and quality was impossible from the start BEFORE -the first records were poor in quality; NEVER the latter ones, improved, ran barely eight FEATURES or nine minutes a side. Two standard sides, METER MULTIPLIER compared to a maximum of six on the INA V.U. present LP. No stigma can be attached to A VAILABLE this failure- equipment was inadequate all along the line then and the effort was a STRAIGHT futile but highly enterprising and progres- FIVE STEP sive one. Nevertheless, there is no possible "T" CIRCUIT comparison between the old record and the present LP development. t-.b, _ ,J 13/4" DIAMETER The other point I question is that, as ONLY a-.:SIMMEIMMG' I understand the argument, RCA is con- tributing to standardization in the indus- "OFF" try by offering a record and player ex- IN ATTENUATOR POSITION: pressly designed for each other. Stand - Terminals pair of ardization -yes, on RCA lines; but hardly 1. Extra of V.U. separate use standardization in the usually accepted for Meter. sense, which means an agreement between ,'T "Network completelycomp many parties on what is almost inevitably 2. from line disconnected a compromise between divergent view- and meter. points, divergent necessities. Whether it is Victor or Columbia that is acting uni- laterally is an undecided question. TWO STANDARD RANGES: Recent Recordings ATTENUATION to V.U. 0 (tmw) +i6 1. 4 V.U. steps Hindemith, Quartet in E flat (1943). and OFF in Budapest Suing Quartet. V.U. and 2. +4 to +20 Columbia MM 797 (3) V.U. steps OFF in 4 Here is a fine example of wide -range recording of four stringed instruments. There have been a number of Budapest SPACING: Quartet albums since the war, all wide - CONTACT adiacent steps range, but often rather badly done from 303 between the acoustic viewpoint. The instruments are seemingly too close and sharp, the The ingenious electrical- mechanical design liveness not live enough. This one (per - of these new type C35 V.U. Meter Multi- haps it is the music itself) has a fine, live plier Attenuators provides five step Straight sound, but still is nicely sharp and edgy. T performance in a control size normally The quartet seems big and round, as it limited to ladder and potentiometer circuits. should be. The music is not too difficult - increases it is solid, uncompromising, "pure music" A pair of extra terminals greatly -that is, without extra -musical effects, the utility of this unit, since in the OFF story, etc. But after a few hearings it position the V.U. Meter Multiplier network comes out friendly and rich to the ear, is automatically disconnected from the line with easily recognized themes, treated di- which it normally bridges, and the V.U. rectly and simply. Meter- completely isolating both. Rachmaninoff, Rhapsody on a Theme of As illustrated in the circuit at the left, the Paganini. V.U. Meter is connected to the auxiliary Art ur Rtihinstein; Philharmonia Orch., pair of terminals on the Multiplier when in Susskind. the OFF position, thus enabling the meter RCA Victor DM 1269 (3) to be used for volume indication on another This is a rip -snorting set of v,ria- line, for tube checking and other purposes. tions for huge orchestra and huge piano, Use of additional V.U. Meter Multipliers a late work of Rachmaninoff but hardly any what is normally called "modern ". The permits a single meter to be used for catchy tunes in some of these variations number of lines with each line isolated from have turned up as themes for radio shows, all others. The size and technical features of which'll give an idea of their category. this new unit suit it ideally for use in Rich as a chocolate malted. (with whipped consolettes. cream and nuts), expertly made, fabu- lously difficult to play, entertaining to listen to, but in the long run pretty empty Prices delivery of this unit as described or music -considering the number of notes! and to meet requirements avail- This is technically the top performance, as modified your with beautiful piano and orchestra; there able on request. Address: Dept. A -39, are other RCA versions by Rachmaninoff Shallcross Manufacturing Company, Col - himself and by Moiseievitch -the latter lingdale, Pa. most likely the best musically of all. Beethoven, Egmont Overture. Boston Symphony, Koussevitsky. RCA Victor 12 -0288 Brahms, Academic Festival Overture. Boston Symphony, Kousseevitsky. RCA Victor 12 -0377 Weber, Jubilee Overture. Minneapolis Symphony. Mitropoulos. Columbia 12891 -D hallcross AUDIO ENGINEERING MARCH, 1949 37 Mendelssohn, Ruy Blas Overture. well by the dissonant Copland piece San Francisco Symphony. 111onteux. (though musically I prefer the Concert 9ninoducfng RCA Victor 12 -0657 Hall Society recording by Leo Smit of A whopping group of overtures, each the same.) The Schumann work is sym. on a single record, each one split in the phonic in the sense of being a big, broad middle! All of these are separate works, showy work, unlike the more personal and written for special occasions or as intro- intimate piano music that Schumann most ductions or incidental music, all are tune- often wrote. The last etude is one of his ful, brilliantly -ended. Egmont and Ruy best known piano show pieces. The Cop. Blas are more in the tragic vein, Jubilee land sonata is dissonant, angular, quite and Academic Festival in the triumphant. harsh, but the sheer sound Copland gets All of them will make a fine show on out of the piano is interesting to most your big phono outfit. The two Boston re- ears, as well as the strong rhythm and cordings are Victor's best pre -ban, with clean, unmuddy construction. good highs, fine brass and cymbals, a Milhaud, Le Boeuf sur le Toit metallic brilliance, considerable distant - ( "The Nothing Doing Bar ") (1919). mike confusion and blur that, however, Minneapolis Symphony, i Iitronnulos. goes very well with the music. The Min- Columbia MX 308 (2) neapolis Jubilee is closer, wills a sharp LP: ML 2032 (One side 10 ") wide -range sound, relatively deader acous- A piece tics-a bit too dead. Terrific cvnsbals, bigtsl& amusing right out of the early flapper days pure and brass. Perhaps the best of all is the San -corn, simple, but so ingeniously Francisco Ruy Bias (it is decidedly the dressed up musically and instrumentally that it's a very finest performance). This RCA West - grade Coast recording is big and resonant like high vegetable. Serri- popular sound- the Boston records but softer textured, ing tunes, served with plenty of old -style brass, faintly dixieland, an with better detail work, a broader, round- dlots of outer perspective. landish dissonance. It was put on as a wild stage show (with Jean Cocteau) in The Model 102 Contact Heartbeat Copland, Piano Sonata (1941). Leonard Bernstein, piano. 1920 -the famous Paris joint was ap- Microphone, possessing high output parently named after the show, not vice RCA Victor DM 1278 (3) level and uniform frequency response. versa. The LP version is backer) by a Sturdy but lightweight aluminum housing Schumann, Symphonic Etudes. Alexander Brailovsky, piano. thoroughly worthwhile performance of one is acoustically treated to reduce feed- of Ravel's nicest works, the Tombeau de RCA Victor DM 1272 (3) back and external noise. Couperin, a collection of short daneh If you want a fine cross section of movements. Useful for detecting heart and other Victor's biggest and best piano recording, Debussy, Prelude a l'Apres -midi d'un Faune. physiological sounds, or for these two albums will do the trick -and experimental Ormandy. purposes. you can triangulate by adding the Victor Philadelphia Orchestra. Columbia 12891 -D (I ) For further information write Horowitz "Pictures at an Exhibition" album. Victor's piano is peculiar to Victor, A new, wide -range recording of one MEDICAL ELECTRONICS COMPANY no question about it. A huge, triumphant, of the most popular orchestral works on concert -hall sound, tremendous in over- records-but thinks to abnormally low- P. 0. Box 3541 Cleveland 18, Ohio tones, richly clanging. It is particularly level music, the widened range doesn't do suitable to the Schumann album, and does too much good. This is an example of the kind of music that suffers more in the wide -range playing -plus hisses that spoil its magic-than in a restricted -range playing that cuts out all highs, but leaves DESIGNED ESPECIALLY FOR the music free of distractions. 99 musicians out of 100 would prefer it without TELEVISION MANUFACTURERS* the highs. Try especially the beginning and ending. The best effect is with a cutoff of around 3000! On LP this recording may be something else again: little hiss to mar the tonal edge. But as long as it is pressed on shellac it must remain a "low- fidelity" piece. Beethoven, Cello Sonata in A, Opus 69. Pierre Fournier, cello; Artur Schnabel. piano. RCA Victor DM 1231 (3) Most people shy away fast from cello music, but here's one case where, if you like Beethoven, you'll like the cello. For once, the piano part in this cello-piano collaboration is given its proper value - in fact, the piano is actually stronger than the cello in the mike pickup (as, of Model 13837 CHOKE Model 5678 POWER TRANSFORMER course, it is in the live state, though most 5.5 H., 225 ma. DC. 70 ohms Primary- 115 volts 60 cycles engineers make the cello sound like a ten -foot monster and the piano some tink- resistance. Size: 21/2" x 214" x Sec. No. 1 -800 volts CT, 225 ma. DC. ling miniature in the background!) The 3'/a "- Weight: 23 lbs. Sec. No. 2 -6.3 volts, 8 amps. reason for this excellent balance is per- PRICE -quantities of 500-$1.68 ea. Sec. No. 3 -6.3 volts, .6 amps. haps the presence of one of the greatest Special quotations for Sec. No. 4 -5 volts, 3 amps. Beethoven pianists alive, Artur Schnabel. Nothing a larger quantities. Sec. No. 5 -5 volts, 2 amps. like big name to raise the dbs. In any case, the resulting sound is ab- Size: x x Welglit: 11 *Changes in specifications will be 4" 5" 4 %4"- lbs. solutely first-rate. This is a suave, easy- made to meet individual manu- PRICE -quantities of 500 -$5.72 ea. going piece with nice broad melodies. - facturers' requirements. Special quotations for larger quantities. little of the hectic and the explosive that turn up in some Beethoven. PEERLESS ELECTRICAL Hamlet. Laurence Olivier in excerpts from the film. Music by William Walton; Phil - PRODUCTS DIVISION harmonia Orch. Mathieson. 6920 McKinley Ave., Los Angeles 1, Calif. RCA Victor DM 1273 (3) 161 Sixth Avenue, New York 13, N.Y. Though the speech here is perfectly Fraser & Hansen. 301 Clay St.. San Francisco 11, Calif. Exclusive Export Agent intelligible, the recording does not speak

38 AUDIO ENGINEERING MARCH, 1949 too well for the present state of sound - on -film in England, as compared to disc recording. This oomes "direct" from the sound track of the flint-trouble might be in the copying. Whatever the reason, the HERE IT IS! tonal range is conspicuously less than in the fine British recording we usually hear today, the voice is a bit tinny; nothing to bother anyone but an engineer. The excerpts are wonderful for those who have The New Somerset seen the film; not so good for those who haven't, because Olivier naturally acts for the eye (the camera) as much as for the ear, and minus the picture itself his speak- NOISE SUPPRESSOR PREAMPLIFIER ing part, all on its own, seems rather colorless and inexpressive. Even so, if you are a Shakespeare reader you will find this most absorbing, and the music (several sides' worth) is excellent, as movie music goes.

WMGM Master Control [from page 28] back switch is operated, the control room speaker is disconnected and the studio speaker is turned on. When- ever the program line switch is operated, the power circuit to the studio speaker relay is broken, thus preventing talkback while the studio is feeding master control, During these periods, a talkback microphone booster is connected to headphones on the stage. These may be used by an an- nouncer or a musical director for taking instructions from the booth during a broadcast. Also, as these head- Accomplishes a high degree of noise reduction - maintains phones are normally in the monitor natural brilliance and realism - essential overtones are repro- circuit, a musical director can hear duced at all volume levels. the program as it is fed to master control. One BA -4C amplifier is pro- Introduces no unnatural tonal qualities in the reproduction. vided to feed program material to a Can be used with most existing record players and FM or AM clients' booth which overlooks the tuners. studio. Installation and operation require no technical skill. Supervisory lights on the console are automatically controlled by the SPECIFICATIONS: pre -set switching system and indicate to the operator when his studio\ has Power supply - 115 volts, 50 -60 cycles, a. c. been pre -set as well as when his studio Frequency range - 40 +0 15,000 c.p.s. has been switched to an outgoing Gain - .01 volts input produces .8 volts output to volume control of channel. When the operator closes his .25 to I megohm. Input sources magnetic or crystal pickups, and FM or AM detector program key a light in master control - output. is energized showing that the program Tube complement 2- 6SL7GT, I- 6SK7GT, I- 6SJ7GT, I- 5Y3GT. circuit is complete from microphone - 7" x 9" x 2 to channel output. Size of chassis - ". Facilities for Other Studios Also supplied in combination with a high quality power amplifier The facilities for studio "B" are for custom and commercial installations. essentially those for "A" similar to For broadcast and other exacting applications, special designs are but the remaining studios are equip- available. ped with standard RCA 76 -C con - solettes as the nature of program in Exhibited at L R. E. Radio Engineering Show, Booth these studios is not as complex as in "E" Grand Central Palace, New York City, March 7 -10 Studio "A" and "B." Paten's Pending In "C" and "D," auxiliary equipment consisting of a jack bay, echo controls, sound -effects filter and a 24- position cue selector is supplied. This SOMERSET LABORATORIES, INC. equipment, shown in Fig. 5, is built into two turrets with sloping panels, 1701 Palisade Avenue, one turret located on each side of the consolette. Union City, New Jersey Studios "E" and "F" do not have a

AUDIO ENGINEERING MARCH, 1949 39 "See our Exhibit Booth #210 at the IRE jack hay or a sound- effects filter. How- cathode bypass for Va are located in Show in New York March 7th to 10th." ever, Studio "E" does have the chan- the power section. nel override controls mentioned pre- The 6AS7G circuit is similar to viously. YOU CAN TELL THE those previously employed, with the A producer's desk and control tur- 600 -ohm 5 -watt resistors in separate QUALITY OF THE PLUG ret similar to that in Studio "A" and circuits, the 500 -ohm potentiomete "B" is furnished in both "C" and "D." serving to balance plate currents, and BY THE EQUIPMENT Acknowledgement the three heaters in series being connected between the arm of the balanc- IT CONNECTS The design of the above station 4 facilities has resulted from combining ing potentiometer and the negative the experience of 'WHOM engineers side of the supply circuit. The 600 - with the engineering and manufactur- ohm value is used in the cathode ing resources of the Radio Corporation circuits because of the drop across of America. All the equipment is of the heaters. The 7500-ohm resistor the latest design to assure the station bleeds the additional 30 ma for the control section heaters. high standards of performance, de- pendability and service. Subjective listening to this amplifier has indicated excellent performance, but since thorough measure- 6AS7G ments are not yet available from the Amplifier testing laboratory, they will he pre- Litwin page 19] sented next month in Part Jr. along signed for feedin a speaker or a with details of chassis layout and 500/600-ohm line, but it is difficult wiring. A complete list of components to obtain optimum performance from will be furnished to anyone desiring. a transformer designed for both types them. Address your request to Ai i i, ENIIINEHRINC, of output load. Consequently, the 342 Madison Ave.,'N wtw output transformer has only one out- York 17, N. Y. 'nit winding covering three speaker impedances. Phonograph Preamplifier Control Section [from page 16] The three tubes in the control section actually constitute five stages. paring the music to the original Vt is a dual triode in a conventional rather than to some other reproduc- RCA microphone with P3- CG -1l$ Plug and P3 -42 Receptac on P -41b ape- peramplifier circuit, with feedback ing equipment with which they were dal curved mounting base in Radio Station XHJof the Mutual Network in Hollywood. equalization to supply turnover fre- familiar. quencies of 350 and 500 cps. One Even though the curve of a par- The Type "P" Series is wide- section of the input selector switches ticular record is not known, a little ly recognized by radio stations and sound tech- the pickup, or grounds the first grid. listening experience enables one to nicians everywhere The second section varies the turn- select quite readily the proper equal- as not only the over frequency, and adjusts it to 350 izing characteristic; indeed, in the standard, but the cps for microgroove case of many records, leading series of recorda. The only one set- microphone con- third section connects the amplifier ting sounds at all satisfactory, oth- nectors. Promi- to the phonograph level -adjusting ers being very obviously wrong. Oc- nent among its many desirable qualities potentiometer at the output of casionally a record turns up for is the patented latchlock which provides the preamplifier in positions 1 and 2, which no settings will provide any . positive engagement and requires only the slight pressure of the thumb for to the AM and FM potentiometers illusion of realism. release to disconnect. It will not pull in positions 3 and 4, and to the pre - After having lived with this pre - apart accidentally. amplifier through a roll -off circuit in amplifier for several months, we feel Stocked or available from such radio position 5 parts distributors as Hughes -Peters in for microgroove records. tempted to conclude somewhat as Dayton, Specialty Distributing in Atlan- Thus the long -playing records are follows: The input data, upon which ta, Lew Bonn in Minneapolis, Almo Radio normally reproduced on the position the whole design was based is cer- in Philadelphia and more than 250 others. 2, the "flat" settings of the tone con- tainly in error by much more than 2 For full information on the Type P. ask trols. Victor for Bulletin P0- 248... And for prices and Decca ffrr records db in certain frequency ranges and RJC -2... Address Department C -109. reproduce best on position 3 of the on certain recordings. The probable high- frequency control, Columbias on error in over -all equalization in the position 4, and exceptionally noisy next record played will very likely I 5 C( 1915 records on position 5. The treble con- be well over 3 db, which is about the trol is numbered counterclockwise. maximum deviation between charac- the bass control clockwise. teristics obtainable with the forego- Qaaaoai The two tone controls are designed ing circuits. This says that further to work together and into a grid with progress is impossible or unwise un- no resistance loading, as is the volume til more reliable input data is on JIEV2,[2 control. Since feedback is introduced hand. at the stage ahead of the driver, the The finished product is compact. volume control is placed between simple to construct, and inexpensive. 3209 HUMBOLDT ST., LOS ANGELES 31, CALIF, the two sections of V2, the first sec- It does not demand critical toler- IN CANADA & BRITISH EMPIRE: tion acting as a cathode follower. Vs ances nor particularly careful pyhsi- CANNON ELECTRIC CO., LTD., TORONTO 13, ONT. is triode connected, and is shunt fed cal layout. It will accommodate any WORLD EXPORT (Excepting British Empire): FRAZAR & HANSEN, 301 CLAY ST., SAN FRANCISCO with the coupling capacitor in the current low -level wide -range car- cathode leg. This capacitor and the tridge and correct a n y current

40 AUDIO ENGINEERING MARCH, 1949 known or alleged response curve. Its hum, noise, and distortion content ore a lot better than most commercially available equipment. and Awn THESE 3 NEW PRODUCTS AUDIO TECHNIQUES a [from page 13] AT TERMINAL REK-O-KUT "CHALLENGER" PROFESSIONAL RECORDER tion arises during musical transmis- 12 "2- .speed recorder with precision over- sions, where views of the complete head lathe mechanism. Automatic speed orchestra will be interspersed with change lever from 78 to 33 -1/3 rpm. Machined and balanced aluminum turn- shots of various sections or soloists. table, cast aluminum frame. Heavy duty Here demands that the precision- balanced motor. Overhead the picture feed mechanism incorporates a safety balance of the accompanying sound cutting head feature which lifts cutter from record as center of record is shall be altered so as to bring the anproached, thus preventing double cut- featured instrument or instruments ting and damage to stylii. Wide range. distortion -free amplifier. built -in volume into prominence, an alteration which level meter. High fidelity 8 -inch speaker. Transcription arm plays back discs may or may not be musically accept- up to 16" size. Inputs for high imped- able, according to the care taken by nce microphone. phono and radio. For 115 volts 60 cycles AC. Well -made the producer to fit his varying view- luggage -type carrying case is finished points to the music. Once again skill in attractive grey leatherette. Size is 25 x 22 x 12 inches. and musical knowledge arc required Price 329,95 in order to achieve a reasonable compromise. Advanced Model 180 As regards the control of level, WEBSTER - CHICAGO much wider variations are to be ex- Portable Wire Recorder pected in television than are normal with Exclusive in sound broadcasting. A concrete Record -O -Magic Controls example may make the reason for BROOK Model 12A3 HIGH this clear. Figure 6 illustrates a typ- QUALITY AUDIO AMPLIFIER ical arrangement for televising a dance band, where Cameras 1 and 2 are used for long and medium shots of the band and Camera 3 deals with solo items and announcements. The band will be picked up on Mic. 1 either slung or on boom, while announcements will be taken on Mic. 2 on a stand. The conductor normally occupies Position A. but at the end of a "number" will move to Within the range of its 10 waft The new Webster- t'hiea go "Electronic next to Stops Position B and announce the power rating, Model 12A3 is equal Memory" is easy use Automatic shut off motor before wire can run off item. He will be much further from in all respects fo the famous Brook either spool in either direction. Resets the microphone than he would be in 30 -watt amplifiers. automatically when Lock -fast Operating Lever is returned to center position. Push - a sound studio, but will probably not Along with virtually distortionless re- pull output Expanded Range amplifier speak any more loudly, so the output production. Model 12A3 features a allows recording of voice and music with measure of operating flexibility and excellent fidelity. Built -in Elapsed Time level will be very low. His announce- convenience which is unique in the Indicator permits accurate timing, cueing instantaneous- field of high -precision amplifiera. Al- and editing. New, powerful erase circuit. ment will be followed though designed primarily for home Removable Take -up Drum permits fast re- ly by the first chord of the new num- use as the heart of custom -built radio - load of recordings longer than one hour. phonographs, Its incomparable audio Has radio input and external speaker er ber, and unless the output of Mie. 2 characteristics make it equally suit- amplifier outlets. Compact luggage ease is cut very rapidly, the level will be able for laboratory or commercial measures 17 3/8" x 11 3/8" x 7 1 /2 ". Car- application where exacting engineer- rying weight is 27 lbs. Operates on 105- sufficient to cause severe over -modu- ing standards prevail. 120 volts. 50 or 60 cycles AC. Complete lation, and an unpleasant burst of with microphone, 3 spools of recording wire Complete with separate pre- ampli- and instructions. 149.50 sound. Price //e77 77VV fier and control Many useful accessories available to en- Thus it will be seen that both mi- cabinet 169.50 hance versatility -write for complete cala- crophone balance and level control log! are greatly affected by the require- WRITE FOR YOUR COPY OF OUR NEW 1949 ments of vision, and whereas in FREE! CATALOG OF HIGH QUALITY SOUND EQUIPMENT sound broadcasting, balance may fre- quently be left set for a complete programme, and slight control exercised on the output level, in television the continually changing conditions in the studio require constant alterations in the settings of Distributors of Radio & Electronic Equipment the various controls. YORK 7, N.Y. Phone -Worth 4.3311 Cable- TERMRADIO The question of the ratio between as CORTLAND,' ST. -NEW speech and accompanying music is

AUDIO ENGINEERING MARCH, 1949 41 probably as difficult to decide in tele- accompanying sound will probably in a noisy restaurant, with first one vision as it is in sound broadcasting. be excused or pass unnoticed. and then both ears will confirm this Tn general, the producer, who not The Future; Binaural Reproduction statement. Thus, in monaural repro- only knows the play or program but duction Mention has already been made in the salient features of the has the script in front of him as musical scene previous sections of various ways in must be exaggerated well, will demand a higher level of which the present techniques might and brouglzt into relief by manipula- music than the viewer, trying to un- be improved. The development tion of the balance. This will result, derstand the dialogue at first hear- of methods of providing variable acous- in general, in the use of microphone ing, would desire. The addition of tic conditions in the studio, positions nearer to the soloist than the picture, particularly if lip move- the design of a microphone with charac- the direct listener using both his ears ments are visible, will probably help would chose. In the same way, back- to decrease teristics more suited to the special the apparent masking ef- requirements ground noise of any sort is far more fect of the music. of television and the introduction of the technique of pre- noticeable in mònaural reproducing systems than is in real life. Remote Pickups recording have all been suggested as it It has already The problems faced by the sound desirable future achievements. Even been pointed out that the engineer during Remote Pick -ups if all these could be accomplished, maintenance of the microphone suf- ficiently will often be greater than those con- however, many of the problems of close to the sound source, fronting his studio counterparts. His television sound would still remain. and the reduction of studio noise, are arrangements for suspending or sup- In my opinion, the solution or ameli- both very real problems in tele- porting microphones will be cruder oration of most of the remaining vision, and it would seem that the and his acoustic conditions will vary difficulties lies in the development adoption of a binaural system would go a long way towards over even wider limits. Only in the and introduction of some form of solving both. case of the running commentary binaural reproduction. It must be Two distinct methods of binaural from an invisible commentator will remembered that even the most per- reproduction are possible. The first his task be relatively easy. Relays fect s i n g l e channel reproduction employs two microphones mounted from theaters will make the same bears to the original sound somewhat on either side of a block of wood of stringent demands from microphones the same relationship as does an ex- similar size to the human head. The as they do in sound broadcasting, al- cellent color photograph to the scene outputs of these are taken through though here again the picture may it portrays. The ears have to a large completely se p a rat e transmission help to clarify some point which extent lost the power of concentra- chains to two earphones worn by the sound alone would miss. But in gen- ting on any particular source of listener. The second method i n- eral, remote pick -ups will be chosen sound to the exclusion of all else. creases the spacing of the two mi- for pictorial ii.terest to such an ex- The simple experiment of listening crophones to several feet and repro- tent that tcclii.ical deficiencies in the to conversation from across the table duces the sound from two loud- It's Tops!

Surveys show that AUDIO ENGINEERING is preferred over all other technical magazines read by the best informed in the sound field -the broadcast engineers. Each issue brings you outstanding articles on five or more of the following subjects:

Broadcasting Public Address Sound on Film Industrial Sound equipment Recording and applications. Acoustic treatment of studios, Phono Reproduction rooms, auditoriums etc. In addition, each month Audio Engineering presents latest improvements in sound reproducing equipment design, test methods, and technical news from here and abroad. The editorial staff includes top authorities in the sound field. Subscribe NOW! Don't miss an issue! Please write for deter "_. of our special group rate covering 6 or more Subscriptions.

AUDIO ENGINEERING RADIO MAGAZINES, INC. 342 Madison Avenue, New York 17, N. Y.

Sirs: Here is my check (or money order) for $ Enter my subscription order to AUDIO ENGINEERING for the next issues. Subscription Price: In U.S.A., Canada and Pan America -12 issues $3 -24 issues $5. All others $1.00 more per year. Please check one: New Subscription Renewal

Name (please print)

Address City State Occupation (give title and department(..._...._...... _ Firm Name ...... _......

42 AUDIO ENGINEERING MARCH, 1949 speakers preferably spaced the same distance a p a r t. The headphones method gives a more perfect illusion, though it suffers from the psycho- logical disadvantage that when the listener turns his head the whole acoustic scene moves round with him. In watching a television program, however, it is probable that viewers will tend to keep their heads reasonably still. The reversion to headphone listening would doubtless be considered a retrograde step in many quarters, and experiments would be needed to In outward appearance determine how effective the loud- there is little difference be speaker method could be made, using tween a horn or loud speaker a spacing which could reasonably be of conventional type and its achieved in the modern home. It is counterpart in a Racon model. surprising how little work has been But under the surface there done so far on the whole subject of are many subtle differences t, binaural reproduction. Several iso- and improvements. lated trials have been carried out It is these invisible features and written up, as for example, the -the product of Racon ADVANCED relaying of a concert by the Phila- ENGINEERING-that give Racon units delphia Symphony Orchestra from their outstanding superiority in volume, Philadelphia to Washington, using range, clarity and freedom from reson- three wideband channels but no other ant effects. systematic investigation of the prob- (Top)- Permanent Magnet Horn Units lem, appears to have been under- These units, popular for all types of service, embody improvements developed during the taken. war. Higher power handling capacity and The most usual argument ad- greater efficiency. Designed for practically lifetime service. Two groups: one with Alnico vanced against the use of binaural V Magnets, one with Alnico Blue Dot Magnets. All steel reproduction is that it is uneconom- parts plated to prevent corro- ical to double the bandwidth occu- sion. Corrosion -proof metal or plastic diaphragms. With 'heavy pied by one program. This argument aluminum watertight case at $2.60 extra. Type illustrated is is, of course, of much less weight at Junior Giant with Alnico V the frequencies at which television Magnet, watertight case. Op- erates at 30 watts. transmission takes place. Several List Price $50.00. methods of providing the two channels present themselves. Two separate transmitters, above and below the vision signal in frequency, could be used, giving the possibility of pro- (Center)- Double Re- ducing simple receivers in which Entrant Marine Speakers -For l o n g only ,one sound channel is provided. range reproduction a n d Another method would be to use a pick -up, all types of service- Marine. Railroad and single pulse transmitter, with the Public Addresses. Waterproof ; im- two channels modulating alternate mune to extreme temperatures. Hea- vy aluminum spinning with heavy pulses. Here again, a simple single aluminum casting for base. Four models: Miniature Marine, bell diam. channel receiver could probably be both 6,Y.., ": Midget Marine, two sizes, produced which would give merely a 91/2" bell diam.: Regular Marine, bell diam. 14 ". Approved by Bureau of mixture of the two. Marine Inspection and Dept. of Com- would merce. Type shown. Regular Marine. In short then, it seem that hen diam. 14 ". List Price..$130.00. whereas from the general point of (Lower)- Double Re- Entrant Trumpet -Delivers view, a program of research into the highly concentrated sound over long distances with highest efficiency. Free from resonant effects. Base and whole question of binaural transmis- inside tone arm aluminum castings: bell heavy gauge aluminum spinning. Seven me:dels, hell diameters 101/4,, sion is overdue, the results of such 36 to 251/2 "; also four radial models in widths 9" to ". an investigation might find their Type shown, RE -35, hell diam. 19 ". List Price. $32.50. most beneficial use in helping to DON'T BE SATISFIED WITH "ORDINARY PERFORMANCE". solve some of the problems of tele- GET A RACON AND YOU GET THE BEST! vision sound. If. rite today /or new catalog of complete lire RACON ELECTRIC CO., INC. Conclusion 52 E. 19th St-eet., New York 3, N. Y. It is hoped that sufficient has been said to make it clear that, although n somewhat naturally the problems of Speakers vision technique have occupied the Horn Units forefront of interest and discussion Horns

AUDIO ENGINEERING MARCH, 1949 43 among television engineers, the pro- America's Announcing the Panoramic leading vision and maintenance of a high quality sound accompaniment to the Ultrasonic Analyzer Model SB -7 engineers picture is by no means a simple for easy, fast ultrasonic analysis of important/ straightforward task. Much still re- An entirely new instrument, the SB -7 is en- industrial mains to be done in the way of re- gineered to meet the urgent demands for search, development and training. panoramic reception of ultrasonics for ... organizations This article has attempted to indi- Carrier system monitoring Feedback system studies cate some of the fields in which work Harmonic analysis may be particularly needed. Transmission line investigation SWITCH Refer Telemetering to/ 1. D. C. Birkinshaw and D. R. Camp- High frequency vibration bell - "Studio Technique im Televi- analysis sion" - J.I.E.E., Part III, Sept. 1945. The SB -7, an automatic scanning receiver, 2. Townsend - "Contemporary Problems graphically presents frequency and level NEWARK in Television Sound" - Proc. I.R.E., of ultrasonic signals. Special control Jan. 1943. features enable selection and spreading for 3. Il. H. Bolt - "Studio Acoustics" - out of any narrow band ofr highly de- TV, Radio, Sound and Radio News, Jan. 1946. tailed examination. 4. W. A. Pozner - "Synchronization Tech- Recording Equipment, FEATURES nique" - J.S.M.P.E., Sept. 1946, Page Direct 197. readin" Replacement Parts and Linear frequency scale Electronic Tubes Continuously variable scan- Experimental Ultrasonics ning width because... Linear and 40 db linear log (from page .:31 amplitude scale NEWARK has the most complete on-the- Continuously adjustable spot stock of all standard equipment... about 20 cycles to over S kc, but with selectivity from the tiniest replacement port to the any pressure it will not be possible Stabilized frequency most complete installation ... on hand in 3 to prevent the jet of air from forcing calibrations giant centrally located stores, and tre- its way between fingers Wide input voltage range mendous warehousesl the and caus- ing oscillations. Write Dept. HR for complete NEWARK equipment is tops in quality, de- specifications pendability, and performance. Everything Now look at the scope and, if some On display at the March I.R.E. is Newark -tested and Newark- backed, so high frequency sine waves appear ou Convention, Booth 241 -2. you know it's the best! the screen, do not assume the jet is NEWARK delivers the goods...but fast) PANORAMIC RADIO CORP. oscillating; the white noise is merely 10 South Second Ave. Mt. Vernon, N. Y. 24 -Hour mail -order service...faster on exciting the crystal at some mode of phone or telegraph orders. oscillation. NEWARK offers the most complete essential reference book...148 illustrated pages Next, assemble. the generator and TV REAR PROJECTION? full of dota on over 20,000 standard brand set the cavity at about one diameter ... As Always S.O.S. Leads the Way items, including deep. If the cavity is .062, this will GET "HOLLYWOOD" EFFECTS, Standard and L -P pickups and changers be approximately 24 kc. Jam it light- MOVING BACKGROUNDS, Wire, tape and disc recorders Hi-Fi sound ly up against the jet and retract it 1 NO PAINTED BACKDROPS NO SPECIAL and P.A. equipment Speakers Mikes slowly. About one from SETS. Accessories etc. jet diameter S.O.S. the jet an oscillation will appear. Pull "Know How" it out another diameter and another Pays Off oscillation. somewhat weaker. will oc- - ¡ Also a Complete cur. Go back to the first position and V line of Studio. Re- cording and Labora- Send lock the cavity in position as closely TODAY tory Equipment. as possible to the optimum oscilla- For details and for FREE catalog ?trite new 1949 tion point. The cavity -depth adjustment screw S.O.S. CINEMA NEWARK can now be adjusted and SUPPLY CORP. the air pressure Dept. G, 602 W. 52nd St., New York 19 CATALOG varied slightly to obtain vernier action on the frequency and wave form. Have the AUDIO ENGINEERING SCHOOL genera- A practical Audio Engineering course in tor about 2 inches or so directly over Sound Fundamentals: FILM and MAGNET- IC Recording; Transmission Measurements: Also featuring a complete line of the pickup crystal. A whole variety Monitoring and Mining. Laboratories contain. RADIO AND TELEVISION KITS, SETS, of wave forms will be noticed. Transmission Sets, Oscillators, Distortion Sets; PARTS and ACCESSORIES for homes, Harmonic Analyzer; Intermodulation When the regulator is wide open, Analyzer and other enrol. Recording Studio hams and hobbyists) or the generator operating directly assimilating Broadcast, Motion Picture and 24 -HOUR MAIL -ORDER SERVICE Commercial Sound Recording. H. M. TRE- off the compressor. the variation in MAINE, Pres -Dir. 3 GREAT STORES! uptown atl lS W. 45th St. pressure due to the single cylinder Approved for Veterans and Foreign Visas Downtown at 212 Fulton St. in NEW YORK of. the comnressor will provide fre- HOLLYWOOD SOUND INSTITUTE Inc 323 W. Madison St. in the heart of CHICAGO -A quenev- mnrlulatpd signals that will 1040 No. Kenmore Hollywood 27. Calif. MAIL NOW! he quite fuzzy on the oscilloscope. IMEWARK After hemming familiar with the 2nd ANNUAL PENNY SALE! RADIO s rftIYISION . Dept. C21 frequency range of the generator. set For 1t' mere, you get 2. For Example: HI FIDELITY 20,000 ohms to 600 it at some mid -frequency ohms 2 "d a S3/_. NEWARK ELEC. point and "h Raytheon No. CRP 303 /SA. CO.. 242 W. 55th St., N. Y. C. Suitable from preamp. plate to line or phones. Please FREE slip on the send 1949 Newark Catalog to, parabolic reflector. It Flat from 15 to 20,000 (:PS. No. TX240 Ship. wt. I Name.. should focus to n circle lees than three 234 Ib.. $2.29 -2 for 52.30. Send for complete PENNY S I LE LISTINGS. Prires Address- inches in diameter at R feet. and the net f.o.b. our plant. Include postage & insurance. field strength should he about the UNIVERSAL GENERAL CORP. City State 365 Canal St., N. Y. 13 (Dept. A) WAlker 5 -9642 same as. the generato- 2 inches from

44 AUDIO ENGINEERING MARCH, 1949 the crystal, but without the reflector. The average generator will focus somewhat differently for maximum white noise and maximum sine wave. This is because the white noise field pattern is usually at dead right angles to the jet, but the sine wave is about 5 degrees away from the jet. Both their half -power points are about 15 to 20 degrees on a polar diagram. This means the center of the parabolic reflector is of no use. Another advantage of using the parabola is that close to the jet there AMERICAN AIRLINES CHOOSES is quite a current of air from the jet, but about ten feet away along ALTEC LANSING 8" SPEAKERS the beam this is negligible. You will find that you can make a FOR FAMOUS FLEET OF DC -6s shot from a wall or good reflection After exhaustive competitive in -flight a sheet of aluminum, for instance. , operating tests of Altec Lansing and The loss is undetectable. At 25 kc other speakers, American Airlines' four layers of a handkerchief will communications division engineers re- lower the signal about 30 db, and at ported: "Observers all voted for the 50 kc only one layer will do the same. Altec system on the basis of quality and clearness." Entire passenger fleet Technique of DC -6's will be Altec Lansing 8" This power is insufficient to do a 400B Dia -cone equipped. good job on smoke precipitation, 400B DIA-CONE SPECIFICATIONS: Send for brochure describing entire in a large glass 12 watts but by putting some Power Rating , :liter Lansing line of speakers, con - jar with a wide-open top, and sus- Voice Coil Impedance 8 ohms taining, frequency response curres. pending the reflector over it some Required Amplifier Output Impedance 4.8 ohms work can be done. With a one -lip com- 161 Sixth Avenue Voice Coil Diameter 11/4' New York 13. N.Y. clear in a pressor, the smoke should Speaker Diameter 81/4" LTEC 1161 North Vine St. very few seconds. Speaker Depth 3W Hollywood 38, Cal. In working with insects and births Weight 4 lbs. you usually focus down and place a large barrier in the path of the beam, with a hole accurately cut to size to pass just the beam, which can then be considered of uniform energy for a foot or so. To weaken the signal, do not cut the power on the jet but put an attenuator, such as one or several layers of cloth, in the beam. The writer has always had a wish to try one experiment in particular. Since our furred, feathered and in- sect friends usually respond to quite Booth . I. R. E. Show high frequencies, will someone direct x some high -power 20 -kc output down a complicated series of sat holes, such as exist in so many barns? It Transcription might be well to have some suitable dogs at the far end, and let me know Sound Effects how the party comes out? Warning-since many generators Lp e go as low in frequency as that of many experimenters' hearing range, Broadcasting Equipment try to avoid working for more than a few minutes at a time at, say, 14 kc. The annoyance is cumulative, and at this power nausea and headache can result without warning. It is also a good idea to have a "backboard" of a blanket or the like on which to focus the energy, as otherwise it will reflect endlessly and go around many corners, and may cause distress to a dog or canary at some distance. Dogs THE GRAY RESEARCH & DEVELOPMENT COMPANY, Inc. are affected above 26 kc, but seldom 16 ARBOR STREET HARTFORD, CONN. a young canary can be distressed at 36 kc.

AUDIO ENGINEERING MARCH, 1949 45 45 RPM Records [punt page Gl for the The New Speed 216 640AA CONDENSER MICROPHONE The new speed of 45 rpm was nut Exhibiting Manufacturers adopted to complicate the commercial situation; was are HIGH GAIN - 34 db it picked after consid- showing this label on their erable testing, to permit of better letters, literature and advertis- RESPONSE - Down 1 db at 40 cps; down 0.5 db sound quality than could be achieved ing. The spot -light is on the at 20 kc at 335'a rpm. The engineering reason- NEW at the Radio Engineer- OUTPUT Z ing -250 ohms; no is best developed through a coming Show, come and see- - change in re- parison with a 7" 33Vá rpm LP. 11 sponse for loads we assume both have a maximum re- from 250 ohms to Audio Equipment cording diameter of 6% inches, and a SMALL SIZE - P/8" dia. x 10" Registration $3. non- members, long pitch of 240 lines per inch, we bud that at the outer groove 1,35 $1. to IRE members. LIGHT WEIGHT Only 12 ounces X has - times the linear groove velocity of POWER REQUIREMENTS - 70 ma at 11/4 v; 2.5 ma at the 7" LP. if we record for 5 minutes 135 v. we find that the LP will be recorded LONG BATTERY LIFE - Virtually in to 5%s inches diameter, and X is immune to in to 4Y8 inches. The groove velocity changes in bat- at the inside will be 22% higher in tery voltage; the case of X. change of A vol- If the LP recordings tage from 1.4 to were made at a finer pitch, the advan- 1.0 reduces gain 1 tage of X could be reduced. For a db; B voltage from 3- minute record, the advantage in RAM 135 to 105, 0.6 db. favor of X is 28%. Further out, the ENGINEERING III The greatly improved performance advantage will approach 35% as a SHOW EXHIBITOR inherent in this new instrument is limit. GRAND CENTRAL PALACE - made possible by our extensive ex- We find, then, that for equal pro- A N - perience in subminiature techniques HOTEL cessing COMMODORE care, the Victor record 'will MARCH 7 to 10 have u 22 to 35% greater frequency Audio Instrument Company range available. This assumes, cor- rectly, 1947 Broadway, New York 23, N. Y. that both manufacturers use recording equipment with wide-frequency range, and that the reproduc- NO OBSOLESCENCE ing stylus tip is the bottleneck. The ONE AMPLIFIER for ALL RECORDS increase in available frequency PRECISE AUDIO range is interesting, but nowhere near . . . plus *Dynamic Noise Suppression as significant as the decrease in dis- MEASUREMENTS tortion. We may expect processing to Pickering and Company, Inc., leaders in cause some increase in distortion, the audio field, make available to the and "tracing distortion" at high lev- industry their specialized facilities for els will be of importance. Both these audio measurements. We are prepared to make factors are reduced by guaranteed an increase in measurements on any type of audio linear groove speed, and the reduc- equipment for manufacturers, dealers, or tion in distortion will be proportional consumers. to the square or cube of the increase in groove velocity. PICKERINÇ & CO. Inc. This means that Oceanside, N. Y. New developments in recording, regardless the amount of distortion in the repro- of turntable speed or pick -up point, will not obsolete the H. H. Scott type 210A amplifier duction of X will be 40 to 55% of because it already includes every feature that incurred in reproducing necessary for faithful reproduction of re- LP, at corded or broadcast music. the same diameter, if both processing And in addition, the built -in *Dynamic plants VERTICAL LATERAL Noise Suppressor assures freedom from are equally careful (or care- rumble, hiss, and the scratch that inevit- less). It is believed that the improve- REPRODUCERS RECONDITIONED ably increases with each playing of any types 9 -A, 9-B. D- 93306, MI -4886, 10.4E76 -O record. ment in fidelity was the factor which Complete Stock of New Replacement Parts Brilliant, realistic reproduction of every led Victor to retain the higher speed, for All Types record, 33. 45, or 78 RPM ... and of FM in spite This service is being used by leading radio and AM broadcasts as well ... is certain of the sales advantage of stations and wired music companies from now and for many years to come with the 33% rpm, coast to coast. Factory prices prevail. H. H. Scott 210A amplifier, Hear it TODAY and you'll agree that it VIBRATION SYSTEMS, INC. satisfies tomorrow's requirements. For com- Comparison of LP and X 1040 W. Fort St. Detroit 26. Michigan plete technical write data. Dept. 903AE2. A most thankless task is that of GUARANTEED FOR A FULL YEAR making an Licensed under U.S. and foreign patents engineering comparison pending and issued. of the two seven -inch designs. N 8 WIRE SHIELDED CABLE . Two No. 16, Six No. 20 tinned, stranded, matter what we say, both sides will copper, rubber insulated, coded lads. Water. complain vigorously about the auth- proof rubber jacket. Tinned copper armor NOS= S C OT T. INC. or's ,hield overall. New material -No. AE8. astigmatism. Lengths to 400 ft. Price 10e /ft., 990 /Mit., The comparison is valid only if we 6700 /101 ft. FOB Chicago warehouse. Trans -World Radio -Television Corp. "PA CA'A6F0 study lNGINFlRING- nominally similar discs, that is, 5639 Aberdeen St. Chicago 21. 111. 385 PUTNAM AVE. CAMBRIDGE 39, MASS, seven -inch against seven -inch. Some of Phones: Ustin 7 -4588 ENglewood 44454

46 AUDIO ENGINEERING MARCH, 1949 the unwary have compared seven -inch MODEL 1360 JACK MOUNTING PANEL It C A with twelve -inch Columbia. This is incorrect, for they fall in entirely different price classes, fit different markets, and cannot fairly be compared. It should also be pointed out that almost no ten- or twelve -inch LP records have been recorded to five- inch diameter. Most of those seen by the writer stop at six or seven inches. At the risk of being classed as a hopeless cynic, we are inclined to look on Columbia's seven -inch LP as an RCA X with most of the original Requires Only 1314" of Panel Space! features removed to make it easier to market. This is not meant to be PANEL is the only double row jack critical, for the present slump in the The Type 1360 JACK MOUNTING a rack multiple high). phonograph record field makes ex- panel made to fit the dimensions of standard (IN" pediency more significant that it All others require 21ií" of vertical panel space. usually is. Another feature is the use of a designation strip over each row of the 24 jacks. Processing is constructed of heavy durai, precision drilled and machined is to get acceptable pro- The unit It easier to take standard jacks. It is finished in light grey or satin black as you cessing quality in X, but this is not require. Special finishes are optional and may be obtained for a slight a guaranty. Processing quality in extra cost. America has always been erratic, and $12.75 F.O.B. Burbank, Cal. poor processing can ruin a record in NET PRICE (less jacks) design spite of the original engineer- Type 1399 -B Jacks (with normal "Make" contacts) $.77 each ing. In short, the contest between LP and X is a battle of processing departments as much as of recording CINEMA rooms. The low price of the seven - inch record will not permit scrapping ENGINEERING COMPANY many pressings, so quality control 1510 W. Verdugo Ave. Burbank, Calif. must anticipate rather than follow Cable Address: CINENG BURBANK production. In this respect particular - 1y the citation of factory experience with twelve -inch LP production is fallacious, for there is a 500% dif- CONTINUOUSLY ference in list price. A factory simply cannot pamper a ninety -cent record ID FCT,INCE VARIABLE as much as one selling at nearly five dollars. In all the argument three men have been pretty well ignored. It was Ampex Electric Corp., the rigorous mathematical study of manufacturer of the new tracing distortion by Pierce and Hunt, in 1938, which gave a firm Ampex broadcast -type foundation of fundamentals to ideas tape recorder,uses a of groove dimensional change. Rine Lenkurt Adjustable -Core Snepvangers played a significant part Molded Pot Assembly in the development of X just before for peaking the erasing the war. This was put on the shelf oscillator to required fre- when war conditions made vinylite in quency. Inductance is short supply. After the war, with the adjustable, stepless, in a he again brilliant Peter Goldmark, 20 p Cr cent range up to a played part in fine groove develop- 3 henries. ment. This time it was in the Colum- Other advantages arc bia research laboratory. Q, It was predicted that the author improved simplified would earn the obloquy of both sides shielding, economy of of the argument. Now for a sugges- space and weight, and the tion which will get the third side (the possibility of mounting public) angry too. Why not reduce Lenkurt knows how parts closer together. the radius of the standard 78 -rpm Write for data. record groove to '/a mil? This could be played interchangeably by a standard 3 mil needle, or by a 1 mil microgroove stylus. Under the latter con- LENKURT ELECTRIC CO. dition, the quality would be simply SAN CARLOS. CALIFORNIA superb.

AUDIO ENGINEERING MARCH, 1949 47 éYivu? 9.t AMPERITE ADVERTISING Studio Microphones INDEX at P.A. Prices

Ideal for e.- Altec Lansing Corp. 45 BROADCASTING Amperite Co., Inc. 48 RECORDING Arnold Engineering Co. 8 PUBLIC ADDRESS Audio Devices, Inc. Cover 2 "The ultimate in microphone quality," says Audio Instrument Co 46 Evan Rushing, sound engineer of the Hotel Brook Electronics, Inc. 48 New Yorker. ... THE NEW BROOK Shout right into the Camera Equipment Co. 36 10 WATT AMPLIFIER new Amperite Micro - phone-or stand feet Cannon Electric Dev, Co. 40 2 Yes, this is it -a genuine Brook High away - reproduction is Cinema Engineering Co. 47 Quality Amplifier in the moderate price always perfect. field, An amplifier of incomparable per- Not affected by Daven Company, The Cover 3 formance . equalling Brook 30 -watt any climatic conditions. models in all respects. RBLG -200 ohms Guaranteed to with- Electro Motive Mfg. Co., Inc. 2 Use of triodes in all stages-together stand severe "knocking RBHG -Hi -imp. with Brook-designed transformers, permits around." Electro- Voice, Inc. .29 cleanest amplification List ever achieved. Dis- $42.00 tortion is reduced to the vanishing point. Fairchild Recording "Kontak" Mikes No matter how discriminating you are, Equip. Corp. _ 35 this new Brook All- Triode Amplifier will Model SKH, list $12.00 surpass your most exacting expectations. Model KKH, list $18.00 Bear this finest of amplifiers at your Gray Research & Dev, Co. 45 dealer's NOW! Offer, Introductory Hartley, H. A. Co., Ltd. 48 Write TODAY For Free Copy of Technical Write for Special Bulletin and Detailed Distortion Analysis Special illustrated folder. and 4-page Hewlett- Packard Co. Offer: Hollywood Sound Institute 44 BROOK ELECTRONICS, Inc. AMPER /TE Gmpany Institute of Radio Engineers 46 Inc. Dept. AC -9, 34 DeHart Place 561 BROADWAY NEW YORK 12. N. Y. Jensen 5 Elizabeth 2, New Jersey Canada Ados Rodio Corp. Ltd., 560 King St. W., Toronto Manufacturing Co. LeBel, C. J. 32 Lenkurt Electric Co. 47 100 BETTER ELECTRONIC EQUIPMENT THE HARTLEY- TURNER Maurer, J. A. Inc. 33 Medical Electronics Co.. 38 STANDARDIZED MODEL 215 SPEAKER Newark Electric Co., Inc. 44 READY - The wide -spread response of American Panoramic Radio Corp. 44 music- lovers to our first advertisement Par -Metal Products Corp __48 TO has evoked some good- natured doubts -USE about our claim that the 215 Speaker Peerless Elec, Prods. 38 gives better reproduction than any other CABINETS at any price. "Have we," they ask, "for- Pickering & Co., Inc 46 saken the traditional British genius for Presto Recording Corp . 3I understatement so that our voice can be beard the better?" To that we answer. Professional Directory _... _ 32 "Emphatically No." rd2 CHASSIS We are convinced that high prices are Racon Electric Co., Inc. 43 e not necessary for high -fidelity -at any Radio Corp. of America ALL rate in the home. We believe that an PANELS engineer who really understands technol- (Broadcast Equip. Div.) P- A. ogy and music, and who is not content 16 -A, 16 -B, I6 -C, 16 -D to copy others, can produce a speaker of NEEDS superlative performance at a modest price. We believe it because thousands of British Scoff, H. H. Inc. 46 Par -Metal RACKS users say we have achieved it in the Hartley- Turner. Shallcross Manufacturing Co.._ 37 Equipment Shure Brothers, Inc. 6 is preferred by But to make the matter clearer We Service Men, have prepared a leaflet treating of this Somerset Laboratories, Inc. 39 in greater detail. A copy of this and our Amateurs, and catalog is yours free for the asking. Bet- S. O. S. Cinema Supply Corp. 44 Manufacturers ter still, send al today for "New Notes Sylvania Electric Products Inc. I because they're in Radio," an authoritative handbook on the whole subject of high -fidelity, and we adaptable, easy - will also keep you supplied with technical Terminal Radio Corp. ... _ 41 to- assemble, eco- data sheets all designed to help you nomical. Beautifully achieve new thrills and pleasures from Trans -World radio and records. Radio -Television Corp.. 46 designed, ruggedly \ constructed by spe. 't We shall be glad to co-operate with Turner Company, The 34 cialists. Famous for a limited number of dealers and custom -built manufacturers on an agency United Transformer Corp. quality and economy. basis. Write today for full details, Cover 4 Write for Catalog. stating the territory You cover. Universal General Corp. 44 H. PAR-META L A. HARTLEY Co., Ltd. U. S. Recording Co. _. 32 PRODUCTS 152, HAMMERSMITH Vibration Systems, Inc. 46 CORPORATION ROAD, 32 -62 -49th ST., LONG ISLAND CITY Wells, Winston 3, N. Y. LONDON, W. 6, ENGLAND 32 Export Dept.: Rocke International Corp. 13 East 40 Street, New York 16

48 AUDIO ENGINEERING MARCH, 1949 TWENTY YEARS OF ATTENUATOR PROGRESS

As one of the oldest and most progressive manufacturers of attenuators, we take pride in present- ing our recent contribution to the users of fine volume controls ... the "Knee -Action Switch.'" This revolutionary type of rotor is now being offered on Daven attenuators and switches at no additional cost. For longer life and uninterrupted performance, we offer a switch with the following advantages:

/ 011111 11/11141 wiping blades of the :Action Switch" I S5IIIDM DU1I11001 * Multiple "Knee- (OM are enclosed in a tamper -proof housing.

Each blade conductor is individually spring loaded, giv- 5111'11 SIIII(5 * 7 tn(IIl 1 11111(IION ing a perfect balance to the entire conducting surface. WV COMM 10101 511 111 10 511111 pressure on the contacts and slip rings is as- Uniform LOW LOS, MI(I111LIC * 7 111 INSULATION I* sured, resulting in low, even contact resistance, over MOIDIO Il1MIN11 10110 the life of a unit. 4t The considerably shorter rotor arms result in lower II SIIIN6 11n 1111(1(0 ron over -all switch resistance, due to the reduced conducting path. II 1051110 S'01 INDInWDIN1 * For specialized switch applications, where space is 01 5111(1 III I) OUNIlI6 5(1111 limited, this new type of switch construction permits up (I10OI III(N MONO PLAIT to 6 poles on a 23/4" diameter deck. A greater number 515 of poles may now be obtained than heretofore, on all smaller diameter units. .PATENTED For Further Inform ition Write to Dept. A-6

E 1 9 1 C E N T R A L A V E N U

N E W A R K 4 , N E W J E R S E Y ALLOY TRATRANSFORMERS designed speCtftc.Illy are nd small FOR HIPERM transformtransformers Weight o alloy °uaudio While light sacri- Hiperm fidelity has been The UTC act service. unit-, an d come ilit Y audio portable endab nor alloy for of the Hiperm units are simi't ensions, These in dimensions, characteristic Linear Stand- 20,0p0 cycles. famous freedficed. The from to to uniform and characteristics is design in general audio Series ardand

TC Hiperm Alloy Transformers Feature

True Hum Balancing Coil Structure m m FOR IMMEDIATE DELIVER From Your Distributor Balanced Variable Impedance Line Perm unit .. ro line reflections or transverse couplings.

. permits above chassis

mum shielding from induc -2 Multiple Coil, Semi -Toroidal Coil Structuré trY 54 m lop 2 3 s T coo 7 t 7 ,o F. nee. . t.. rREOUENCY IN CYCLES PER SECOND Transformers e of ` 1.5D8 Typical Curve for HA Series

Max Unbal. 1.,s, in Mok. DC Price primary 1 db Level $1q.00 from 5 MA Impedance 30_20,000 Impedance ohms in 24.00 Primary 60,000 250 200, Iwo sections YPe 50, 125, 22.00 T Application ohms 5 M o. mike, 333, D00 P. DB low hum picku .22 Low impedance Ala very 00 d to dicer 30 20,0 HA-1p0 pickup, s hiel internal ohms over- 27.00 line to grid' tri -alloy 50, 120,000 ns 2 oll, in two 1 9.00 os ohms SMA Some mike,tmike, up. IODX X331500200. bum pick ;22DB impedance line very to 0 LOpickup, multiple eld effect 30 -20,00 HA101 gr: 1s. shi 200. 250, 16.00 push -pull internal 50. 125. to with It's-alloy 250, ohmsohm 0 333, 500 22 DB os tow s Same ee ohm 10_20,000 HA -108 impeda 50, 1250200, 18.00 Mixing, ohms or multiple 135,000 MA HA108 mike, P'pickup ratio, 1 8,000 to 1.5:1 22 DB line. ohms each side 20.00 to Ppush. 15,0005,000 30_20.000 plate 200, 250, 5 MA Single 50,125, -32 DB HA-106 pull grids 500 ohms 30_20,000 8,000 to 333, 19.00 200, 250, 5 MA to multiple 15,000 °'t' S0, 125, DB 5;^gle plate ohms '; 32 to 300, 500 HA -113 5,000 30_20000 line. ohms 15, 10, B9's or 10,000 Pull 2.5, 1.2 Push line. to 7.5, 5, HA -134 2Á3's to 3,000 many to 5,000 ohms of the 2A3s o few otalo9. Push -pull only write for c HA-135 voice coil. listing includesavailable . . The above Transformers H ¡perm Alloy /f

13, N. Y ßN7, NEW PORN ARAB U CABLES N . YORK 16, STREET NEW 150 VARIC11 STREET, EAST 40th ,:. DIVISION .: %S: .: i EXPORT