Audio Power in Tbe Home

MARCH, 1957 50<t ENGINEERING MUSIC SOUND REPRODUCTION sc 9 | * , * oHOR VERo- : OUTPUT LOAD Performance of an output transformer at high and low frequencies may be checked by using L se those old iceboxes in your attic or basement to house a an oscilloscope in this manner. See page 21. complete system the vertical type makes a solid cabinet for equipment, while the chest type holds records. See page 24. ADEQUATE AUDIO POWER IN TBE HOME NEW CONCEPT OF STEREOPHONIC SOUND GET HOT MUSIC FROM A COOL CABINET "FREE-RIDING" CONTROL RELAYS www.americanradiohistory.com the new "Harkness," JBL Signature Model C40 is a lowboy console model backloaded folded horn designed to enclose either a 12" or 15" JBL Signature Extended Range Speaker or one of the Signature two unit, two-way speaker systems. Below a mechanical crossover point around 175 cps the rear of the speaker cone radiates into the throat of a six foot exponentially tapered horn. Above this point the front of the cone acts as a direct radiator. The carefully formulated taper rate, long horn path and large horn mouth, and solid JBL Signature monolithic construction aid'in the production of an added octave of clean, crisp bass. The enclosure with legs stands 233/4" high, is 377/8" wide, and 20" deep. "JBL" means JAMES B. LANSING SOUND, INC., 2439 fletcher drive, los angeles 39, California www.americanradiohistory.com what kind of MARCH, 1957 VOL. 41, No. 3 Successor to RADIO, Est. 1917. microphone do you need ? a hand-held microphone? Hia -Sfouijiie 535 ENGINEERING MUSIC SOUND REPRODUCTION C. G. McProud, Editor and Publisher Henry A. Schober, Business Manager Harrie K. Richardson, Associate Editor a iavalier Joan Dioguardi, Assistant Editor Janet M. Durgin, Production Manager microphone? Edgar E. Newman, Circulation Director Hia 535 Sanford L. Cahn, Advertising Director •MEMBER- Special Representative-— •MtlllUTi O* vtEO H. Thorpe Covington, 26 East Pearson Street, Chicago 11, III., a desk or 7 DEL 7-0506 -H0 floor stand c Mid West Representative— microphone? m ■ 1/ L ft Sanford R. Cowan, 300 W. 4Srd St., New Yorlc 36, N. Y. TVest Coast Representatives— liiA .Sfou(yne 535 James C. Galloway and J. W. Harbison, 6535 Wilshire Boulevard, Los Angeles 48, Calif. CONTENTS Audioclinic—Joseph Giovanelli Letters C dual-impedance New Literature 8 microphone? Coming Events 8 Editor's Report 12 Tke* 535 Hi-Fi in the Home—Musical Sound or Blast—Leonard Warren 15 Adequate Audio Power in the Home—James Moir 16 "Free-Riding" Control Relays—Ronald L. Ives 20 How an Output Transformer Causes Distortion—Part II—Norman II. a microphone 21 C rouch urst with on-off I Get Hot Musie From a Cool Cabinet—David K. Slifer 24 switch? A New Concept on the Physiological Aspect of Stereophonic Sound—Howard F. Hume 26 lb 535 Essentials of Combination Patents—Albert Woodruff Gray 30 Equipment Report—Capps CM-2000 Series Condenser Microphone and Power Supply—Audax Model KT "Do-it-yourself" Tone Arm 35 Record Revue—Edward Tatnall Canby 40 The Sfendyne "535" is an Audio ETC—Edivard Tatnall Canby 46 • The Slendyne omnidirectional dynamic can be trans- probe microphone with a Jazz and All That—Charles A. Robertson 50 ferred from one frequency range of 60 to About Music—Harold Lawrence 56 application to 1 3,000 cps. It is a rugged unit, designed New Products 58 another — in seconds — with- to provide fine-quality per- Industry Notes and People 71 formance for years—without out disconnect- deviation from its original Advertising Index . ... 72 ing the cable. critical standards. AUDIO (title registered U. S. Pat. Off.) is published monthly by Radio Magazines. Inc., Henry A. Schober, President; List Price $70.00 C. G. McProud, Secretary. Executive and Editorial Offices, 204 Front St., Mineola, N. Y. Subscription rates—U. S., Possessions, Canada and Mexico, $4.00 for one year, $7.00 for two years, all other countries. $5.00 per year Single copies 50*. Printed in U. S. A. at Lancaster. Pa. All rights reserved. Entire contents copyright 1957 by Radio Magazines, Inc. Entered aa Second Class Matter February 9, 1950 at the Post Office, Lancaster, Pa. under the Act of March 3, 1879. RADIO MAGAZINES, INC., P. O. Box 629, MINEOLA, N. Y. AUDIO MARCH, 1957 www.americanradiohistory.com AUDIOCLINIC ? ? JOSEPH GIOVANELLI* Plastic Resonance point where sound waves pass at the rate Q. What in meant by "plastic reso- of one foot per second, at a frequency of nance"? S. Kalmer, New York, N. Y. two cycles per second. This means that two A. Often, when the frequency response waves pass the observer during a single sec- of a pickup is measured, there is found to ond. Suppose the observer now proceeds at be a rise at a particular frequency. This a speed of one foot per second in the direc- may not be the fault of the pickup but may tion from whence the sound is coming. It be caused instead by a phenomenon known can now be easily seen that he will pass as plastic resonance, which operates in the twice as many waves as passed him before following manner. he was set in motion, doubling the fre- When the stylus moves in accordance quency to four cycles per second, raising with the modulation on the disc being the pitch of the tone one octave thereby. played, it strikes the groove walls, causing (Jonversely, if the observer moves in the them to give. However, they are flexible, same direction of travel as that of the and therefore spring back into place, push- sound waves, he will encounter fewer of ing the stylus in return. These effects are them per second, the exact number depend- not at all unlike those of a tuned circuit ing upon his velocity. It should be obvious (an inductance and capacitance connected that the same phenomenon would be noted in either parallel or series), whose resonant if the observer remained motionless and frequency is dependent in this case upon the sound source were in motion. It would the elasticity of the disc and the dynamic also occur if both the observer and the mass of the cartridge. All the mass of the source were moving, but at differing veloci- cartridge can be assumed to be at the ties. stylus tip, and is analogous to the induc- it should be said here that my figures tance or the circuit. If the resonance of were used only for illustration, so that the this circuit falls somewhere in the audio effects could be more dramatically evident. spectrum, some portion of tiie disc will The actual velocity of sound is approxi- correspond with resonance, causing exag mately IIUU feet per second in air, its exact gerated emphasis of a particular musical speed depending upon temperature and hu- tone. There are two ways ot eliminating midity. The velocity of sound waves is dif- this difficulty. One is introducing damping ferent when they travel in media other into the cartridge, which is tne same as than air. saying tliat a resistance has been placed across the tuned circuit, lowering its elli- ciency, tnougii not completely eliminating Transistor Gain its effectiveness. This has tne disadvantage, Q. How does one determine Die yain of however, of increasing the dynamic mass of a transistor? Edwin Fischer, Goldsboro, the pickup, and witn the high velocities N.C. encountered with present-day discs, groove A. Like a vacuum tube, the transistor damage is the prouable result, caused by has differing characteristics when operated the irresistable force striking a movable in the grounded, or common, base connec- object. Tne second method is to reduce the tion, common emitter connection, and com- dynamic mass of the cartridge to as low mon collector configuration. In all these a value as is practically possible. This re- connections, the gain is reckoned under sults in reducing the force with which the short-circuit conditions, meaning that no stylus strikes the groove wall, in turn caus- load is applied to the transistor, but rather, ing less displacement; since the mass is its output lead goes through an a.c. milli- NEW TRIAD smaller, the stylus may more quickly re- ammeter directly to its proper termination GENERAL CATALOG turn to its rest position. This results in an on the power supply. In all three instances, TR-57 increase of the resonant frequency, the the gain is measured by injecting a small amount of increase depending upon the re- a.c. signal into the input and measuring Lists the complete line of duction of the mass and upon the stiffness the resultant a.c. current in the output lead. transformers that have of any given disc. Obviously, records will The preceding discussion is illustrated at made .TRIAD "the symbol of last considerably longer under these condi- (A), (B), and (C) in Fig. 1, which repre- quality." Includes over 75 tions. sents the common base, common emitter, new items. Now available and common collector connections respec- from your distributor Doppler Effect tively. The gain under common base condi- or write .,. Q. What is meant by the Doppler effect' tions is represented by a. This forms the Norman Floyd, Puente, California basis for computing the gain under the re- A. How many times have we heard an maining two conditions. The a of a good airplane pass overhead, with the pitch of junction transistor should run between 0.95 the engines rising as the plane approaches,, and 1.00, though this latter figure is never only to fall sharply as it disappears in tha quite reached. If the a falls below 0.90, it distance.

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