THE SOUND ENGINEERING MAGAZINE April 1971 5, A Modular Console Design Studio Construction Techniques Low -Frequency Sound Absorbers Complete Guide to the West-Coast AES Convention U u1 www.americanradiohistory.com Turn on the Ampex AG-440B and listen: tape tension. Easy changeover from quarter - Perfect silence. inch to half -inch tape. The AG -4408 is also one the Switch to record: no pop. of most versatile recorders you can buy. Console. Portable. Or Hit the stop: no pop. rack installation. Start with one channel. Build up to four or more. It's Go from rewind to stop: no tape shrieking. the perfect reproducer for the future four channel stereo. The Ampex AG -440B is so mechanically quiet To hear other quiet reasons why the AG -440B some engineers use it in the same room with can be your best recorder /reproducer buy, and live microphones. It's so electronically quiet how you can put it to work for you for as little you can forget about switching pops. as $50 a month, give us a call. (415) 367 -4400. That's why, in its own quiet way, the AG -440B Or write Ampex Corporation, Professional Audio has become the standard of excellence. Division, M.S. 7 -13, Redwood City, Calif. 94063. Ampex quality is featured throughout: Rigid die - cast frame. Modular design with front -mounted circuit boards. Individual torque motors control AMPEX Ampex creates perfect silence. MEW The Ampex AG -4408 recorder /reproducer. See us at the A.E.S. Show, May 4 -7, Los Angeles Hilton (Booth 92 -96) (.i)rlr lll r)rr lir'urlrr 1r (:inrl www.americanradiohistory.com coming \oxt Month A most vital subject to audio pio- fessionals everywhere is the topic of a multi -part article beginning next month. THE SOUND ENGINEERING MAGAZINE The author is W. Dixon Ward of the University of Minnesota and his sub- ject is titled HEARING Loss AND AUDIO- APRIL 1970 Volume 4, Number 4 ENGINEERING. \Vedonot wish to frighten you, but you may just reflect a hit when you learn the relationship be- tween the volume levels sometimes found in monitoring rooms and irre- Table of Contents trievable hearing loss. This is must reading for all audio pros. Sidney Feldman himself an out- FEATURE ARTICLES standing recording engineer reports on Studio Construction Techniques a meeting which at the topic was William R. Graham 34 PHONOGRAPH RECORD COMPATIBILITY. Design He points out that a decade after the in- A Modular Console Edward J. Gately, Jr. 38 troduction of the stereo disc, the battle for compatibility still rages. Low-Frequency Sound Absorbers We will have a picture report on a Michael Rettinger 44 Disc RECORDING SEMINAR Gotham 38th AES Convention and Exhibition -Detail Map and List of Papers 48 Audio recently held in the lovely setting Primer on Methods and Scales of Noise Measurement, Part 4 (concluded) of Sterling Forest, N. V. Wayne Rudmose 54 And there will be our regular monthly columnists: George Alexandrovich, Nor- MONTHLY DEPARTMENTS man H. Crowhurst, Martin Dickstein, Letters 2 Arnold Schwartz, and John Woram. Coming in db, The Sound Engineering The Audio Engineer's Handbook 4 Magazine. George Alexandrovich The Feedback Loop Arnold Schwartz 10 The Sync Track John Woram 16 Theory and Practice Norman H. Crowhurst 20 Sound with Images Martin Dickstein 28 Aoout The db Bookcase 56 Classified 57 People, Places Happenings 5 the db is listed in Current Content.: Engineering and Techn, logy EDITORIAL BOARD OF REVIEW George Alexandrovich Sherman Fairchild Norman Anderson Prof. Latif Jiji ovcr Daniel R. von Recklinghausen William L. Robinson A fish -eye control room view at Paul Weathers John H. McConnell Audiotek Recording Studios. Minne- apolis, \linnesota. At the controls I)an db, the Sound Engineering Magazine is published monthly by Sagamore Publishing Company, Inc. Entire contents copyright ©1970 by Sagamore Publishing Co., Inc., 980 Old Country Road, Plainview, L.I., N.Y. 11803. Telephone Holmes, chief engineer. Audiotek uses (S16) 433 6530. db is published for those individuals and firms in professional audio -recording, broadcast, audio- such equipment as Scully, Dolby, CA, visual, sound reinforcement, consultants, video recording, film sound, etc Application should be made on the sub- scription form in the rear of each issue. Subscriptions are $6.00 per year ($7.00 per year outside U. S. Possessions. I.angevin. and I.ang, with a complement Canada, and Mexico) in U. S. funds. Single copies are 75c each Controlled Circulation postage paid at Easton, Pa. 18042. Editorial, Publishing, and Sales Offices: 980 Old Country Road, Plainview, New York 11803. Postmaster: of Neumann and Sony microphones. Form 3579 should be sent to above address. www.americanradiohistory.com noise measurements are meaningless: Robert Bach PUBLISHER I couldn't agree less! If phono preamps are designed to standards, then stand- Letters ard noise measurements made on them Larry Zide are conventional. EDITOR The Editor: We are soon to release a new preamp noise Mr. Smith's A Phono Reproduction with unweighted more than 80dB Bob Laurie Preamplifier (db Dec. 1969) deserves below program level, RIAA response ART DIRECTOR added comment. within 0.5dB and the below 0.035 per how The noise formula presented is valid cent. Anyone who knows can Marilyn Gold measure or compare. Mr. Smith's for noise voltage from a finite source - COPY EDITOR resistance and clearly indicates that article would have been immensely noise increases with source resistance. more valuable had he included industry - recognizable performance specifications. Richard L. Lerner It is quite misleading as presented, how- ASSISTANT EDITOR ever, since several very important fac- As it now stands, it appears more a promo for Ortofon and Spectra -Sonics tors are completely ignored. A. F. Gordon It implies that noise is zero if source than a serious professional presentation. CIRCULATION MANAGER resistance is zero -quite so if the ampli- If the product is good, then why not show how good? fier is noiseless. But real -life amplifiers Eloise Beach are not noiseless and system noise is ASST. CIRCULATION MGR. lowest when amplifier and source are Roger K. Odom optimized for the application. Mr. Engineering Mgr. Smith gives sole Spectra -Sonics Corp. credit to the low SALES OFFICES source resistance and fails to consider Ogden, Utah 84404 the intrinsic noise sources within the amplifier, such as 1/F or "flicker" New York 980 Old Country Road noise. Plainview, N.Y. 11803 Most cartridges are designed for high 516 -433-6530 impedance with good reason -high out- put voltage. Certainly, thermal noise Chicago increases by the square -root of resist- Mr. Smith responds: Jim Summers & Associates ance, but so does the voltage! What I would like to make the following 35 E. Wacker Drive better way to over -ride amplifier noise? Chicago, Ill. 60601 clarifications concerning my article in 312-263-1154 Amplifier input impedance is not a the December 1969 issue of db Maga- problem since it is usually necessary to zine. I believe my statement on page Denver add resistance to properly terminate the 25 concerning the 2 -ohm cartridge Roy McDonald Associates, Inc. cartridge. impedance and the 3 ohm amplifier 846 Lincoln Street Practical limits are determined by impedance was misleading. I had meant Denver, Colorado 80203 303-825-3325 cable lengths and the capacitive loading to say that the 2 -ohm cartridge im- of the source at high frequencies. Is pedance and the 3 -ohm output im- there real disadvantage in locating the pedance of the 104 preamplifier card Houston preamp within a few feet of the cart- Roy McDonald Associates, Inc. will permit long connecting lines with- 3130 Freeway is Southwest ridge? It interesting to note that out hum pickup and high frequency Houston, Texas 77006 Ortofon furnishes a step -up transformer attenuation. Actually, the 2 -ohm cart- 713-529-6711 with their cartridge. If the purpose of ridge impedance works into a 600 -ohm the article is to promote physical dis- input impedance on the 104 card. The Dallas tance between cartridge and preamp, signal voltage is developed across the Roy McDonald Associates Inc. then it should be so stated. 600 -ohm input impedance while the Semmons Tower West The noise formula defines thermal Suite 714 noise voltage is developed across the Dallas, Texas 75207 noise from a resistance, not an induct- 2 -ohm cartridge impedance. 414- 637 -4444 ance. How then, can we use the im- The noise formula presented is for pedance of the cartridge? It's the resist- noise voltage from a finite source re- ance of the source, not the impedance, San Francisco sistance. The Ortofon SL -15 cartridge Roy McDonald Associates, Inc. that determines the noise. If you rewind is of the moving -coil type and is resistive 625 Market Street the coil to he non -inductive, the im- in its impedance characteristic within San Francisco, California 94105 pedance will approach zero but the the audio spectrum. While it is true 415- 397 -5377 noise will remain the same- because that a transformer inside the cartridge the resistance is the same. will increase the cartridge output volt- Los Angeles Mr. Smith refers to "response -to age to improve the signal -to -noise per- Roy McDonald Associates Inc. 300 KHz." (without equalization) and formance of the preamplifier input 1313 West 8th Street "down below 10Hz." Honestly, now, Los Angeles, California 90018 stage, the detrimental effects on ambient 413 -483-1304 who can hear 300 KHz? What use is pickup, distortion, phase shift, and high unequalized response in a phono pre - frequency attenuation produced by the Portland amp? And what "program" material is transformer must be considered. The Roy McDonald Associates, Inc. down at 10Hz? RIAA Response is prime intent in the design of the pre- 2305 S.