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How to Make GOOD TAPE RECORDINGS Whether your budget is small or

by C. J. LEBEL large, whether you are a beginner Vice President, Audio Devices, Inc. or a devotee from way back, this This completely new handbook on tape recording, by one of the foremost authorities on the subject, contains up- complete and definitive guide can to-the-minute practical help for both the experienced tape recordist and the help you get the most enjoyment out novice. Written in concise nontechnical language, it can be read and easily understood by the most inexperienced. of your high-fidelity system.. At the same time, the professional will find a wealth of useful information which could be supplied only by a person of Mr. LeBel's knowledge and experience. All aspects of tape record- HIGH FIDELITY: A Practical Guide ing are covered. Cloth-bound Edition, $2.50 227 by CHARLES FOWLER Paper -bound Edition, $1.5o 229 As publisher of HIGH FIDELITY and AUDIOCRAFT Magazines, and author of many articles on high fidelity, there is little need to introduce Charles Fowler to readers of this magazine, nor to assure them of his ability to tell in clear, nontechnical language just how to evaluate, buy, and operate RECORD RATINGS - Compiled by Kurte hi-fi equipment for the optimum in lifelike reproduction. Myers, Chief, Music and Drama Department, Detroit Public Library. Edited by Richard S. Hill, Head, Reference Section, Music Division, Library of Congress. Gives clear, complete Here is the practical, expert advice needed by everyone who has, or expects to have, a high- This book is, without any question, the essen- information on: fidelity system. Starting with an introduction to tial reference for the discriminating buyer of sound, the author then describes the various links records. It indexes practically all serious music Loudspeakers, control units in the hi-fi system, explaining their features and ever recorded on LPs, listing the date and and preamplifiers, amplifiers, specifications so as to provide the most helpful issue of the most important American and speaker enclosures, pickups, criteria for evaluating, and for selecting and match- European periodicals in which reviews ap- record changers and turning components. 234 peared. Symbols indicate what the reviewer tables, tuners, room acoustics. 310 pages, 100 illustrations, $4.95 thought of that particular release. Full bib- liographical information is given for each record. $5.95. 224

Maintaining HI-FI EQUIPMENT - AUDIO HANDBOOKS by Norman H. Crowhurst - AMPLIFIERS, $1.00 213 PUBLIC by JOSEPH MARSHALL ADDRESS, $1.25 216 THE USE OF FEEDBACK, $1.00 214 A much needed book on the specialized approach necessary A.F. TRANSFORMERS, $1.00 215 QUEST FOR QUALITY, $1.50 217 to service high-fidelity equipment. The author discusses not only electronic faults, but the mechanical and acoustical defects Book Department which cause a hi-fi system to function less than perfectly. AUDIOCRAFT Magazine Hard cover, $ 5.00 232 Great Barrington, Mass. Soft cover, $2.90 233 I enclose $ for which please send me, postpaid, the books indicated by the circled numbers below. (No C.O.D.'s or charge orders, please.) Foreign orders sent at buyers' "For electronics technicians, repairmen, and audio enthusiasts risk. Add 55¢ for postage on foreign orders. Binder: $3.5o ea. 223 in general, this volume is a veritable audio bible ... (and) it 213 227 is truly up-to-date ... There is so much valuable practical in- NAME 214 229 215 formation in this well -indexed work that it should be at the 232 ADDRESS 216 finger tips of everyone who enjoys building or improving home 217 233 sound systems."-Richard D. Keller in AUDIOCRAFT Magazine. 223 234

DECEMBER 1956 I 6,ffid ffid erg* 2lZj Jensen TRIAXIAL e be ,9-ie beeider Six years ago Jensen introduced the TRIAXIAL which combined into one unitary assembly a special "woofer" and two horn -loaded compression -drive "tweeters" to span the audio frequency range with an entirely new smoothness and realism unmatched by any other loudspeaker for listening quality. It is a fact that only Jensen makes a unitary true three-way loudspeaker with three electrically and acoustically independent speaker systems. Today the TRIAXIAL is still the unchallenged peer of "all -in -one" loudspeakers. *TRIAXIAL is a registered trademark of Jensen Manufacturing Company

MANefenäen UFACTURING COMPANY Division of The Muter Company, 6601 So. Laramie Ave., Chicago 38,111, In Canada: Copper Wire Products Ltd., Licensee WORLD'S QUALITY STANDARD FOR MORE THAN A QUARTER CENTURY

2 AUDIOCRAFT MAGAZINE December 1956

Volume 1 Number 14

THE HOW -TO -DO - IT MAGAZINE OF HOME SOUND REPRODUCTION

John D. Seagrave, whose name appears The Grounded Ear, by Joseph Marshall in the list of AUDIOCRAFT authors for the first time this issue, is an experimental What's new and significant in sound reproduction nuclear physicist at the Los Alamos Scien- tific Laboratory. He is a graduate of Cal Audionews 6 Tech with a B.S. in Electrical Engineering and a Ph.D. in Physics. Among his spare - Tips for the Woodcrafter, by George Bowe . .... Io time activities are several forms of "recrea- This tional" physics; one of them resulted in his issue: Sharpening power tools. two-part article on pickup -arm tracking, which begins this month. Tape News and Views, by J. Gordon Holt 14 Although a newcomer to technical audio - This issue: Choosing the best tape for your recorder. craft, Dr. Seagrave is an amateur musician of distinction. He is both Director of Readers' Forum 15 Music for the United Church of Los Alamos and Director of the Los Alamos Editorial Choral Society. 15 In "Minimizing Pickup Tracking Error", Build an AM Crystal the nature of tracking distortion is dis- Tuner, by John J. Stern, M. D. i6 cussed and its dependence on pickup -arm Details on two AM diode -detector tuner circuits, with an design and mounting is developed quan- AUDIOCRAFT kit report on the Miller 565 kit. titatively. Practical graphs and formulas are given both for optimum design of arms Minimizing Pickup Tracking Error, by Dr. John D. Seagrave 19 and for placement of commercial arms to Part 1: Nature of the distortion; development of a distortion produce minimum distortion. index; the tracking equation; interpreting distortion index. The conclusions reached in this paper will cause some furor, because they are Recording at MIT not identical with those made in previous 22 studies of the subject. Dr. Seagrave has The fabulous acoustic properties of Kresge Auditorium and used more accurate simplifications in de- MIT Chapel are now being exploited for music recording. riving design formulas than were applied before, and he has assumed more realistic Loudspeakers and Enclosures, by George L. Augspurger ...... 24 groove diameter limits - particularly for Part 4: Horn drivers and enclosures. LP's. His article is a major addition to design literature. pickup -arm Transistors in Audio Circuits, by Paul Penfield, Jr. CHARLES FOWLER, Publisher Part 3a: Junction transistor characteristics. ROY F. ALLISON, Editor Sound Fanciers' Guide, D. FRANK R. WRIGHT, Managing Editor by R. Darrell 28 ELEANORE B. WRIGHT, Reviews of exceptional disc and tape records Editorial Assistant Book ROY LINDSTROM, Art Director Reviews, by Richard D. Keller 29 ELEANOR GILCHRIST, Art Assistant Audio Aids FRANCES A. NEWBURY, Manager, 3° Book Division Sound Sales Directory Contributing Editors 42 R. D. DARRELL J. GORDON HOLT Advertising Index JOSEPH MARSHALL 45 B. SYER, Business Manager WARREN Index to Volume I ARTHUR J. GRIFFIN, Circulation 46 Manager Article and author index for AUDIOCRAFT, Nov. 1955 through Dec. 1956. Advertising Main Office - Claire Eddings, The Publish- ing House, Great Barrington, Mass. Telephone: Audiurraft Magazine is published monthly by Audiocom, Inc., at Great Barrington, Mass. Telephone: Great Barrington 1300. Great Barrington 1300. Editorial, publication, and circulation offices at: The Publishing Eastern- Lee P. Adams, AUDIOCRAFT, 353 Barrington, Mass. Subscriptions: House, Great $4.00 per year in the United States and Canada. Single copies: Fourth Avenue, New York 10, N. Y. Telephone: 35 cents each. Editorial contributions will be welcomed by the editor. Payment for Murray Hill 5-5400. will be arranged prior to articles accepted publication. Unsolicited manuscripts should be accompanied by return Midwestern- John R. Rutherford & Associates, postage. Entered as second-class matter October 1, 1955, at the post office, Inc., 230 East Ohio St. Telephone: Great Barrington, Mass.. Whitehall under the act of March 3, 1879. Additional entry at the post office, Pittsfield, Mass. 4-6715. the U. S. A. by the Ben Franklin Printed in Press, Pittsfield, Mass. Copyright -1956 by Audiocom, Inc. The Western-Brand & Brand, Inc., 6314 San cover design and contents of Audiocraft Magazine are fully protected by copyrights Vicente Blvd. Telephone: Webster 8-3971. reproduced in any manner. and must not be

DECEMBER 1956 3 The

by Joseph Marshall

Tape Quality frequency response both in the tapes mean we should have trick demon- themselves and in playback equipment stration records with snatches of tri- J. In a recent issue of AUDIOCRAFT, will be solved to a degree which will angle, drums, and organ. I mean com- col- Gordon Holt devoted his monthly give listeners an opportunity to realize plete recordings of music worth hear- umn to answering the question, "Why the theoretical advantages of tape re- ing as music, in brilliant performances want aren't tape records better?" I don't cording, at a price comparable with and with brilliant sound quality. There to shoe -horn myself into his field, but that for disc equipment. But it does are hundreds of discs that may be used my own his remarks have stimulated explain why the market for tape repro- for such purposes. I presume that mas- reflections which have convinced me ducers and for recorded tape is -not ters of some are available for duplication that those interested in exploiting the bigger than it is. In the high-fidelity in tape. One reason high-fidelity disc possibilities of tape reproduction must field consumers have enough knowledge recording has found such a wide audi- give this question and its answers some and discrimination to recognize quality ence (and market) is that there is an serious consideration soon. when they hear it. They are not going abundance of spectacular recordings As for tape quality, I haven't heard to invest in tape reproducers or tapes which show off the superiority of high any large percentage of the available until they can hear superiority in tape fidelity most persuasively. The absence tapes. But I have heard a pretty repre- reproduction. of similar tape recordings is handicap- sentative cross section, and I would And that brings me to the point I ping the tape field by understating its generalize my own experience with them principally want to make here. There capabilities. As long as discs are judged in the flat statement that the best are few tapes worth listening to from by playing spectacular examples of discs, duplicated tapes available when played a strictly hi-fi point of view. I will go and tapes are judged by run-of-the-mill back on the best available tape repro- further and say there are few that do examples both of music and of sound ducers are no better than the best discs quality, the disc will seem even more reproduced on the bést disc equipment, superior than it is in fact. and the great majority are not as good. Furthermore, there is very little recorded Disc Recordings tape material. I'll probably seem inconsistent when I Mr. Holt has given some reasons for present some thoughts stimulated by the seeming paradox of tape quality, one of my readers, who commends me and particularly the limitations of the present standards of tape reproduction for my comments on overcut recordings. tape -duplicating processes. I might, as real justice. Several times I have asked He makes this observation: most re- a reminder, point out the even more tape producers to send me samples of cordings today are meant to reproduce basic fact that the best available tape their most spectacular tapes. They have the listening experience of the concert playback machines cannot cover the fre- complied generously, but in my entire hall, but are actually played back in the quency range at 71/2 ips that almost any library of tapes I can think of only home where the dynamic range of the good magnetic phono cartridge can at one or two which I could recommend concert hall is more a nuisance than a 33 rpm. The Concertone 20/20, for to a dealer for demonstration purposes. virtue. He puts his finger, of course, example, which represents an excep- Nobody seems to have given any on the paradox which faces the whole tional value at around $500, has a thought to the matter of producing field of musical reproduction. We want cutoff at around 15,000 cps . when in tapes spectacular enough to sell tape re- reproduction which duplicates as nearly peak operating condition. As for the production. Indeed, I have had to pro- as possible the original sound which machines in the $100 to $200 class, duce tapes of my own - dubbed from exists in the concert hall; but it is a their response is scarcely better than that various disc recordings - to use for patent impossibility to expect, in a of now -obsolete magnetic pickups and demonstration. Although these home- 3,000 -cubic foot living room, to dupli- the average ceramic hi-fi cartridges. Al- made tapes fall far short of demon- cate the acoustic conditions which exist though some listeners like the tapes strating the quality possible on tape in a 300,000 -cubic foot (or larger) better because, even with the narrower today, nevertheless they are better in auditorium. The task of the recording frequency range, they are less noisy and over-all impact on the listener. engineer is to try to work out a com- cleaner on most peaks, the fact is that It seems to me that if tape pro- promise which gives an acceptable illu- 71/2-ips tapes do not have any other ducers are serious about exploiting the sion; some of these attempts are better clear superiority for the hi-fi listener high-fidelity market for recorded tape, than others, but none solves the para- and do possess the disadvantages of the first thing they should do is put out dox and it is highly doubtful that any- greater expense and awkwardness in use some tapes good enough and spectacular one ever will. On the other hand, my and storage. enough to show off the capabilities of reader has a point when he complains This frank criticism is not meant to the medium. I am aware that several that recording engineers do not seem be an indictment. Tape reproduction manufacturers of tape reproducers have to be as aware of the limitations of the is still in its infancy, compared with demonstration tapes, but - without ex- home listening environment as they disc reproduction. I have no doubt that ception - those I have heard don't ought to be and that, in consequence, in a very short time the problems of serve their intended purpose. I don't some recordings, particularly those with

4 AUDIOCRAFT MAGAZINE a very wide dynamic range, are more painful than exciting when played back have fun ...save money in the average home. I will have to agree with that. I love recordings with a wide dynamic range when I'm in a high-fidelity mood. But I must concede that, when I'm trying to enjoy the music as music, the extreme dynamic range is often more distracting than helpful. One has two choices: either to set the volume controls so the peaks do not blast you out of the room - and stimulate the neighbors to call the cops - in which case the diminuendos and quiet passages disappear into the room background noise; or to adjust volume so that low and average levels are comfortable, at the risk of inviting the objection of wife, child, and neighbors to the blast of the peaks and crescendos. It is of no use for anyone to tell me that if I can't tolerate those peaks I don't really appreciate music as it should be played. I respond that The famous University CLASSIC speaker system (shown at nobody should pay for his love of music right), represents the highest achievement in audio engineering. the ultimate in sound! The CLASSIC is a true, folded, self- with the sacrifice of his own peace of contained exponential horn which operates the woofer as a compression driver for maximum efficiency. Each detail has been mind, let alone that of his family; no carefully worked out that the complete system functions as a further, I point out that the loudest beautifully coordinated team. A truly self-sufficient cabinet. it funetions independently of walls and floor, achieving an amazing peak in the auditorium is by no means -realism... almost like having a concert orchestra in your own home. The superb craftsmanship of the cabinet and high Univer- as shocking to the ear of the listener sity standards to which the CLASSIC components have been built in the auditorium as a 5 -watt peak make the price really attractive. Mahogany $450.00, Blond $460.00. may be in a living room. I don't know the answer for this paradox. Back in the old days of 78- BUILD ONE OF THE FINEST rpm shellacs the records were tailored for home reproduction. Although they SPEAKER SYSTEMS IN THE WORLD seldom annoyed the listener because of wide dynamics, they sound awfully flat University has taken the heart of the magnificent CLASSIC system and made it available as the EN-CB UNFINISHED -UTILITY today. And, for all its annoyance poten- enclosure. It came about as a result of an overwhelming demand tial, the wide dynamic range of today's on the part of "do-it-yourself" enthusiasts who wanted to build recordings has an undeniable brilliance their own CLASSIC system. The price of the EN -CB is only $120.00 and stimulation the old ones couldn't The EN -CB is a superb piece of craftsmanship-constructed BUILT- INS hint at. But my reader's complaint is of Grade 1 Birch plywood using locked and mitred joints and by no means an isolated one. If you braced with heavy glue blocks for maximum efficiency. Supplied will check your acquaintances, especially with full instructions to mount speakers and network compon- those who don't care about high-fidelity ents. Designed acoustically to permit versatile use as "lowboy" sound, you will find it echoed time and or "highboy." again. My reader appears to think that Naturally, all speakers sound better in an EN -CB. Recom- mended are CLASSIC components: C15W woofer, Cobreflex-2 we ought to have ROOM - DIVIDERS two parallel series mid -range horn with T-30 driver, HF -206 "Reciprocating -Flare" of records: those of wide dynamics for super-tweeter and N-3 ACOUSTIC BATON crossover network. the high-fidelity people, and those with the peaks compressed for people who The EN -CB is a boon to the home decorator who plans to cus- are willing to sacrifice dynamic range tom build part of his furniture. Decorating ideas are limitless: to avoid the distraction of blasting. I BUILT-INS-Easily installed into closet or wall, or into large wall- PICK A PERIOD rather doubt that this is feasible or ad- to-wall installations. visable. There is at present, among ROOM-DIVIDERS-Can be used vertically or horizontally. the different labels, a sufficient variety PICK A PERIOD-Any furniture period can be achieved by treat- of reproduction so that one can usually ment of front frame moulding, base, grille fabric, etc. be found to suit one category or the CUSTOM FINISHING-Can be stained and finished Blond, Mahog- other of listener. But I do think that any, etc. Surface treatments: enamel, leather, formica, etc. CUSTOM FINISHING there may be a tendency on the part THE COMPONENTS THAT MAKE THE CLASSIC THg ULTIMATE IN SOUND of recording engineers to overlook this angle. Possibly, it might be well for them to audition recordings in a reasonably representative or typical living room rather than in a studio or the concert hall itself and, without return- claw COBREFLEX2 T.30 N-3 ing to the extreme flatness of the old days, minimize those excursions in dynamic range which are not reasonably LISTEN tolerable in the home. In any event, Continued on page 37 UNIVERSITY LOUDSPEAKERS, INC., 80 SOUTH KENSICO AVENUE, WHITE PLAINS. N. Y.

DECEMBER 1956 5 ETCHED -CIRCUIT OSCILLOSCOPE microphones and electronic components, Shure Distributor or directly from the KIT have announced a new General Cata- manufacturer. The new Heathkit Model 0M-2 etched - logue No. 56 covering microphones, FM -ANTENNA BOOKLET circuit 5 -inch oscilloscope kit is reported microphone cartridges, microphone ac- to be an improvement over the pre- cessories, phono -pickup cartridges, and A booklet, All About FM Antennae magnetic and Their Installation, by L. F. B. ceding model by providing wider verti - recording heads. The technical data and general information in Carini, is being offered for sale by the the catalogue have been prepared with Apparatus Development Company of the customer in mind; questions have Wethersfield, Conn. been anticipated so that persons buying The booklet covers such subjects the products described will find the kind as "Why an FM Antenna?", "What of information they need to evaluate the Constitutes a Good FM Antenna", usefulness of a given model. "Choosing the Correct Antenna for your To those persons engaged in buying, Installation", "Antenna for Fringe Re- selling, and installing the products de - ception", and "Long Distance FM Re- ception". Also included is an FM station directory. The price of the booklet is 250.

PRECISION NEEDLE FILE KIT The Sal'>: A kit of precision needle files has been Voice and introduced by Centralab. Made in Swit- zerland, these high-grade carbon -steel files are 51/2 in. long. There are seven individual shapes: round, half-round, flat, square, oval, triangular, and knife edge. All have a No. 0 cutting surface. The files are packaged in a sturdy Latest Heathkit etched -circuit scope. cal frequency response, extended sweep - generator coverage, and increased stability. Vertical frequency response is said to be essentially flat to over 1 Mc, and down only 11/2 db at 500 Kc. The sweep -generator multivibrator functions New Shure catalogue, free on request. reliably from 30 to 200,000 cps, almost twice the coverage provided by the pre- scribed, Catalogue No. 56 will be a vious model, according to the manu- source of general and technical data that facturer. Deflection amplifiers are push- will help them in recommending a par- pull, and etched circuits are employed ticular model. The catalogue can be in critical parts of the design. A 5BP1 obtained free from any Authorized cathode-ray tube is used. The scope features external or in- For more information about any of ternal sweep and sync., one -volt peak - the products mentioned in Audio - to -peak reference voltage, 3 -position news, we suggest that you make use step -attenuated input, and adjustable of the Product Information Cards Centralab set of No. o needle files. spot -shape control. A calibrated grid bound in at the back of the maga- screen is also provided for the face of zine. Simply fill out the card, giving plastic tube, and are said to be a great the CRT, allowing more precise obser- the name of the product in which aid to servicemen, hams, and the do-it- vation of wave shapes displayed. you're interested, the manufacturer's yourself hobbyist. The new Model 0M-2 is designed name, and the page reference. Be JENSEN DO-IT-YOURSELF for general application wherever a sure to put down your name and DESIGNS reliable instrument with good response address too. Send the cards to us and characteristics may be required. Addi- we'll send them along to the manu- The Jensen Manufacturing Company tional information will be furnished on facturers. Use this service; save has recently published a booklet of do- request. postage and the trouble of making it-yourself designs for speaker systems. The booklet, Technical Manual 1060, SHURE GENERAL CATALOGUE individual inquiries to a number of different addresses. contains 18 simplified plans and com- Inc., Shure Brothers, manufacturers of plete instructions for building self -con -

6 AUDIOCRAFT MAGAZINE rained or built-in single speaker and excellent means of providing good cir- ment, and quick replacement of the car- 2- and 3 -way speaker systems. It in- cuit continuity when using components tridge can be accomplished without use cludes complete parts lists and speaker with adjustable or moving contact sur- of special tools. data for all types of enclosures men- faces. It is especially suitable for Other basic Climatite models, with tioned. making connections to tubes with co- their specifications as supplied by the Persons interested in constructing a axial terminals; or to moving parts, such manufacturer, are: speaker system will find the booklet The Model 310T: 3 volts output; com- a guide to the space, structural, compliance of 0.7 X 10-6 cm/dyne; fre- ponent, and assembly requirements of quency response from 5o to 12,000 cps. modern speaker systems. The reader is Turnover cartridge contains separate s- assisted in the choice of a speaker sys- and 3 -mil synthetic sapphire -tipped tem by discussion of the relative per- needles. formance of various combinations of The Model 312T: o.8 volts output; Jensen speakers and speaker -system kits compliance of 2 X ro -6 cm/dyne; fre- in the enclosures suggested. The booklet is available from local Jensen distributors or directly from the Jensen Manufacturing Company. Price is 50¢. WRIST -ACTION PICKUP ARM Eimac finger stock for sliding contacts. The Metzner Engineering Corporation of Hollywood, Calif., manufacturers of as long -line and cavity -type circuits; and the Starlight turntable, have announced it is also useful in acting as an electrical a new Starlight Transcription Arm fea- "weather-strip" around access doors to turing an exclusive "double -wrist ac- equipment cabinets. tion" head which is counterbalanced and Astatic ceramic phono pickup cartridges. has weight adjustment from 4 to 14 LAFAYETTE FM -AM TUNER KIT quency response from 3o to 15,000 grams. The retail price is under $25.00, Lafayette's new FM -AM tuner kit in- cps. less cartridge. corporates an Armstrong FM circuit Cartridge is turnover type, containing According to the manufacturer the with limiter and Foster -Seeley discrimi- separate r- and 3 -mil synthetic sapphire - tipped counterbalanced, double -wrist action nator. AFC can be disabled to allow needles. The Model 414-r for 45 rpm changers: head provides minimum mass and as- tuning weak stations. The front end same specifications as sures prefect tracking and reduced consists of a grounded -grid triode am- Model 3roT, but has single r -mil sapphire -tipped needle. record wear. Resonance is said to be plifier and separate mixer and oscillator. Climatite cartridges are delivered ready outside the audible range. The arm lifts The AM superheterodyne section fea - for direct miniature -cartridge replace- to a vertical position for cartridge re- ment, and they can be supplied with placement, is 12 in. long, and plays all brackets, spindles, and mountings for record sizes up to and including 16 -inch all original equipment applications. records. An illustrated brochure showing both MASCO FM -AM TUNER AND the Starlight turntable and the new AMPLIFIER transcription arm is available by writing Mark Simpson Manufacturing Co., Inc., has announced the Masco Music Master, Model AFR, a single -chassis FM -AM tuner and 10 -watt amplifier. Only a speaker and a record changer are required to complete a home music sys- Lafayette KT-roo FM -AM tuner kit. tem. The Music Master also incorporates a preamplifier; it is equalized tures AVC, a ferrite -core antenna, and for LP records, as well as 78's, and a high -impedance terminal for external has separate bass and treble controls. antenna. Tuning is flywheel counter- The FM section utilizes the Arm- The kit includes weighted. all parts and strong circuit, with limiter and Foster - easy -to -follow instructions. The Lafa- yette stock number is KT -100; the price is $32.50. CLIMATITE PHONO CARTRIDGE Metzner Starlight transcription arm. The Climatite series of phono cartridges to the Metzner Engineering Corpora- was announced recently by the Astatic tion, Department 29, 1041 North Syca- Corporation. The new series is designed more Ave., Hollywood 38, Calif. to meet all requirements of. the phonograph industry, and is said to be ideal Complete FM -AM receiver by Masco. EIMAC PREFORMED CONTACT for use in areas of extreme cold, heat, FINGER STOCK or humidity. Seeley discriminator. The superhetero- Eimac Preformed Contact Finger Stock Currently available is the Climatite dyne AM circuit has been designed for is a prepared strip of spring material Model 42ots, reported to be a high -out- sensitivity and selectivity. slotted and formed into a series of put, high -compliance, wide -range turn- The unit is rated at 10 watts audio fingers designed to make sliding con- over unit containing separate, removable, output, and is said to have a frequency tact. 1- and 3 -mil synthetic sapphire styli. range of 20 to 20,000 cps with less Eimac Finger Stock is said to be an Unique design simplifies stylus replace- than 1% distortion.

DECEMBER 1956 7 zwel-zegef ziovfr You can enjoy savings without sacrificing quality- if you "build -it -yourself" and eliminate labor charges; and if you buy direct from the manufacturer and eliminate extra profit.

Here's what you get: High-fidelity amplifiers, tuners, and speakers that you assemble yourself, from the step-by-step instructions furnished. You get, top-quality parts at lower cost through Heath mass purchasing power. You get the equivalent of systems costing approximately twice the Heathkit price.

MATCHING CABINETS The Heathkit AM tuner, FM tuner, and preamplifier kits may be stacked one on the other to form a compact "master control" for your hi -fl system.

BG -1

FM -3A

WA -P2

HERE'S WHY Aeathkit IS FUN TO BUILD: Instructions are complete, and our amazing step-by-step method, tied -in with large pictorial illústrations, guide the beginner through each stage of assembly. If you can follow directions you can succeed, and can build high-fidelity equipment you will be proud to show off to your family and friends.

Here's the proof: Thousands of Heathkits have been built at home by people just like yourself, and you should treat yourself to this same experience by dealing with the world's largest manufacturer of top-quality electronic kits for home and industry.

8 AUDIOCRAFT MAGAZINE Heathkit Model FM -3A High Fidelity FM Tuner Kit HEATHKIT SPEAKER SYSTEM KITS Features A.G.C., and stabilized, temperature -compensated oscillator. Ten uy sensitivity for 20 DB of quieting. Covers standard FM These speaker systems are a very vocal demonstration band from 88 to 108 mc. Ratio detector for efficient hi-fi $2695* of what can be done with high -quality speakers in en- performance. Power supply built in. Illuminated slide rule (With Cabinet) closures that are designed especially to receive them. dial. Pre -aligned coils and front end tuning unit. Shpg. Wt. 7 Lbs. Notice, too, that these two enclosures are designed to Heathkit Model BC -1 Broadband AM Tuner Kit work together, as your high-fidelity system expands. Special AM tuner circuit features broad band width, high Heathkit Model SS -1 High Fidelity sensitivity and good selectivity. Employs special detector $2695* Speaker System Kit for minimum signal distortion. Covers 550 to 1600 kc. RF (With Cabinet) Employing two Jensen speakers, and coils pre -aligned. supply is in. Shpg. Wt. 8 Lbs. IF Power built the Model SS -1 covers 50 to Heathkit Model WA -P2 High Fidelity Preamplifier Kit 12,000 CPS within t 5 DB. It Provides 5 inputs, each with individual level controls. Tone controls pro- can fulfill your present needs, vide 18 DB boost and 12 DB cut at 50 CPS and 15 DB boost and 20 DB and still provide for future ex- cut at 15,000 CPS. Features four -position turnover and $2175* pansion through use of the SS - roll -off controls. Derives operating power from the main 1B. Cross -over frequency is 1600 CPS and the system is rated amplifier, requiring only 6.3 VAC at 1 a. and 300 VDC (With Cabinet) at 25 watts. Impedance is 16 ohms. Cabinet is a ducted -port at 10 ma. Shpg. Wt. 7 Lbs. bass -reflex type, and is most attractively styled. Kit includes all components, pre-cut Héathkit Model W -5M Advanced -Design High Fidelity Amplifier Kit $3985 and pre-drilled, for assembly. Shpg. Wt. 30 Lbs. This 25 -watt unit is our finest high-fidelity amplifier. Employs KT -66 output tubes and a Peerless output transformer. Frequency response t 1 DB Heathkit Model SS -1B Range Extending from 5 to 160,000 CPS at one watt. Harmonic distortion Speaker System Kit less than 1% at 25 watts, and IM distortion less than $5975 This range extending unit uses 1% at 20 watts. Hum and noise are 99 DB below 25 watts. Shpg. Wt. 31 Lbs. a 15" woofer and a super - Output impedance is 4, 8 or 16 ohms. Must be heard to Express Only tweeter to cover 35 to 600 CPS be fully appreciated. and 4000 to 16,000 CPS. Used MODEL W-5: Consists of Model W -5M above plus Model Shpg. Wt. 38 Lbs. with the Model SS -1, it com- WA -P2 preamplifier. $81.50* Express only pletes the audio spectrum for combined coverage of 35 to High Amplifier Kit Heathkit Model W -3M Dual -Chassis Fidelity 16,01,0 CPS within 5 DB. Acrosound t This 20 -watt Williamson Type amplifier employs the famous Made of top-quality furniture- Model TO -300 "ultra linear" output transformer and uses 5881 output grade plywood. All parts are tubes. Two -chassis construction provides additional flexi- pre-cut and pre-drilled, ready bility in mounting. Frequency response is t 1 DB from $4975 for assembly and the finish of 6 CPS to 150 kc at 1 watt. Harmonic distortion only 1% your choice. Components for at 21 watts, and IM distortion only 1.3% at 20 watts. Out- Shpg. Wt. 29 Lbs. cross -over circuit included with are 88 Express only put impedance is 4, 8 or 16 ohms. Hum and noise kit. Power ra- DB below 20 watts. ting is 35 watts, $9995 MODEL W-3: Consists of Model W -3M above plus Model Shpg. Wt. 37tbs. impedance is 16 WA -P2 preamplifier. $71.50* Express only ohms. Shpg. Wt. 80 Lbs.

Heathkit Model W-4AM Single -Chassis High Fidelity Amplifier Kit *Price includes 10% Fed. Excise tax where applicable. The 20 -watt Model W-4AM Williamson type amplifier combines high performance with economy. Employs special -design output transformer HOW TO ORDER: by Chicago Standard, and 5881 output tubes. Frequency response is 1 DB from 10 CPS to 100 kc at 1 watt. Har- It's simple-just identify the kit you desire by its model monic distortion only 1.5%, and IM distortion only 2.7% $3975 number and send your order to the address listed below. at this same level. Output impedance 4, 8 or 16 ohms. Shpg. Wt. 28 Lbs. Or, if you would rather budget your purchase, send for Hum and noise 95 DB below 20 watts. details of the HEATH TIME -PAYMENT PLAN! MODEL W -4A: Consists of Model W-4AM above plus Model Shpg. Wt. 35 Lbs. WA -P2 preamplifier. $61.50* Express only Heathkit Model A -9B 20 -Watt High Fidelity Amplifier Kit Features full 20 watt output using push-pull 6L6 tubes. Built-in pre- HEATH COMPANY amplifier provides four separate inputs. Separate bass and treble tone A Subsidiary of Daystrom, inc. controls provided., and output transformer is tapped at 4, 8, 16 and 500 ohms. Designed for home use, but also fine for public $3550 BENTON HARBOR 18, MICHIGAN address work. Response is 1 DB from 20 to 20,000 CPS. Harmonic distortion less than 1% at 3 DB below Shpg. Wt. 23 Lbs. rated output. Heathkit Model A -7D 7 -Watt High Fidelity Amplifier Kit Qualifies for high-fidelity even though more limited in power than other Heathkit models. Frequency response is 1865*v 11/2 DB from 20 to 20,000 CPS. Push-pull output, and Shpg. Wt. 10 Lbs. separate bass and treble tone controls. HEATH COMPANY A Subsidiary of Daystrom, Inc. BENTON MODEL A -7E: Same, except that a 12SL7 permits preampli- $20.35* HARBOR 18, MICHIGAN fication, two inputs, RIAA compensation, and extra gain. Shpg. Wt. 10 Lbs. Please send Free HEATHKIT catalog . Heathkit Model XO-1 Electronic Cross -Over Kit. Separates high and low frequencies electronically, so they may be fed to separate amplifiers and separate speakers. Selectable cross-over frequencies Name are 100, 200, 400, 700, 1200, 2000, and 35,000 CPS. Separate level control for high and low frequency channels. Minimizes inter - Address modulation distortion. Attenuation is 12 DB per octave. $' 895 City & Zone State Handles unlimited power. Shpg. Wt. 6 Lbs. I

DECEMBER 1956 9 Sharpening Power Tools 8 -inch blade can be set with the same dulled, they can often be restored by tool used for a handsaw: Although the objective is the same a saw set, honing without removing them from - following the manufacturer's safety, accuracy, quality the force of directions. the machine. Honing is indicated when- - However, blades a rapidly turning motor makes sharp- of from 10 to 16 in. ever the jointed surface comes out in diameter are set with ness in power tools even more neces- a hammer and slightly rough or fuzzy. The process a special setting device (Fig. sary than sharpness in hand tools. So, 2) that can be accomplished while the machine from last month's discussion of putting is stationary or in motion. an edge on hand tools, let's tackle the Stationary honing ( Fig. 4) requires wrapping a fine oilstone in wax paper, job of keeping the cutting edges of BLADE machine tools as keen as they should be. leaving about a third of the stone ex- The Circular Saw: Sharpening a cir- SETTING posed. The paper will prevent the stone cular saw is very similar to sharpening STAKE from scratching the jointer table. Place a hand saw. I believe it is best for the the oilstone on the front table with the exposed end over the blade opening beginner to entrust the operation to a Fig. 2. Setting teeth of a large blade. professional, but the craftsman who has and lower the table until the stone lies been using the saw should have enough assures accuracy. Mark a starting point flat on the beveled side of the blade. and set the first tooth bent away from Wedge the cutter head rigidly in this you, followed by alternate teeth. When position and stroke the stone back and the starting point is reached, reverse the forth across the blade until it is sharp- blade and repeat the process. ened. Repeat the process on the other Crosscut, rip, and combination saws blades, using the same number of are filed with the existing bevel setting strokes. the pattern. The blade should be held To hone while the machine is run- in a clamp to prevent vibration. Mark ning ( Fig. 5 ) , front and rear tables a starting point and, using a flat mill should be level with each other at the file with rounded edges, take light highest point of the cutting arc. Clamp strokes as you file the teeth bent away a wooden stop block across the front from you (Fig. 3 ). Be sure to use the same bevel as a guide. The rounded edges of the file will keep the gullets round; square gullets might cause the Fig. r. Jointing a circular saw blade. blade to crack. When you have circled the blade, reverse it in the clamp FRONT TABLE understanding of the blade to tackle the and proceed as before. job. Four operations are involved - Jointer Blades: When jointer blades jointing, gumming, setting, and filing. need sharpening by grinding, it is wise To joint the saw (make the teeth uniform in height), reverse the blade on the arbor, raise the table above the center of the opening in the table at right angles to the blade (Fig. 1 ) . Start Fig. 4. Stationary honing of a jointer. the motor and slowly lower the table until the saw teeth barely touch the table immediately in front of the blades. oilstone, causing sparks to fly. Shut With paper wrapped around the oil- off the motor and examine the blade stone, place it on the table over the to see if all the teeth have been touched blade opening and against the stop by the stone. If they have, your saw block. Holding the oilstone securely, is perfectly round; if not, repeat the lower both tables until the blades FILING process. VISE lightly touch the stone. Slide the stone After a saw has received many filings, back and forth across the full width Fig. 3. Filing teeth with a mill file. of the gullets between the teeth become the opening several times. Shut off the shallow and frequently clog up with to take them to a professional. How- motor and check the edges of the blades. sawdust or resin. This gumming can be ever, there is much the amateur can do You will notice that a new narrow bevel removed with a thin emery wheel or to keep them in condition before such has been formed. It should not be a file, but a simpler method is to soak action is necessary. Before feeding any more than 1/32 in. in width, or the the blade in turpentine overnight. stock through the jointer be certain that machine will not operate smoothly. As with a handsaw, setting the teeth the wood is free of any surface grime Shaper Cutters: Ho .e only the flat makes the kerf wide enough to prevent or imbedded matter which will damage side (the face) of a shaper cutter by the saw from binding in the wood. An the blades. When they seem to have working it back and forth, first on the

IO AUDIOCRAFT MAGAZINE coarse side of an oilstone, and then on the fine side (Fig. 6) . To finish, stroke the beveled edge very lightly with a fine oilstone to remove the wire edge, but use extreme caution not to change the shape of the cutter. Mortising Chisel: The mortising chisel, which adds so much to the ver- satility of a drill press, can rely upon the drill press to keep it in topnotch cutting condition. The mortising, or hollow, chisel is comprised of four cutting edges forming a perfect square - actually four chisels in one. To simplify sharpening and assure a uniform bevel, fasten a cone -shaped grinding wheel

Fig. 5. Honing revolving jointer blades. Only planned high fidelity in the chuck of the drill press. Using a machinist vise or a clamp, secure the give high fidelity! chisel in an inverted position directly can you true

beneath the point of the stone (Fig 7) . Be certain that the chisel is at an angle of exactly 90°, then lower the revolving grinding wheel slowly and sharpen the four inside cutting edges in one opera- Putting together a hi-fi system for your limitless. We're happy to help you tion. Since the cone cannot reach into home can be simple-and it probably choose what will best suit your borne the extreme corners of the chisel, they will cost a lot less than you think! and your budget. You can start small should be finished afterward with a Here at MusiCraft we offer the kind and add as you wish. square file. As a final touch, hone the of information and guidance that will Stop in at MusiCraft soon or write outside surfaces very lightly with a fine oilstone. Bits used with a hollow chisel help you get started right and avoid us for further information. Let us help are sharpened by the same method as mistakes. - you plan the kind of high fidelity explained last month for regular wood- As you may know, possible combi- system that will give you true high working bits. Using a small, flat auger - nations of components are practically fidelity. bit file, sharpen the inside of the spurs following the arc of the edge; file the Send now for FREE NEW HIGH FIDELITY CATALOG: Here's a special high fidelity catalog that you'll find particularly useful, because we have included only equipment which we at MusiCraft consider the best - from the standpoint of compatibility and stable operating efficiency - in every price range. Page after page pictures the newest high fidelity equipment with detailed informa- ºgt fidelity catalog tion about characteristics and specifications. Fig. 6. How to sharpen a shaper cutter. cutting edge of the lips on the side toward the shank of the bit. The Oilstone: Because so much re- sponsibility rests upon the common oilstone in keeping both hand and power tools razor sharp, let's give a thought to 48 East Oak Street Chicago 11, Illinois DElaware 7-4150 getting the most from that valuable, but inexpensive, implement. The best type of stone for all-around home -workshop Lowest Prices Largest Component Selections Complete Custom Installation Service Continued on page 43 DECEMBER 1956 II THIS NEW STEREO TRIPLE PLAY HEAD DOES IT- The 36ST Berlant Deluxe Recorder is ideal for radio Plays Full Track, Half Track, Stereo station use. Delivers performance characteristics for the most exacting quality use. Hysteresis synchronous drive model - (99.8% timing accuracy). Frequency response 40 to 15,000 cps at 15 ips ± 2db. Save the cost of TRIFLE PLAY a second recorder plus savings HEAD HALT TRACK in space, operator time and RECORD

tape. Perfect for the station HALF TRACK planning stereo tape ERASE FULL broadcasts on AM and RECORD K FULL TRACK FM simultaneously. ERASE

Head Compliment Model 26ST and Model 36ST. Another exclusive development For the Advanced of the superb engineering laboratories of American Electronics - America's Audiophile foremost manufacturer of electronics for military, home and industrial use. the Concertone Custom Recorders answer recording and playing needs for years to $50.00 worth of recorded tape with come. Full professional FREE- features include use of 103x 1. the purchase of any B -C recorder. reels, editing and cueing, SA VE-$73.50 on a new $93.50 Concertone 431 signal level meter, 3 motors, tvEEuRo Custom monitoring from tape 6Y NGETON 2. Microphone. while recording, Ot,.GJ Offers limited and may be withdrawn with- 2 channel input mixer. out notice. See your Berlant-Concertone ER r,S;RButCR distributor today for your FREE tape library or for the microphone savings ... featured at Take Time to Pay... the dealer stores listed on opposite page. Terms to meet your budget Write for new 6 -page brochure No. 22-D. on all models. (Model 22) As low as $49.50 down, $7.50 Audio Division, per week, 24 months to pay. AMERICAN ELECTRONICS, INC. - 655 West Washington Blvd. Los Angeles 15, California

I2 AUDIOCRAFT MAGAZINE The following Berlant-Concertone distributors invite you to visit their store to see the new TRIPLE PLAY RECORDERS and/or get your free $50.00 tape library or Concertone Custom Microphone for $20.00 with purchase of any Berlant- Concertone recorder.

AKRON LAFAYETTE, INDIANA PHILADELPHIA Audio Hall Lafayette Radio Almo Radio 326 W. Bowery St. 408 North Street 412-16 North 6th St. Olson Radio Warehouse Inc. LAKEWOOD, 509 Arch St. 73 E. Mill Street OHIO Music Unlimited Radio Electric Service ALBUQUERQUE 13410 Detroit Ave. 709 Arch Street Hi Fi Equipment Inc. PHOENIX 816 San Mateo S. E. LAS VEGAS Audio Specialists Nevada Book & Sound Sound Engineering & Equipment Co. 333 E. Camelback Road E. 3011 Monte Vista, N. E. 306 Charleston Radio and Sound Supply Co. PITTSBURGH, PENNSYLVANIA BEVERLY HILLS 25 E California St. Concerto Room, Inc. Crawfords of Beverly Hills 642 Grant St. 456 N. Rodeo Drive LONG BEACH, CALIFORNIA M. N. Mansfield Co. Dackney Electronics BINGHAMPTON, YORK 937 Liberty Ave. NEW 343 East Market Street Morris Distributing Company Radio Parts, Inc. Scott Radio Supply, Inc. 6339 Penn Ave. 195 Water Street 266 Alamitos Avenue PORTLAND, OREGON BROADVIEW, ILLINOIS LOS ANGELES Hi-Fi Unlimited Meier and Frank Co. Beverly Hi-Fi Sandy's Stores 1305 Roosevelt Road Camera 468 So. Robertson Blvd. 714 S. W. Washington Street BROOKLYN Bushnell Electronics Brooklyn Hi RED HOOK, NEW YORK Fidelity Sound Center 12026 Wilshire Harter, Inc. 836 Flatbush Ave. to Gateway Music 10 South Broadway BUFFALO 3089 Wilshire Blvd. RIVERDALE, ILLINOIS Buffalo Audio Center L. A. Portable Recorders Arrowlite Co. Inc. 521 No. La Cienega Blvd. Audio Distributors 14218 S. Indiana Ave. 153 Genessee Street Midway Electronics 2817 Crenshaw Blvd. RIVERSIDE, CALIFORNIA CANTON, OHIO Sound Unlimited Burroughs Custom Music Radio Inc. 6320 Commodore Sloat Drive 3980 Main 2705 Fulton Road, N. W. Street The Camera Center MADISON, WISCONSIN SACRAMENTO 331 Cleveland Avenue Hi-Fi Corner Hi-Fi Sound Supply 1910 - 16th Street CENTRAL CITY, NEBRASKA 401 State Street Sampson Electronics MIAMI ST. LOUIS, MISSOURI 102 G. Street Hi-Fi Associates Van Sickle Radio Company 1113 Pine Street CHICAGO 3888 Biscayne Blvd. Continental Corporation SALT LAKE CITY MILWAUKEE Sound by Craftsmen 3239 W. North Fi House, Inc. Hi 358 South 3rd East Electronic Expediters, Inc. 2630 N. Downer Street 2909 W. Devon Avenue Photoart Visual Service SAN DIEGO Hi-Fi Inc. 840 No. Plankinton Ave. Breier Sound 10309 South Western Ave. Wack Sales 3781 Fifth Street Newark Electric Company 3131 W. North Avenue Recording Center 223 West Madison Ave. 1342 - 5th Avenue Voice & Vision MINNEAPOLIS Wright's House of Hi-Fi 53 E. Walton Place Electronic Industries, Inc. 5140 El Calon Blvd. 2451 Hennepin Avenue CINCINNATI Paul Schmitt Music Company SAN FRANCISCO Inc. San Francisco Customcrafters Audio 68 South Tenth Street Radio & Supply Co. 2259 Gilbert Avenue 1280-84 Market Street Steinberg's Inc. NEWARK SAN MARINO, CALIFORNIA 633 Walnut Street Hudson Radio & Television Corp. E. O. Bulkley Co. CLEVELAND 35 William Street 2533 Mission St. Audio Craft Co. Radio Wire Television Co. Central Ave. SAN PEDRO 2915 Prospect Ave. 24 Bower's Music National Manufacturing Co. NEW YORK 810 So. Gaffey 1000 Hamilton Ave. Airex Radio Corporation SANTA BARBARA The Progress Radio Supply Co. 64 Cortlandt St. 413-415 Huron Rd. Pacific Audio Supply Asco Sound Corp. 2919 De La Vina Street COLUMBUS 115 West 45th Street Third Floor SEATTLE Shaffer Music Company Seattle Radio Supply Inc. 849 North Street Audio Unlimited, Inc. High 2177 - 2nd Avenue DAYTON 119 East 59th Street Goody Center, Inc. Ta l l's Custom Electronics, Inc. Audio 235 W. 49th St. 1415 Third Ave. 1000 South Main St. 250 W. 49th St. STOCKTON, CALIFORNIA DENVER Grand Central Radio Quality Sound Service Electric Accessories 124 East 44th Street 1217 North Wilson Way Stout at 20th Street Heins & Bolet TOLEDO DETROIT 65 Cortlandt Street Hudson Radio & Television Corp. Jamiesons High Fidelity Haco Distributing Co. 840 W. Central Avenue 9730 Burnette 48 W. 48th St. 212 Fulton St. Torrence Radio, Inc. K.L.A. Laboratories, Inc. 1314 Madison Avenue 7375 Woodward Ave. Leonard Radio Co. Lobby -Hobby, Inc. 69 Cortlandt St. TOPEKA, KANSAS 17300 Woodward Ave. Liberty Music Shops Plaza Television 450 Madison Ave. 140 S. Huntoon EAST CHICAGO, INDIANA Peerless Camera Stores TUCKAHOE, NEW YORK J. N. E. Television 138 East 44th Street 2013 Broadway Boynton Studio Radio Wire Television, Inc. 10 Pennsylvania Avenue 100 Sixth Avenue HEMPSTEAD, LONG ISLAND TUCSON Island Audio & Hi Fi Center, Inc. Recording Wire & Tape Co. Art Electronic Supply Co., Inc. 441 Fulton Avenue 163 East 87 Street 145 South Park Newmark & Lewis Sun Radio & Electronics Co. Inc. Ave. 43 Main Street 50 W. 20th Street VAN NUYS Terminal Radio Corporation Valley Electronic Supply Co. HOLLYWOOD, CALIFORNIA 85 Cortlandt Street 17647 Sherman Way Hollywood Electronics 7460 Melrose Ave. ONTARIO, CALIFORNIA WASHINGTON, D. C. Magnetic Recorders Rudi Pock - The Original Hi Fi Shop Electronic Wholesalers 7120 Melrose Ave. 604 N. Euclid 2345 Sherman Avenue, N. W. Pacific Hi Fi PASADENA Kitt Music Company 1320 Cahuenga Blvd. Audio Associates 1360 G. Street N. W. HOUSTON 689 So. Fair Oaks Sun Parts Distributors, Ltd. Audio Center Inc. Dow Radio 520 - 10th Street N. W. 1633 Westheimer 1759 E. Colorado YONKERS Busacker Electronic Equipment Co., Inc. High -Fidelity House Westlab 1216 West Clay 536 So. Fair Oaks 2475 Central Park Ave.

DECEMBER 1956 13 0 W aim by J. Gordon Holt

Testing Recording Tape record head. But it is not often realized properties will determine its suitability that the critical bias-current setting is for the recorder. To hear the differences between two what accounts for most of the observ- The physical characteristics of a tape loudspeaker systems it is only necessary able differences between recording tapes. (as distinguished from its magnetic to switch back and forth between them For instance, if a recorder has its properties) will affect its performance while playing some appropriate program bias current adjusted to obtain maxi- only indirectly, in dependability, material. Assuming the speakers to be mum output at 400 cps from an aver- smoothness of motion, and durability in of similar efficiency, the differences age oxide formulation, the tape will be use. It might be well to consider them heard will represent accurately the dif- found to require about 23 db treble for a moment before getting to the ferences between the speakers. boost at 15,000 cps to obtain the matter of performance testing. But comparing two brands of record- NARTB tape-recording characteristic. The ideal recording tape is imper- ing tape is another matter altogether. With the record equalization so set, a vious to breakage in normal use. This Even though it is simple enough to A -B narrow -gap playback head will give flat is self-explanatory, and in practice re- two brands of tape by splicing a length high -frequency response from that tape quires only that the tape's tensile of tape A to a length of tape B, and with the 3,000 -cps NARTB playback strength be greater than the most severe then recording through the splice, the curve. But if we record on a tape that pull that is likely to be encountered audible difference between them is not requires a higher bias current than this, when braking from the fast -forward or likely to give any indication as to the the result will be a considerable rise rewind mode of operation. relative quality of each tape. It is, in- in high -frequency output, at slightly A tape should not assume a perma- stead, likely to indicate only that the re- nent stretch before snapping under ten- corder is more closely adjusted to the x sion. All tapes will stretch to some characteristics of one tape than to those extent, but the less permanent deforma- of the other" tion that takes place before a break So far as magnetic properties of the occurs, the easier it is to repair a break oxide coating are concerned, there is perfectly. A break can be spliced, but really very little difference between the a decrease in pitch because of tape potential quality of one recording tape be and another competing brand. Adver- elongation cannot corrected. Ideally, a tape should be unaffected tising claims of vastly improved high - by extremes of temperature and humid- frequency response and lower distortion ity. This refers to physical changes in should be viewed with some suspicion, higher -than -normal distortion and with the tape, such as loss of tensile because there have been few radical slightly lower -than -normal output. On strength or tendency toward developments in oxide formulation dur- direct comparison the second tape could cupping when be said to have "vastly improved high - humidity increases. All tape will print ing the past 5 years. With the outstanding exception of Scotch No. 120 frequency response", but in view of the through from layer to layer under extreme climatic conditions, high-output tape' (which is unlike any- resulting loss of output and increase in but if the tape remains physically it thing else currently available), nearly distortion, this could hardly be con- unchanged can at least be used all brands of recording tape are essen- sidered an unalloyed advantage. again. The ideal tape has tially the same in high -frequency re- Several tape manufacturers have taken uniform coating thickness and thickness sponse, distortion, and output character- advantage of the fact that their tapes base through- istics. require higher than average bias cur- out an entire reel, and from one reel This is not to be construed as mean- rent, and have touted the rising high to another. Variations in base thickness ing that they are identical in charac- end as evidence of a superior product. can cause uneven winding at high speeds teristics under the same conditions, for This is unfortunate because some of and tend to reduce the tensile strength the magnetic properties of the coating them have been proven outstandingly of the tape. Varying thickness of the oxides used are quite different from one good in all respects when used with the coating will cause changes of output level brand to another, and the physical char- correct bias current. There is really and variations in frequency re- acteristics of competing brands differ no need for indulgence in such mislead- sponse within a reel or between different reels. significantly also. ing comparisons. All recordists who have looked into This does serve to show, however, that Further, the ideal tape has edges that the theory of tape recording know that the choice of recording tape for home are perfectly smooth and perfectly straight. Small nicks or a tape's output level, distortion, and use can be important in terms of per- rough spots frequency response are intimately related formance. If the tape recorder is along the edges of a tape provide easy starting points to the bias current supplied to the equipped with a variable bias control, it for breakage under ten- can be matched to any tape, so the sion, while a tape which is not cut proper choice of a tape will depend straight will wind unevenly and scrape 'Scotch No. 120 has a slightly lower bias requirement and produces 8 to 12 db more output ( with mostly upon its physical quality ( which on the reel flanges. no increase in noise level) for a given input will be Another qualification of the ideal tape signal than do other varieties of tape. Conse- discussed later). If the bias quently somewhat different test procedures must current is nonvariable or is not easily is standard width throughout the entire be used when comparing it with competing varieties. adjusted, though, the tape's magnetic Continued on page 35

14 AUDIOCRAFT MAGAZINE Readers' EDITORIAL AT the back of this issue will be High Fidelity Music Shows. These are found a comprehensive index for actually full-size audio shows done in Forrnni- - Volume 1 of AUDIOCRAFT Magazine. the conventional manner: one or more Gentlemen: Vol. 1 consists of the first 14 issues, floors of a major hotel are taken over from 1955 to December by J. Gordon Holt seems to have a talent November the show management for the dura- 1956 inclusive; future volumes will be for hitting on topics to which I have tion of each show; rooms on these particular sensitivity. In this instance composed of 12 issues each, from Janu- floors are rented to all manufacturer - ary through December of each year. exhibitors on a first -come first -served I have no complaint with what he has Even we were surprised, as we proof- basis; adequate publicity is obtained be- said; I only wish he had said more. read index, the amount of fore In his column starting on page 12 of the at valu- and during the show. Each show is able material it represents. for three days the June issue of AUDIOCRAFT, he wrote reference open from 1:00 to 10:00 We have copies of only a few P.M., about a subject of particular interest extra giving everyone a chance to at- wise, to to those of us who broadcast "good" issues; it would be then, pro- tend. One additional idea worth noting tect your file of AUDIOCRAFT. Possibly is that, while is in music on a commercial basis. Our pro- each show progress, grams are made up principally of com- the best way to accomplish this is to exhibiting manufacturers may participate bind it in mercial disc and tape recordings, plus by volumes. It happens that lecture -demonstrations of complete sturdy, those tape recordings which we can good-looking binders are avail- sound systems given periodically in a make ourselves. Generally speaking, we able for Vol. 1, at $3.50; ordering in- nearby auditorium. obtain the commercial recordings directly formation is given on page 1 of this Seven Rigo shows were held (in from the manufacturers or their agents issue. Columbus, Cincinnati, Atlanta, Miami, with the understanding that they are New Orleans, Dallas, and St. Louis ) solely for broadcast use with label during the latter part of 1956. Al- and/or artist credit suitably given. Our though manufacturers were reluctant to own recordings usually are even more participate at first, the enthusiastic ap- restricted in use perhaps we agree proval - and heavy attendance - with - which only to use them a limited number of the public responded changed times, or not to use them commercially, their minds, and many are now taking or perhaps they are subject to perform- part. There seems to be little doubt that the enterprise will ance fees. It is difficult to make a THIS is being written in the middle succeed. There are eleven shows general statement. Then too, we pay of the Audio Show season, just scheduled for the first half of 1957: Milwaukee, substantial fees regularly to ASCAP, after the New York and Boston shows. January 4-6; BMI, and SESAC for the right to broad- Attendance records are being broken Minneapolis, January 18-20; Seattle, February Portland, cast copyright musical material. now with almost monotonous regularity. 1-3; February 15-17; Kansas City, March 1-3; The question Mr. Holt has raised is It seems to be unimportant whether an Omaha, March 15-17; Denver, March 29-31; Lake that of the tape -recorder owner who admission fee is charged or not; in New Salt City, April records our broadcasts. With' modern York, where the four -day show was 5-7; Pittsburgh, April 19- 21; Cleveland, tuners and recorders, it is possible for held this year at the new Trade Show April 26-28; and De- troit, May the home hi-fi enthusiast to make ex- Building, 31,000 paid 500 or 75¢ to 3-5. cellent recordings of our transmissions. push their ways through the jammed But what is actually the home recordist's halls. Total attendance was said to be right in such matters? Mr. Holt has 38,000. Estimated attendance at the clearly stated that a home recordist three-day Boston show was 10,000 - would be asking for trouble in putting also up substantially from last year. Ob- out commercial recordings based on viously, hi-fi interest in the major cities material picked up off the air. We is still increasing, even though it has think that the cautioning to your tape - existed there for many years. These are not small markets in any recorder -operating readers should go Far more important than record - sense. It is simply inexcusable that further than this. It is very likely that breaking attendance at the major shows, efforts have never before been made to a listener can tape record anything that in our opinion, is the work being done reach them and others like them. Each comes from his tuner, provided the to promote high fidelity in the second- show ought to leave a spark of interest taping is done for his own personal en- ary metropolitan areas. There have been large enough to grow healthily, forming joyment, without getting into serious several one -evening demonstrations and the nucleus of a local hi-fi boom. It trouble. Even here, though, if one were lectures in various cities which have will take only a few dozen such expand- to tape just the music from a recording achieved notable success. Unfortunately, ing circles of interest to make aware- with the intention of avoiding the they have been necessarily limited in ness of high-fidelity sound truly nation- purchase of the recording, it is my im- effect because of sponsorship by a single wide. We believe that Rigo and the pression that the record company, if it dealer, manufacturer, or manufacturer's manufacturers co-operating with them ever found out about the unauthorized agent, or by a very small group of them. should be congratulated on their enter- taping, could and possibly would sue It is manifestly impossible to produce prise and vision. We wish them in- the offending recordist. A tape re- an expensive full-scale audio show creasing success. Finally, we hope that cording taken from a broadcast and under such circumstances. Every one all readers living in or near one of used commercially in any manner (such of these affairs helps, but promotion these scheduled show areas will spread as background music in a restaurant or on a grander scale is needed. the word among their friends, and will for another radio broadcast) certainly It is being provided now by an attend the show themselves; even long- could involve the recordist in legal independent organization known as time audiophiles will find an audio Continued on page 44 Rigo Enterprises, Inc., producers of show a unique experience. - R.A.

DECEMBER i956 5 by JOHN J. STERN, M.D. ... build an AM crystal tuner

THE schematic diagram for the AM speaker, the poor frequency response 1 .05-µfd paper capacitor. crystal tuner described here was becomes a serious drawback. The crystal 1 100-K 1/2-w resistor. first published in a Sylvania booklet, tuner provides a remarkable improve- 1 1N34A germanium diode. 40 Uses for Germanium Diodes. It ment in the quality of AM reception. 2 phono jacks. seemed to be the answer to a problem Selectivity of the tuner is excellent; 1 ground lug. which has plagued many music lovers the volume, while not sufficient for 6-32 screws and nuts. depending on AM radio - the relatively headphones, is more than ample to drive Hook-up wire. poor design of AC -DC AM table radios an amplifier; and a careful listening test Chassis, 2 by 91/2 by 5 in. which are so frequently used as AM will reveal a beautifully smooth, crisp, tuners in otherwise high-fidelity music wide -range quality which, with a good Construction Notes systems. Since the chassis is usually station, comes close to the character An AM tuner of this sort is quite of FM. The tuner is, of course, only simple in design, as the schematic ANTENNA DUAL ANTENNA COIL 365.NÁ D COIL 1N34 capable of bringing in stations within diagram in Fig. i shows. It consists a radius of about 25 miles, and an only of a tuning section, to pass a antenna is needed. I used one lead of desired station frequency and reject all TO others, and a detector circuit. A ger- AMP. the FM antenna, and no ground was necessary; the amplifier seems to act as manium diode ("crystal") is used as ANTENNA an efficient ground. Faint reception of a detector; this, with an RC filter, re- some stations 50 miles away promises moves the radio -frequency component GROUND satisfactory pickup with a correct an- of the desired signal passed by the tenna. tuning section, and the remaining audio modulation is fed to the output jack. NEGATIVE MUTUAL COUPLING COIL Parts List The circuit's simplicity is possible Fig. r. Circuit of diode tuner is simple. 2 shielded antenna coils, Miller type because no amplification is provided 242-A. either for the radio frequency or for above AC ground potential, using such 1 negative mutual coupling coil, Mil- the detected audio signal. Accordingly an AM radio as a tuner introduces hum ler type EL -56. it is inexpensive (total cost for parts, into the system which can become an- 1 365-µµfd two-gang variable ca- including chassis, is less than $9) and noying, even when the radio is not pacitor, Miller type 2112 or equivalent. easy to build. Further, because it does used but the record player or tape 1 .01-µfd mica capacitor. not tune sharply, no high audio fre- recorder is operating. It can be danger- 1 .005-µfd mica capacitor. quencies are lost; the full range of ous as well. Careful polarization of AC 1 .00025-µfd mica capacitor. Text continued on page r8 power plugs can reduce the hum, but with AM tuner, FM tuner, record player, tape recorder, and amplifier plugged Fig. 3. Diagram showing parts wiring under the chassis. Lead dress isn't critical. into the same outlet, the probability of correctly positioning each plug in re- ANTENNA COIL lation to all the others, and keeping it that way, is almost negligible. TO TUNING CAPACITOR A crystal tuner is independent of TRIMMERS 60 -cps AC current, since it contains no tubes that require a power supply, and it was anticipated that its use would eliminate hum. It did. Not anticipated, but welcome, was the improvement in over-all performance to a remarkable degree. It seems that even a good AM table model is so designed that the high frequencies are attenuated. This inten- tional restriction compensates for the necessarily poor low -frequency response in a small set with a small speaker, producing better balance, and also hides ANTENNA the severe distortion. But when the INPUT detector section of the radio is used as a tuner driving a good amplifier and

16 AUDIOCRAFT MAGAZINE Fig. 2. Chassis Munching template for Dr. Stern's tuner. This is full-size, so that no scaling or layout work is necessary.

DECEMBER 1956 17 Continued from page i6 is heavy. This will shave another dollar off the price. We used a commercial the station's modulation is retained. chassis base 2 by 91/2 by 5 in.; a full- There is nothing the tuner likely to in size chassis punching template is given wear out or become defective, so it in Fig. 2 for those who use the same should last indefinitely without main- size chassis. tenance. Parts are mounted as shown in the There are some disadvantages too, as photographs, with the two large an- must be expected. The of very lack tenna -coil cans at each end and the small coupling -coil can behind the tuning capacitor in the center. A standard phono jack is used for the antenna connection, but a lug -type terminal board may be substituted with an appropriate change in the punching template. Both this and the audio -output phono jack are insulated from the chassis, all ground connections being made at a single point by means of a ground lug. The Final assembly of the Miller 565 kit. Antenna and output jacks on rear apron. wiring is shown clearly in the pictorial diagram, Fig. 3. high -frequency end of the broadcast amplification makes the tuner useless It took us 31/2 hours to lay out, band, and the small trimmer screw at in fringe areas, say beyond 25 miles scribe, and cut the chassis holes, mount the back end of the tuning-capacitor from stations of average strength and the parts, and do the wiring. If the assembly is adjusted for greatest sound 40 miles from high -power stations. template (Fig. 2) is used, the job volume. If a dial is used, the pointer Even within these areas a long outside should be shortened considerably. We is turned to read the frequency of a antenna must be used, and the tuner's didn't attempt to add a dial, dial pointer local station (at the upper end of the output must be fed to a high -gain am- and knob, but it could be done easily; band, preferably) ; the trimmer screw plifier or the microphone input of a dial assemblies are available at nominal at the front end of the tuning -capacitor preamp-control unit. A crystal tuner is cost. assembly is adjusted until the station is heard with greatest volume, and then AUDIOCRAFT Test Results the rear trimmer is adjusted for greatest Here in Great Barrington there are no sound volume. local stations on which the tuner could be tested. Taken to a few nearby cities, The Miller 565 Kit however, it worked perfectly well. The tuner described by Dr. Stern Stations located in any given area are worked so well that we became curious usually well separated in frequency, and about the Miller model 565 AM tuner the tuner had no difficulty in discrim- kit, which is priced at $14.70. It is inating between them. Sound was wide - available completely wired and ready range (how wide depended on the to operate, as the Model 595, for Coil cans and tuning gang mount on top. station) , clear, and free of hum and $19.50. We obtained the kit and built buzz. it also. not free of the usual AM troubles - Alignment is quite simple. If no Examination of the schematic dia- static, fading after dark, and beat dial is used, the tuning capacitor is gram for the 565 showed it to be almost whistles and may, indeed, be more - adjusted to receive a station at the Continued on page 43 susceptible to them than standard tuners. if its distance limitation does not Still, Detail of parts on back side of laminated wiring panel in the 565 AM tuner kit. affect you, a crystal tuner offers a most inexpensive way to obtain AM fidelity better than that provided by any con- verted radio, and at least as good as that of most hi-fi AM tuners. A high-fidelity AM tuner having an infinite -impedance

This corresponds to pictorial, Fig. 3. detector, however, will probably have lower distortion. It is possible to make your own chassis of fairly thin sheet aluminum, since none of the parts to be mounted

Ió AUDIOCRAFT MAGAZINE by Dr. JOHN D. SEAGRAVE Part I

MINIMIZING PICKUP TRACKING ERROR

THE serious audiophile has been perfectly traces the groove. The groove rived it with reference to an illustration warned by discussions of the prob- can then be treated as a mathematical of a simple sine wave. It is, however, lems of pickup design to recognize the curve. The problem may be stated an implicit equation giving O as a func- importance of minimizing "tracing" simply: if s is the distance along the tion of 0', while we want to find O' as a distortion in playback - failure of the groove axis, and y(s) the displacement function of O. Higher mathematics is stylus to trace all the details recorded of the groove at s, what is the displace- required for its exact solution, but in the groove - by proper choice of ment Y(s) of a stylus constrained to fortunately an extremely good approxi- stylus force, and leveling or balancing move in a line making an angle a mate solution will serve our purpose. of the pickup arm. He also knows that (alpha) with the y-axis? An exact solution of Eqn. (5) for a sine for minimum nonlinear electrical output The general problem just stated will wave is available2 in terms of a series of from the pickup, the stylus tip and now be illustrated for the simple case Bessel functions, but for the small damping material must be in good con- of a recorded sine wave. In Fig. I the distortions we are considering (e less dition and the magnetic circuit clean solid curve is such a sine wave of ampli- than o.x), the exact solution differs by and symmetrical. It seems to be widely tude a constructed geometrically in less than one part in a thousand from assumed that if he parts with another terms of an angle O (theta), which we the very much simpler expression, thirty dollars or so for a piece of hard- may identify with zlrs/X if X (lambda) is the Y(0) = (a/cosa)(sinO + %e sin2O). ware known as a "tone arm" in which wave length of a full cycle. Mathe- ..(6) to plug the pickup, and solemly ob- matically, serves the suggested ritual for mounting y(s) = asin(O = 27rs/X). ... (I) The Distortion Index the arm, his worries about "tracking Now if we draw through the point s a Let us rewrite the distortion parameter error" (failure of the pickup axis to be line making an angle a with y(s), it e (epsilon) in' more convenient terms. tangent to the record groove) are at will intersect the curve at a point s'. The wave length X = V/f, where V is an end. Hear, then, the sad factsl: The displacement Y(s) along the in- the groove velocity and f the frequency. few of the commercially available arms clined line is plotted a s a function of s 27rf = w (omega), and wa = n is the are designed to give minimum tracking distortion on the largest LP's they are supposed to handle! Distortion arising from tracking error can run up to to% on loud passages with certain combina- Groove Axis tions of popular arms and cartridges, or more if they are carelessly mounted. It is the purpose of this article to show how optimally designed (or modified) arms can give less than 1% tracking Fig. 1. Graphical construction of a sine wave, and the corresponding distorted wave gen - distortion, or how a commercial arm erated by a tracking error of 30°. can best be mounted to give the least distortion possible for its nonoptimum for the deliberately exaggerated case of a transverse recorded velocity. If St (capi- offset angle. tracking error a = 30 °. Its maximum tal omega) is the turntable angular Nature of the Distortion amplitude is a/coca, and its distorted velocity and R the radius of the groove, shape may be recognized as differing V = RSl. Noting finally that tana '' a The distortion of a single frequency re- from y(s) by a predominant second for small angles, we may write cording arising from tracking error is harmonic term, in phase with y(s). It almost entirely second harmonic, or can be seen from Fig. I that 27raa waa_(v\ frequency doubling, even for very large Y(s) cosa = y(s') and E X V ` V Ja = tracking errors. It will be shown that it s' -s = y(s') tana. . . . (2) arises kinematically as an alternating Since Y(s) has maximum amplitude - advance and retard of the reproduced a/cosa and the same period as y(s), we ( Sl / \ aR) Sl ) \ R >, .. (7) signal with respect to the recorded might describe it in terms of an artificial and, since s = RSlt and O = wt, Eqn. signal, which amounts to a frequency - phase angle O': (6) becomes modulation of the signal by itself. Y(s) = (a/cosa) sine'(s). ... (3) Y(t) Since it will be our object to develop This angle O' advances and retards with rr ¡ \ / \ means to minimize source [sin cet -}- %21 11 R sin2 wt] this of dis- respect to O. With the aid of Eqns. cosa tortion, we may treat the problem as (i) and (2), we can rewrite Eqn. (3) as a "almost linear", so that we may regard a sine' = Y(s) cosa = y(s') = ...(8) other nonlinear effects as (s' s) cota (X O) superposable, - = /27r)(0' - cota 'H. G. Baerwald, Jour. Soc. Motion Picture Eng., and the various linear playback losses 37, 591 (1941). Our Eqn. (5) is mathematically ...(4) identical with the two -body problem of celestial as having already taken place. In and finally as mechanics, in which it is desired to describe the short, we will assume that the stylus O = O' e sino', motion of a planet in terms of the phase of its - "year". The parameter e is then the eccentric- where e = (27r/a) a tana. ... (5) ity of the elliptical orbits. The solution of the i"Hi-Fi Pickup Arms", Consumer Reports 21, astronomical problem was given by Lagrange in 245-251 (May, 1956). Eqn. (5) is exact, although we have de- 1770, and more completely by Bessel in 1816.

DECEMBER 1956 19 for the amplitude of stylus motion. The Tracking Equation Interpreting Distortion Index The velocity of stylus motion is the rate In Fig. 2 is shown an arm of pivot -to - If we choose an arbitrary value of ß as of change of Y(t), designated dY/dt: stylus length L, with the stylus in a our offset angle, then the tracking dY groove at a radius R from the center of error a = 4) -ß is the distance along dt the record. The pivot is mounted at a the 0 -scale between the line 4) = ß = aw distance L -D less than the arm constant and the curve of 4) as a function coszwtl. length from the center so there is an of R for a particular value of D. For cosa [coswt+L ()() overhang D. The tracking angle (phi) appropriate values of D with fixed /3, ..J. 4) (9) is the angle between the line from pivot portions of the curve for fixed D will By comparing the second term with the to stylus and the tangent to the groove. pass on either side of the line 4) = ß first in equations (8) and (9), we see that If the axis of the pickup makes the and both negative and positive values second harmonic distortion= offset angle ß (beta) with the same line, of the tracking error will occur. Recall the difference 4 -ß = a, the tracking that it is a/R, not a, which is the index 1/2 or 1, ... (io ab) error, which is of course then the angle of distortion. In our graphical repre- (R) tcot)CR by which the pickup fails to lie along sentation this is the slope of a straight for an amplitude pickup or a velocity the tangent to the groove. line drawn from 4 = ß when R = o pickup, respectively. For either case, In the triangle SPC formed by the (the point 4) = ß on the 0 -axis) and the the distortion depends on the instan- stylus, pivot, and table center, the point on the curve under consideration. taneous recorded velocity wa, on the included angle at the pivot is 90° -0, For simplicity in illustrating the use of inverse of the record rpm S2, and on the and we may write the Law of Cosines Fig. 3, let us assume that our hypothetical tracking error divided by a the groove 2RLcos(90 ° - 95) = arm has L = io in. and that we are radius R. As we shall see, a is a function R2+ L2 - (L - D)2, talking about an LP record with inside of R, and for a given distortion a must which is simply transformed to read radius R1 = 2 in., and outside radius be smaller for the inner grooves. De- D R2 = 6 in. Then we will be interested signing for minimum distortion is ob- sinlp in the region of the family of curves 2LR + R\I 711. viously a very different matter from between R/L = 0.2 and o.6. First sup- simply minimizing the variation of a. ...(12) pose we had no overhang, or D = o. This is The Tracking Equation. gives If we put in Eqn. (rob) the values wa = It Though the curve for D = o isn't all to cm/sec, S2 = 33.3 rpm, and a/R = the tracking angle cp as a function of on the graph, it is nearly a straight line groove radius R for an arm length L degree/inch, we find 1.97% second of and 4)(o.2) = 5.7 ° and 43(0.6) = 17.5°. harmonic distortion. Then, for any If we were merely to minimize a, we other values, would choose ß = 11.6°. Then the %znd= 1.97 X value of a/R at R = 6 would be just wa 33.3 rpm a /R under 1 ° /in., which is not bad, but at R 2 it would be `Yin. How- \io cm/sec S2 deg/inch). = -3 C ( ever, if we took ß = 8.6°, the value of ... (II) a/R at both extremes would be approxi- Thus, to keep this kind of distortion mately 1.5 °/in., of opposite sign, and below 2% on a record with 33.3 -rpm numerically less at all points in between. recorded velocities over Io cm/sec, the We can do rather better than quantity (a/R), which we will call the 1.5 °/in. if we use somewhat larger distortion index, must be less than one values of ß and D. In the example degree per inch of radius. Fig. 2. Geometry of record tracking. Arm of length L from pivot P to stylus S is shown worked above a was zero only once, but We have confined our discussion so mounted with an overhang D with respect if ß and D are properly chosen, we can far to the distortion of a single sine to the turntable center C. Groove being make a positive near R1 and R2, nega- wave of angular frequency w. there tracked has a radius R. If tive between, and zero twice. Since the are two frequency w components of sign of the tracking error is of no con- and w 2, distortion and overhang D. For a fixed ß, there will be products the sequence, this will result in smaller 2w1, w2, and tracking error a ß. the nu- 2w2, w1+ Iwi-w21,asin = 4) - If maximum values. The tracking error second -order distortion arising from merator and denominator of the second at R1 = 2 should be about three times nonlinearities, but with the important term in Eqn. (12) are divided by L, it smaller than at R2 = 6, if a/R is to be difference that the terms of tracking is clear that cß can be expressed as a about the same. Suppose now we distortion are weighted by their individual function of R IL and D/L, which means had ß = 21 °, and D = o.6 in. Then frequencies, or, for a velocity pickup, by that it is possible to construct a universal a = 2° at R1 = 2, a = -1° at R= the squares of their frequencies. It is graph of Eqn. (12), applicable to any 3.2, and a = 2.4° at R2 = 6, and the fortunate that records are made with a arm. In Fig. 3, cß is plotted in degrees corresponding values of a /R are 1, 0.3, pre -emphasis requiring rolloff in play- as a function of the ratio R/L for various - and +0.4 ° /in. If ß were larger or D in general values of DIL. The range values back, but the frequency= of smaller we could reduce the largest of plotted is appropriate to all weighted character of the distortion ostensibly these at the expense of the smaller, and terms will lead to a form of intermodu- "high-fidelity" arms, and many other continue by trial and error until all three distortion forms record-player. Fig. 3 is repro- lation much larger than the of extremes had the same numerical value, -frequency harmonics duced in fine detail since it is a universal single we have the middle one of opposite sign. An- calculated, with a correspondingly larger family of curves and can be used to find ticipating one of the results of a later value. Two percent the distortion index variation any nuisance second of section, where this "optimum" condi- harmonic in loud passages arm it is desired to analyse. The plots distortion tion is calculated, let ß = 20.1° and may go unnoticed, the associated are accurate to within 0.1 degree, and but D = 0.53 in. Interpolating a curve linear interpolation may intermodulation of complex signals be made for for D = 0.53, we find a = 0.9, -1.4, may be quite serious. It is for this intermediate values of D/L. The uni- and 2.7 ° at R = 2, 3.1, and 6, respec- reason that the distortion index (a/R), versal curves are of course the same as tively. All three maximum values of to which the IM as well as the harmonic the specific curves for a to -inch arm, a /R are numerically equal to o.45 ° /in., distortion is proportional, must be kept if the decimal points are moved over one as small as possible. digit to read R and D in inches. Continued on page 34

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The distortion index m is the slope of a straight line connecting the point 0= ß on the 0 -axis with a point on the curve corresponding to the overhang D.

DECEMBER 1956 2I The MIT Chapel is a windowless brick cylinder-shaped building with a surrounding moat. Photos below show interior construction.

Recording at MIT

WHEN Kresge Auditorium and the MIT Chapel were completed in the sprini of 1955, it was demonstrated beyond doubt that the fascinating study of acoustics is now more. science than guesswork, and more than ever art. 3oth buildings are renowned for their simple nesuty, which reflects the atmosphere of Massachusetts In- stitute of Technology in the finest of modern a:chi- tectural techniques. Moreover, both were cesigned specifically ro provide the excellent acoustical characteristics that have been obtained. Designer were Bolt, Beranek, and Newman. Kresge Auditorium is a domed structure cf ajout 35o,000 cu. ft., wood -paneled over much of its interior. About x,000 sq. ft. of the rear wall is covered by a 6 -inch layer of glass fiber which is facec by woven plastic. Reflective "cloud" panels below the ceiling are adjustable, and affect sound gaalit-v to some extent. Continued on ¢.pge 34

View of the chapel altar, backed by toplighted screen. The ceiling is shaped like an inverted cone mounted off -center, and brick walls are curved irregularly to diffuse sound.

Sound -absorbent material is behind grilles in tige wall. Recording Handel organ concertos in chapel; Lawrence Moe is organist.

22 AUDIOCRAFT MAGAZINE Cross-section of Kresge Auditorium, with an exterior view at the right. Concrete dome has three primary suspension points.

Interior of Kresge Auditorium. Holtkamp organ has positiv, great, and pedal pipes entirely open to view; only swell pipes are enclosed. Auditorium and chapel are virtually ideal for recording, and served for recent Music at MIT series of Unicorn releases. Below at right are chapel layout plans.

IMiWflilllNIMMnit+5maa

loger Voisin and his brass ensemble recording in the Auditorium by George L. Augspurger LOUDSPEAKERS and ENCLOSURES

IV: Horns and Horn Enclosures

IN this series of articles so far we have perimenting with horns. In the August any other good acoustic-engineering discussed two basic types of loud- issue of AUDIOCRAFT we credited much text. In this article, however, I will con- speaker enclosure: the infinite baffle and of the original work in twin-cone loud- tinue to talk about shape and flare con- the tuned -cavity (bass -reflex) system. speakers to Mr. Voigt. The present stant since these terms seem to indicate Provision is made in each system to acceptance of horn -type systems can also well enough the distinction between the offset the loss of lower frequencies, be traced, in part, to this British de- two elements. which is an inevitable property of fairly signer. Voigt and others discovered The flare shape affects the acoustic small sources of sound, by means of that a properly designed horn acts (over impedance at the throat of the horn. resonance. The infinite baffle depends a limited frequency range) as an acous- Various shapes may be used, but the on increased cone amplitude at reso- tic transformer to correct the impedance most common in high-fidelity design is nance to even out its frequency curve, while bass -reflex enclosures effectively FOLDED HORN add radiating area to the speaker over a limited range of bass frequencies. CURLED We have also mentioned that the HORN efficiency of cone speakers is quite low - on the order of 3% to 4%. Part of the bass loss and the generally low efficiency can be traced to an acoustic mismatch between the speaker system and the surrounding air. As P. G. A. H. Voigt explains, "Most people concerned A with speakers think only of the four Fig. 2. Two variations of low -frequency horn. major items: magnet, voice coil, diaphragm, and some means of baffling the mismatch between a cone -type loud- the exponential curve. The reason is sound pressure in its efforts to take a speaker and the surrounding air. More that the exponential horn loads a short cut from side one of the dia- properly, a horn couples sound energy speaker quite uniformly over the entire phragm to the other. They overlook from high pressure and low velocity range of frequencies which the horn is the fifth item, which is - just as im at its throat to low pressure and high designed to handle. The standard velocity at the mouth. formula for an exponential horn is S Basically, a horn is a tapered tube of some sort with a sound source at the where S is the cross-sectional area at smaller end. The manner in which point x along the axis of the horn; So cross-sectional area increases from throat is the cross-sectional area at the throat to mouth is called the flare; and the ( small end) of the horn; a is the flare, together with throat area and quantity 2.718, the base of natural horn length, determines the operating logarithms; m is the flare constant; and characteristics of any particular horn, x is the distance from the throat along whether used for hi-fi reproduction or the axis. It is more easily explained as calling sheep. a horn in which the cross-sectional area Most theoretical considerations of doubles at equal distances along the horn design assume an infinite horn, and length of the horn. The distance in in this case the flare alone is the con- which this doubling occurs determines trolling factor. Two variables are in- the low frequency limit of the horn's volved: the shape of the flare (that is, impedance -transforming properties, and the formula which regulates the expand- is determined by the flare Fig z. Throat of high -frequency horn. constant. ing cross section) , and the flare con- Low -frequency cutoff can be quite portant: namely, the air between the stant. For those readers who resent this accurately determined with more com- operative face of the diaphragm and sort of simplification, full mathematical plicated formulas, but a good rule of the listener." treatment can be found in Olson's thumb to remember is that a horn which Mr. Voigt found the answer in ex- Elements of Acoustical Engineering or doubles its area every foot cuts off at

24 AUDIOCRAFT MAGAZINE about 60 cps. Similarly, one which reproduced by the bass horn at all. Such and two higher -frequency horns com- doubles every 2 ft. will have a 30 -cps designs are also commonly coiled or bined in one assembly. The middle - cutoff, and a horn whose cross section folded to conserve as much space as pos- frequency horn is mounted inside the doubles every 6 in. will have a lower sible, Fig. 2, and this again is possible center pole of the bass unit's magnet, limit of about 120 cps. Above the cut- only because the lower frequencies are so that the curved speaker cone- serves off frequency thus determined, the load quite insensitive to minor discontinu- as part of the horn flare. The coupling on the speaker will be almost purely ities. Folds and bends do all sorts of chamber and phasing plug show quite resistive. At frequencies below that for clearly. A separate superhigh -frequency Courtesy James B. Lansing Sound, Inc. which it was designed, a horn acts as an horn is mounted at the front of the inductive load - it is as though an ad- unit; all three drivers have completely ditional mass had been attached to the separate electrical and magnetic circuits. driver cone. In some horn designs this A novel tweeter design recently mar- inductive reactance is used to extend keted by James B. Lansing is the Ring the frequency response below the Radiator illustrated in Fig. 4. Instead natural cutoff of the horn, as will be of a circular diaphragm, with its at- explained a little later on. tendant resonance and phasing problems, the sound source is a light ring Courtesy Jensen Mfg. Co. driven by a fairly large voice coil. This annular sound source feeds a sort of doughnut -shaped horn and the whole what is Fig. 4. Driver -horn for extreme highs. thing winds up in virtually a circular mouth. discouraging things to higher frequen- The middle- and high -frequency sec- cies; that is why the reflex configuration tions of the famous Klipschorn are common in PA horns is so seldom used shown in Fig. 5. The squawker horn in high -quality tweeter horns. is made by Klipsch from his own design A properly designed horn not only - the peculiar duckbill shape is espe- raises the efficiency of the speaker sys- cially plotted to give uniform dispersion tem, but the uniform acoustic load it over a 90° angle. The high -frequency provides damps the driver quite heavily, unit mounted in the mouth of the larger and so reduces resonances and distor- horn is the University 4401 tweeter. In tion. As Mr. Voigt puts it, "For life- spite of its modest price, the 4401 com- like reproduction, good transient re- pares with many more pretentious sponse is even more important than the tweeters, and what Klipsch especially Fig. 3. Unitary three-way loudspeaker. far extremes of frequency scale. Damp- likes is that its efficiency corresponds to ing improves a diaphragm's ability to that of the rest of the system. Many The formulas for theoretical response follow transients accurately, and air high-frequency horns are so efficient of an infinite horn apply for a finite loading is an excellent way of providing one, provided that the mouth diameter damping. By using a horn, it is possible Courtesy Altec-Lansing Corp. ( for a circular horn) is at least one to extend downward the frequency third the wave length of the lowest range over which reasonable matching, frequency to be reproduced. This means and therefore air loading, is maintained. a horn mouth almost 10 ft. across for Unfortunately, just 'any old horn' will a 40 -cps horn. No commercial horn - not do, for a bad horn may sound worse type speaker has ever been marketed than the trouble one is trying to mini- in this country with a cutoff frequency mize." lower than 40 cps, and it is easy to see The fact is that it is easier to design why. a bad horn than a good one. Perhaps Before we continue to the more in- the best method of illustrating how teresting considerations of practical horn these considerations of horn design design, there is one more basic problem Courtesy Klipsch that should be mentioned. It would & Associates seem common sense to couple a loudspeaker to a horn simply by designing Fig. 6. A coaxial (2 -way) combination. the horn throat to have the same area that a pad has to be used to balance as the speaker cone, and then screwing the two together. However, higher ef- their output with associated speakers. it rather simple- ficiency can be obtained if the horn Mr. Klipsch considers money amplifier throat is smaller than the driver dia- minded to spend for an with a high damping factor, and throw phragm and this necessitates some sort the benefits of electrical damp- of coupling chamber. Since the distance away all ing by inserting a constant impedance from the horn throat to the source of pad the and the sound is different at various points on between amplifier Fig. 5. Squawker & tweeter horn array. with tone the diaphragm, phasing plugs have been speaker. Regulating brilliance controls does not affect speaker damp- designed to minimize high -frequency apply to good speaker systems is to take ing, but putting a control on the speaker losses in the coupling chamber (Fig. a look at a few commercial horn-type itself upsets the electrical coupling be- 1) . This is mainly a problem in public- systems. amplifier and the speaker address units and horn -type tweeters. tween the system. Low -frequency units are not so criti- High -Frequency Horns In the Klipschorn, both middle- and cal in this respect. A plain box may Fig. 3 is an excellent cutaway photo of employ be 'used as a coupling chamber, since the Jensen G-610 Triaxial speaker, high -frequency units special high frequencies are not meant to be which is actually a cone -type bass driver Continued on page 38

DECEMBER 1956 25 TRANSISTORS in Audio Circuits

by PAUL PENFIELD, JR. IIIa: Junction Transistor Characteristics

THE preceding two installments in ber the electrical properties when For a three -terminal device such as this series stressed the physical they are related to a good know- a transistor, several such plots are pos- nature of the junction transistor, and ledge of transistor action. Finally, discussed a few other types of transis- the abnormalities and unusual charac- tors and semiconductor devices. A phys teristics of transistors are most easily explained by referring to the physical picture of the transistor at work. W But it is necessary also to be familiar with the electrical properties of transistors. This installment deals with the electrical characteristics of common

junction transistors, and the way these VOLTAGE vary under different conditions. I will

VOLTAGE discuss the common curve families in terms of nonlinearities, and maximum NEON LAMP ratings, and then talk about transistor RESISTOR noise and high -frequency response. The Collector Family For any electrical device the most interesting information is usually found Fig. 4. Multi -valued volt-ampere curve. in its volt-ampere characteristic. This is Fig. r. Volt-ampere curve for resistor. a plot of the current in the unit vs. sible. Usually the current into (or out of) one terminal is plotted for chang- ical picture of the transistor, and of ing values of the voltage between that transistor action, is not directly useful terminal and one of the other two, in designing transistor circuits. How- with a number of different fixed con- ever, it is very important in the long ditions of the third terminal. run, for while a designer can get by The most useful family plot like this without this intuitive understanding, he is shown in Fig. 6. Here the collector cannot do his best, and is often at a current I, is plotted against the collector- loss to explain unexpected effects. to -emitter voltage V,a, for a number Furthermore, it is easier to remem- of different values of base current L. VOLTAGE Base current is here called the running parameter. This graph is known as the JUNCTION DIODE ground -emitter collector family. Fig. 6 does not apply to any given transistor; rather, it shows all the char- Fig. 3. Diode curve is unsymmetrical. acteristics of junction transistors as a the voltage across it. With a resistor, class, and indicates clearly the limited for example, a straight line tells the region in which transistors usually oper- VOLTAGE whole story; see Fig. 1. A varistor, a ate. Fig. 7 shows the circuit which junction diode, and a neon light all produced (or could have produced) the require more complicated graphs, as in curve family of Fig. 6. VARISTOR Figs. 2, 3, and 4. Note that the neon First, look at the so-called linear light even has two lines at some volt- region - where the lines of constant ages - indicating lighted and not - base current are roughly horizontal. It lighted conditions. For some devices is here that most people use the tran- such as a capacitor, no volt-ampere plot sistor. Here the distortion is the lowest, is possible; instead, as in Fig. 5, volt- and the amplification the highest. If we Fig. 2. Varistor has a nonlinear curve. age may be charted vs. charge. fix the collector -to -emitter voltage at

26 AUDIOCRAFT MAGAZINE some constant value (as, for example, by in the linear region: the lines of con- voltage end - this time by the cutoff connecting a battery between the col-, stant base current are almost horizontal, current. lector and emitter) and vary the base indicating that the collector current is Remember that a reverse -biased col- current, we find ourselves going straight indeed independent of the collector lector junction does allow a little cur- up and down on the graph, along such voltage to a large degree. rent to flow through it, current that is Lines in the linear region are nearly caused by thermal effects. This cutoff equally spaced and parallel; if the device current depends on the temperature, and were truly linear, they would be exactly only slightly on the junction voltage. equally spaced and parallel. Some dis- Remember further that the transistor, tortion -causing nonlinearities occur even when biased in the normal direction, inside the commonly used "linear" with the base floating, amplifies this region. cutoff current by means of the hook That region to the left of the linear multiplier. area (shown enlarged in Fig. 9) is Now refer to Fig. 6 again, or the known as saturation. Here all the col- enlarged view shown in Fig. 10. Here lector current that can flow is flowing, -77 and a further increase in base current P r -P can increase the collector current very little. It happens in many transistors that 0 the minimum collector voltage for any v60 given collector saturation current is pro- _1 T portional to that saturation current, at Fig. 7. Circuit used for Fig. 6 curves. least approximately. Consequently, the saturation line behaves like a resistance the line of zero base current is at about Fig. 5. Capacitor charge vs. voltage. -hence the saturation characteristics fifty microamperes collector current --- of a junction transistor can be almost that's one microampere cutoff current a line as CD in Fig. 8. If the base completely specified by giving its satu- multiplied by the hook mechanism fifty current varies, say, between points A ration resistance. In Fig. 9 this is about times. and B in Fig. 8, the collector current 20 ohms. As far as the transistor is concerned, will vary also, and considerably more For certain types of nonlinear opera- there is nothing particularly significant than the base current. In this example tions (such as power switching) it is about the value zero for base current. it varies about 49 times as much. This important to have as low a saturation It is possible to make the base current is merely transistor action at work, and resistance as possible, although for nor- reverse a little bit and still remain in- the explanation in Part I of this series mal low -power audio work it doesn't side the linear region. In fact, the base would predict this sort of behavior. much matter. current can go negative as much as the It was remarked before that the value Saturation is the high -current, low - normal cutoff current I,0, at which point of collector voltage had little effect on voltage region. The linear region is the emitter current becomes zero. The the collector current. This holds true limited also on the low -current, high- Continued on page 32

Fig. 6. Volt-ampere curves for collector of grounded -emitter transistor. Fig. 8. Heavy line shows how changing Ib affects i,.

2dµa

20 30 40 50 60 70 V80, VOLTS

DECEMBER 1956 27 Sound-Fanciers Guide

by R. D. DARRELL

TRADITIONALLY, the December library which I have replayed more about wide -range reproduction's quieter installment of most record -review often or with more consistent delight, virtues: that is, the advantages minimum columns is devoted, at least in part, to at any time of the year, than the original distortion and maximum tonal authen- the outstanding new releases of per- version of this LM 1711. ticity hold for comparatively simple tinently "seasonal" music: a tradition The second, dating in disc form from scores, as well as for complex symphonic which has become increasingly irksome last year (Vox vx 25.010) and now orchestrations. Yet probably I've never to maintain in recent years, since copy scheduled for November or December appreciated their full worth as grate- must be prepared before many holiday - tape release by Phonotapes -Sonore, is fully as I do now when, after my orgy scheduled records actually arrive, and just about as different as it could be - with out -of -this -world demonstration by the time that copy appears in print for it is devoted to wholly familiar recordings of last month (and the al- a great many listener-readers are com- tunes (not excluding such pops as most -as -loud but far more confusing pletely fed up with the excessive com- Berlin's White Christmas and Ander- pandemonium of the live Hi-Fi Show mercial exploitation of Christmas in son's Sleighride), played by a nightclub in New York), I turn back to the sound - as well as in almost every pianist with rhythm accompaniment. gentle old favorites above, and then - other way. Moreover, few recordings But that pianist is Georges Feyer, and so as to preserve my contemplative, low- of the appropriate musical materials are he doubles here as a harpsichordist; tension mood - to a batch of new re- technically notable enough to warrant anyone who knows the best of his long leases drawn from what I have long extended discussion in this particular "Echoes" series will need no further found to be the most completely per- column. prompting to investigate, on disc or sonally satisfying of all musical reper- Yet by sheer chance, two of this tories: those stemming from the baroque year's Christmas specials are not only era. already well known (in other forms) Two of these releases (which, al- to me, but are so exceptional in their though not specifically associated with sonic as well as musical appeals that Christmas, are nevertheless eminently it's a joy to commend them to your well suited for relaxed year-end lis- attention - even if you think you never tening contentment) provide new want to hear another carol again, and chapters in the running story on organ even if you steadfastly refuse to counte- recordings which I began some months nance any compromise in technical ago: Vol. 2 of the complete Buxtehude standards. series by Alf Linder ( Westminster WN The first, which has been around 18149) and the six trio -sonatas in since 1952, now is scheduled to reap- Helmut Walcha's complete Bach series pear under the same number (RCA for Deutsche Grammophon (Archive Victor LM 1711) in what I hope is 3013-4) . Each reveals new insights into merely a reprint, for I can't imagine how tape, the present Echoes of Christmas. baroque composers' and organ builders' any re-recording or reprocessing, how- It may not be great musical art (al- fascination with unmixed tone -color ever skillful, could capture any more though I'm not so sure about that, since contrasts, and new testimony to pres- transparently some of the outstanding many a more famous serious artist might ent day engineers' ability to reproduce examples of unaccompanied small -en- learn something about deftness and these often strange and raw sonic semble singing on discs. . The Robert tastefulness from Feyer) , but it cer- palettes in their authentic vividness. Shaw Chorale has made many fine rec- tainly is immense - and immensely They present, too, a special challenge ords, but no other quite approaches the satisfying - fun. Like the Shaw disc, to listeners, for even the most fanatical beautifully restrained yet infectious ex- this offers no apparent problems in re- of hi-fi addicts, who would never dream pressiveness, combined with the charac- production and sounds effective on al- of letting the most delicate triangle teristic Shavian rhythmic precision and most any kind of equipment. But in tinkle or pianissimo timpano tap escape verve, of the Christmas Hymns and both cases, hearing these works on a his alerted ears, will have to develop Carols, Vol. 2. And the conventionality really first-rate system will be a revela- further aural sensibilities if he wishes of the title gives no true index to the tion of timbre purity, transient clean- to discriminate properly among the refreshing choice of materials, which ness, and sonority naturalness, for which subtle tone tints and nuances of these includes (in addition to several old the casual listener on run-of-the-mill performances. favorites, topped by the best perform- playback gear will be quite unprepared. Linder plays the same Varfrukyrka ance of the The Twelve Days of Christ- Indeed it is perhaps recordings like organ in Skänninge, Sweden, first mas you can hear anywhere) many less these, whose music and performances brought to American audiophiles' at- familiar airs of Spanish, French, and keenly sensitize one's whole emotional tention by Carl Weinrich's Bach series, Italian - as well as of English and responsiveness, which in the long run but he is a more lyrical, if less dra- American - origin. They are precious actually may educate and refine one's matically exciting, interpreter, and the additions to the orthodox carol reper- sense of aural discrimination more ef- music here is in marked contrast with tory, and the whole wonderful program fectively than even the most brilliant Bach's monumental masterpieces. Ex- is crowned by what to my mind is ore of sensational showpiece discs and tapes. cept for the bold Toccata and Fugue in of the most magnificent examples of F major, the pieces in the new set repre- "vocal chamber music", Victoria's mot.t, Go For Baroque sent facets of Buxtehude with which O Magnum Mysterium. There is per- I have written before - in the booklet even most specialists may be none too haps no other disc in my permanent for An Adventure in High Fidelity - Continued on page 41

28 AUDIOCRAFT MAGAZINE R00k Reviews

by Richard D. Keller

Transistor Electronics enough - merely to avoid confusion an excellent (and nonmathematical) with the familiar symbol for the point- treatise is given on the nature of sound Arthur W. Lo, Endres, Jakob Richard O. contact transistor except that the and its various aspects in differing Zawels, Fred D. Waldhauer, and Chung - - point -contact type has now virtually environments. This leads to the sec- (bib Cheng; pub. by Prentice Hall, Inc., faded from view and the industry -wide tions (which are among the best in the Englewood Cliffs, N. J.; 521 pages; standard for all transistors is still the available literature) on microphone tech- $12.00. original point -contact symbol. Also, the niques in relation to room and location In this integrated volume on transistor use of acB instead of ß for the acoustics. Full discussions of reverber- theory and its applications, five RCA grounded -emitter forward current gain ation and microphone -directivity pat- authorities have combined their work in causes a bit of confusion when inter- terns and their effects on the over-all an authoritative and highly useful refer- spersed with cem, the standardized mood and clarity of a recording are ence book. It is written for advanced a denoting grounded -base current gain. presented in a lucid and easily under- undergraduate and graduate students in Such small confusions are to be ex- stood manner. electrical engineering and associated pected in a fast-growing field. Mr. Weiler covers the entire gamut fields, but has value as well for the of sound recording. Instrumental re- industrial electronics engineer. Tape Recorders and Tape Re- cordings from solo guitars to full or- The book begins with a fine qualita- cording chestras, voice recording from speeches tive treatment of the physical bases of to whole operatic groups, recordings transistor operation. Concepts of hole Harold D. Weiler; pub. by Radio Maga- made in small acoustically "dead" stu- and electron diffusion, Fermi level en- zine, Inc., Mineola, N. Y.; 190 pages; dios to those made in large auditoriums ergy states and junction potential hills $3.95, Cloth -bound; $2.95, paper- and churches impose individual prob- are clearly developed and explained. bound. lems which he surveys and discusses in Device characteristics and parameters are For the amateur and semiprofessional detail. then presented in the y, z, and h param- recordist this book contains a wealth Not only are live microphone tech - eter systems respectively, with major of practical information. To begin with, Continued on'page 34 emphasis on the now generally accepted h parameter system. Four -terminal network theory is also introduced, together with a complete table of equivalent circuits for each of three possible device connections - the common -base, common -emitter, and common -collector configurations. Especially valuable and informative are the chapters on biasing and stabilization, and low -frequency (audio) operation. These are of particular interest to the audio engineer or specialist; they contain probably the best presentation of the subject now available in book form. Although specific circuit values and transistors are not given, the design information and special considerations for transistor audio applications are unusually well presented. The final half of the book is concerned with high -frequency operation of the transistor in such forms as amplifiers, oscillators, modulators, demodula- tors, and pulse circuits. A good part of this information deals with point -contact transistors which have just about disappeared from the market picture, although the underlying basic theory can, of course, be applied to the newer junction types as well. The junction transistor symbols used throughout the book are rather surprising since they resemble the symbol of a tube with an arrow for a cathode. The reasoning behind this seems logical 270 pounds of plywood, 35o pounds of sand, and the best bass you ever heard!

DECEMBER i956 29 Amplifier Construction the tiny capsules and was useless. A baffle. Wing nuts made finger tight visit to the local quarter store convinced on lock washers are a good fastening of a three-inch Working at the bottom me that a Goodyear product called medium. in the corners, deep chassis, especially Pliobond was probably an adequate ad- High humidity, such as that pro- temper and the can be hard on one's hesive, if not identical with the original. duced by a three-day rain when the insulation of surrounding wires. The I used it, following the original in- home heating plant is not in service, shallower chassis is not possible use of a structions for the disc adhesive, and can inject a tubby sound into the sys- used. However, if vector sockets are found it to be entirely satisfactory. It tem. A 100- or 150 -watt electric bulb the will no longer exist if the corners is therefore recommended to anyone placed near the speaker will restore a of alumi- amplifier is built on sheet who encounters this same problem. those crisp transients. of num or steel, or the proper size Incidentally, the little discs have an Next, inspect the two braided wires, bottom of metal should plate. The sheet additional advantage which is mentioned leading from the speaker terminals to to size and the original be cut the proper neither in the magazine nor by the the cone, for fraying. With the power chassis can be used as a cover. Besides manufacturer; they isolate the receiver on, wiggle them in an effort to detect of working, another advantage is ease from the lead-in, preventing DC or a loose or cold -soldered joint. able to use a steel chassis being cheaper sizable values of AC from getting If the trouble has not yet been un- without having the hole -cutting job that through. If a power line should fall covered and there are no obvious de- steel usually brings. across the antenna, or if the mast should fects in the cone, the fault is probably out the chassis, make When laying become grounded while used with a under the dust cap. If it is in the chokes, paper outlines of transformers, hot-chassis receiver of any sort, the ac- voice coil, it is a job for an expert; can condensers, and tubes, shuffling but, in that case, the speaker is usually them around until you're satisfied. Then inoperative. H. A. Hartley says that measure the outline and buy your the action of the cone will prevent dust chassis. The average chassis flange is from collecting. Moving the cone in just under 1/2 in., so allow this much for and out with the fingers may cause a clearance when laying out. scraping noise, indicating the presence The only disadvantage of this method of foreign material such as a metal is that it is necessary either to have filing After carefully removing the dust all connectors and controls on the top cap with solvent, this foreign matter can of the unit, or to use leads long enough cident will not damage the receiver nor be fished out with a folded piece of to allow opening the unit. burn down the house. On the other Scotch tape. Arthur M. Day hand, a window pane is not likely to Finally, those experimenters making Venice, Calif. deter a lightning bolt that gets past use of AUDIOCRAFT woodworking arti- your arrester. cles should have an extension speaker Lead Harry L. Wynn in the workshop. For this, any cheap FM/TV -In Derry, Pa. speaker for which a replacement cone Other FM addicts may have found, as is readily available will do. On this I did, that the best method of taking First Aid for Loudspeakers they can try all the suggestions made a high -frequency lead-in through an A lot of literature has been written for doping the edges, packing and un- apartment house window is by means about loudspeakers, but, when one goes packing the cabinet with acoustical of Window-Thru lead-in discs, which sour, it's hard to find a step-by-step list- material, and so on. Meanwhile, the were described and recommended in a ing of a few simple things the audio- living-room speaker will remain un- "Tested in the Home" report in the phile can do to restore the instrument to disturbed. January 1955 issue of HIGH FIDELITY service. Many writers simply advise C. A. Robertson Magazine. For those who do not have sending the speaker to an expert. Here Mamaroneck, N. Y. that report, it should be mentioned that are a few suggestions, accumulated over this is a capacitive device in which the years, which may save some reader Bathing Records small aluminum discs are cemented to the loss of a speaker to a repair shop Fingerprints, dust, and grime can be- each side of the window glass to form for several weeks. come so thoroughly hardened in the coupling condensers. Thus, there is no First, to check warping, loosen all the grooves of microgroove records as to need to drill verboten holes, or to bolts or screws securing the speaker defy the cleaning action of dust cloths squeeze the lead-in through metal win- to the baffle. Three -quarter -inch ply- or antistatic devices. Most audiophiles dow frames, which are apt to weaken the wood should not warp, but green fram- have a few recordings in this condition, signal. ing material can pull it out of shape. and hesitate to play them anymore for In preparing to use my discs, however Slight warpage of the speaker frame fear of damaging the reproducer stylus. (two sets; one for FM and one for can cause considerable distortion, and, If these recordings are not mechanically TV) , I found that the glue supplied for this reason, it is not advisable to ruined (if they do not have "hang- by the manufacturer had hardened in fasten the speaker too tightly to the repeat" points or severe scratches), they

30 AUDIOCRAFT MAGAZINE can be salvaged for more hours of en- but for several weeks I was unable to joyable listening. Here's how to go reduce the hum level from the Ferranti NEW, StSEt, ose about it. to my satisfaction. Of course, I at- Prepare a concentrated solution of tended to all routine matters such as Brand-new steel -band and ordinary detergent and lukewarm water proper orientation of the matching Caribbean releases from and wash the record surfaces with a wad transformer, placement of the leads from Cook Laboratories-be the of absorbent cotton. Don't be afraid to the transformer to the arm, a check of first on your block to own bear down on the record surface; cot- the dress of the filament leads in both ton is soft enough so it won't damage the preamplifier and the power am- them! the grooves, and the detergent solution plifier, and adjustment of the hum MUSIC TO AWAKEN THE will not attack the vinyl record material. balance control. Finally, to my jubila- BALLROOM BEAST After washing both sides, rinse the tion, I discovered that connecting a (Brute Force Steel Band of Antigua, B W.I.) record in tepid water. Shake off as lead between the common lug of the (12" LP-$4.98-# 1048 ) many water globules as possible. Place speaker output terminal block and A new record by the hypermelodic gen- the record face down on an absorbent ground (the faceplate screw on the tlemen of the Leeward Islands-an on - cloth. wall receptacle) resulted in significant the-scene recording that proves they're greater than ever. Of course, during the washing and reduction in hum. In my amplifier rinsing process try not to get the record (Heathkit Model W-5), the common PRIZE-WINNING label wet. Even if a few drops of water terminal is connected to the ground bus. KATZENJAMMERS do land on it, no great harm will be This lead, then, provides a low -resist- ("Steer Band With Velvet Gloves") i 12" ) done. Record labels are practically ance path to ground from the amplifier LP-$4.98-# 1047 Dazzling molded into the surface of the record, and, because the pickup lead shield orchestral arrangements, featuring the amazing "humming -bird" style of and they will not pucker or peel off is connected via the preamp to the Percy Thomas, tenor pan by the winners unless soaked to saturation. amplifier ground, for the pickup as well. of the major steelband festival compe- A record thus cleaned has a notice- John E. Turner tition ably lower surface noise; it's easier to Twin Falls, Idaho CASTILIANNE keep clean too. (Maracas Waltz) Norman V. Becker (12" LP-$4.98--#10890) Hollywood, Calif. A sultry jazz waltz version of the Vene- zuelan joropos and manzanares-a pan- orama of equatorial-jazz and dance forms Tape Storage from Belem to Caracas (including the Living, as I do, in a very small city in Girl Pat All -Girl Oil Drum Orchestra) a rural area, it is not possible for me LE JAZZ TRINIDAD to purchase audio equipment locally. (12" LP -84.98-# 10850 ) I'm willing to bet that one couldn't buy Insidious new sounds from Trinidad, fea a reel of tape within a radius of 50 Stylus -and turing Rupert Clemendore and Combo -Record Brush in sophisticated jazz with miles. The point is that audio equip- a pixie beat, Keeping a stylus clean and free of dust vibes 4 drummers, sax, piano. Recorded ment is difficult to come by and it is always pays off in better reproduction stealthily at Port of Spain often necessary to improvise. and longer record life. A stylus brush THE CHAMPION STEEL BANDS For a long time I was unable to can be made easily and inexpensively OF TRINIDAD obtain the metal cans in which reels of from a one -inch camel's-hair brush ( 12" LP-$4.98-# 1046 ) magnetic recording tape should be which can be purchased at most dime Six socko bands from "the birthplace stored. Here's what I did of before I was stores for about 40¢. Cut off the brush steel"-a glorious kaleidoscope of steel able to get these cans. First I wrapped handle at the metal ferrule and you styles and prize-winning performances on the reels a single disc of tape in a plastic wrap, have an excellent stylus -and -record such as Saran wrap, and then in several brush. DANSE CALYPSO layers of foil. aluminum I found that To clean a record, place it on the (12" LP-$4.98-# 1180 ) this type of wrapping preserved the turntable and, while it is turning, hold Johnny Gomez and his Orchestra for tape about as well as metal cans do the brush lightly on the record, working calypso dancing; four great Calypsonians (The Dictator, Lord Cristo, Herbert and, although it doesn't look as neat, from the outside toward the center. The Howard it makes a good substitute wrapping and Small Island Pride) sing their greatest camel's hair is fine enough to clean the numbers An on -the -scene recording when cans are not available. grooves thoroughly. James R. Garrett A bracket to hold the brush can be at your Dealer NOW! New Boston, Ill. made from a piece of brass rod 1vg in. COOK Laboratories, Inc. in diameter. Allow enough on each end Hum Reduction to make "eyes", and then wrap two 101 2nd St., Stamford, Conn. Magnetic pickups, particularly ones with turns around the brush. The bracket a low-level output, are very sensitive to can be attached to a convenient place r stray magnetic fields and the resulting on the phonograph. Get the Complete Catalog hum in the speaker can be annoying. Terry McConnell Cook Laboratories, Inc. The power supply of virtually all high- Petoskey, Mich. 101 Second Street, Stamford, Conn grade amplifiers is so well filtered that Dear COOK 60-cps hum is reduced practically to AUDIO AIDS WANTED Please send the latest COOK Catalog inaudibility. Consequently, any hum and also put my name on the list to That's right - we'll pay $5.00 or receive the COOK publication "Audio output in the speaker can usually be more for any short cut, suggestion, Bucket" attributed to stray magnetic fields in or new idea that may make life easier the vicinity of the pickup. for other AUDIOCRAFT readers, and Name which gets published in our Audio My own unit is equipped with both Aids department. Entries should be Address a GE variable -reluctance unit and a at least 75 words in length, and ad- City Ferranti ribbon pickup. dressed to Audio Aids editor. No The no -signal State output from the GE pickup was good, limit on the number of entries. L J DECEMBER T956 31 TRANSISTORS voltage somewhat lower will be specified as the maximum operating voltage Continued from page 27 for the transistor. Since transistor action ceases in the breakdown region, transis- collector current then is equal to I,,,, a tors are not normally operated here. value below which it cannot go unless However, it is not impossible that use the collector voltage is reduced to a could be made of it in some applications. The linear region of the transistor is limited on the high collector current o side by a crowding of the lines of constant base current. Fig. 6 shows clearly how the lines crowd and become less horizontal at higher currents. The o crowding of the lines indicates a loss Report from the of gain; eventually, if we go out far LABORATORY a., enough without burning out the tran- a power loss will occur, instead M sistor, ?ke Audio League Report* of a power gain. In looking back at Fig. 6 again, we Acoustic Output5at CPS 30 n can see that the linear region is bounded on all four sides by nonlinearities. On AR -1W N the bottom and the left, there are the 7 5w The League's ref - 75 db erence standard relatively sharp transitions to cutoff and saturation. On the right, the junction breaks down and passes excessive cur- 7.8w 15" speaker V e rent; on the top, there is a gradual 75 db system O e1 0.2 0.3 0.4 OS Os 0.7 V5C. VOLTS lowering of gain indicated by the alpha Fig. 9. The saturation region enlarged. crowding. The region in the middle is of most use to us in designing transis- 18w 12" speaker "ET very low value. In this case, Ieo is equal 75 db system J. tor circuits; however, it is essential to to one microampere. know the characteristics of the other Right from a collector current of I, on up, the transistor is in the linear 2 5w 15" speaker ry region even when the base current is 3.µa 75 db system - slightly negative. The change from the linear region to the cutoff region is very abrupt - even more abrupt than 'Vo No. 9, Oct., '55. Authorized quotation #28. the change into saturation. Ó For the comp ete technical and subjective report on 2µe the AR -I consult Vol. 1 No. 11, The Audio League The linear region is limited on the Report, Pleasantville, N. Y. right-hand side of Fig. 6, at high collector voltages, by a breakdown phe- Report from the nomenon. It is natural, after all, that the material cannot withstand very high 8 WORLD OF MUSIC Ibatµ voltages without breaking down. Break- down occurs when electrons or holes a passing through the collector junction get speeded up fast enough so that they knock covalent bonds apart, forming 2 IbsO new current carriers. When each car- rier, on the average, knocks one covalent bond apart, then a sort of "chain reaction" occurs and the current becomes

very high; it is limited mainly by the 0 i O 10 20 bulk resistance of the germanium itself. Vec, VOLTS The Aeolian -Skinner Organ Co. uses an AR The junction no longer acts as a rec- woofer (with a Janssen electrostatic tweeter) Fig. to. Expanded view of cutoff region. in their sound studio. Joseph S. Whiteford, vice- tifier, and transistor action stops. pres., writes us: Formerly this breakdown phenome- regions, both to learn to exploit them "Your AR -1W speaker has been of non was called the Zener effect, be- well, and to learn to avoid them when inestimable value in the production of our re- cause of similarities thought to exist they are not wanted. cording series 'The King of Instruments'. No between semiconductors and dielectrics, other system 1 have ever heard does justice to Maximum Ratings the intent of our recordings. Your speaker, with whose breakdown characteristics are dif- its even bass line and lack of distortion, has so ferent but were first explained by Zener. At first glance the preceding material closely approached 'the truth' that it validates However, the simple breakdown "chain might appear as if the transistor could itself immediately to those who are concerned reaction" mentioned earlier was found be operated anywhere in the linear with musical values." to be correct. The name Zener seems region. There are certain maximum AR speaker systems (2 -way, or woof- ratings, however, which should er -only) are priced from $132 to $185. Cabinet to have stuck, though, and the break- not be size 14" x 11%" x 25"; suggested driving power down voltage is still called the Zener exceeded in normal operation. These 30 watts or more. Illustrated brochure on voltage. are usually set by the manufacturer a request. The voltage at which breakdown oc- little on the conservative side, and oper- ACOUSTIC RESEARCH, INC, curs can to some extent be determined ation within maximum ratings will vir- 24 Thorndike St., Cambridge 41, Mass. by the manufacturer, and normally a tually neyer burn out a transistor.

32 AUDIOCRAFT MAGAZINE The three maximum ratings - volt- out. Because it is virtually impossible age, current, and power -are deter- to prevent excessive dissipation above mined differently, and for different the breakdown voltage, this effectively reasons. They are not meant to be places an upper limit, or rating, on the applied simultaneously; that is, the collector junction voltage. maximum rated voltage times the max- Normally the voltage from base to imum rated current is usually far greater emitter in a transistor stage will be than the maximum rated power dis- small compared to the voltage rating sipation. for the collector junction, so the col- A power dissipation rating is specified lector -to -base voltage rating can be by the manufacturer from a knowledge thought of as applying equally well The AR -1 acoustic suspension* speaker of the damage excessive temperature from collector to emitter. system is now widely recognized as reproducing does to the transistor. In power transis- A third rating given by transistor the cleanest, most extended, and most uniform tors this is a subject of paramount im- manufacturers is maximum collector cur- bass at the present state of the art. It is em-

portance, and will be covered in a rent or maximum emitter current. Since ployed as a reference testing standard, as a later installment. For low -power tran- the two are so nearly the same, it makes broadcast and recording studio monitor, as an sistors, fortunately, the problem is less little difference to which the rating acoustical laboratory test instrument, and in severe. applies. Germanium transistors cannot in High current in a transistor will not, thousands of music lovers' homes. general withstand temperatures higher as such, do any harm. But at high cur- The AR -2, our second model, is a two-way than about 90° C. without suffering rents the gain begins to drop off, and speaker system (10 in. acoustic suspension at least temporary damage, so care must the linearity decreases. Furthermore, at woofer and newly developed tweeter assembly), be taken to keep the power dissipation higher currents it becomes very dif- in a cabinet slightly smaller than that of the within the transistor low enough that ficult to stay within the power rating. AR-1-131/z"x24"x113/s". It is suitable for use this temperature is not exceeded. Silicon Because of these factors, manufacturers with any high quality amplifier which supplies units are better in this respect, and some frequently specify a maximum current. 10 or more clean watts over the entire audio compound semiconductors will produce While it is well to stay within this transistors considerably more tolerant of rating, experienced circuit designers range. heating. often disregard it altogether, and form The manufacturer states as a rating their own judgment as to the maximum the maximum permissible peak power safe current, on the basis of the opera- dissipation. If the transistor is to oper- tion of the particular circuit they are ate in an ambient temperature higher using at the time. But since deter- than normal, say in the hot sun, then mining ratings is a very tricky business, it cannot lose heat as rapidly, and must requiring experience and judgment, the be operated at a reduced dissipation. A beginner is advised to stay within the safe rule of thumb for germanium is to manufacturer's stated rating. reduce the power rating by 10% for Fig. 11 shows the permissible region The price of the AR -2 in hardwood veneer each 10° F. ambient above normal 70° of operation. This is defined by the is $96.00, compared to the AR -l's $185.00. F. temperature. This temperature de - maximum voltage ( here 50 volts) , the rating is fundamental to the operation maximum power rating (50 mw) and Nevertheless we invite you to judge it directly, of power transistors, but even for low - the maximum current rating (5 ma in at your sound dealer's, against conventional power units it is important. our example) . Note that this permissi- bass -reflex or horn systems. The design sacri- The maximum collector -to -base volt- ble region does not correspond exactly fices in the AR -2, comparatively small, have age is specified by the manufacturer with the linear region discussed before; mainly to do with giving up some of the AR -1's from a 12 knowledge of the breakdown indeed, Fig. shows Fig. 6 and Fig. performance in the nether low-frequency re- voltage for the junction. This break- 11 superimposed. Because of power gions, performance which is most costly to come down increases the current to several limitations, not all the linear region is by. The AR -2 can radiate a clean, relatively full times its normal value, and accordingly available for use. increases the power dissipation exces- signal at 30 cycles. sively. Excess voltage on a junction in Part Illb, next issue, will discuss The AR -2 speaker was designed as the itself does no harm, but once it breaks other curve families, curve variations, standard for medium -cost high fidelity systems. down, much power will be dissipated, transistor noise characteristics, and tests have shown it to be so far ahead of its high -frequency operation. Our and the transistor will heat up and burn price class that we think it will come to be Figs. xi and is Maximum rating boundaries parts of Fig. 6 within the ratings. regarded as such a standard within its first year.

MAXIMUM CURRENT e 5 1114 100

MAXIMUM POWER 50µa M a50MILLUWATTS Literature, including complete performance specifications, available on request from:

MAXIMUM ACOUSTIC RESEARCH, INC. VOLTAGE .50 VOLTS Ibc0 24 Thorndike St., Cambridge 41, Mass. 10 20 30 40 50 10 20 30 40 50 V VOLTS Vec,VOLTS Pat. pending and copr., Acoustic Research, Inc.

DECEMBER z956 33 TRACKING ERROR The graphical method of analysis about 40,000 cu. ft., and is roughly outlined above is very useful for evalu- cylindrickl in shape. A serpentine - Continued from page 20 ating existing arms and comparing curved brick inner wall and an in- their performance, but the trial -and - verted -cone ceiling serve to diffuse re- and this is indeed the optimum solu- error approach to the optimum is rather flected sound, so that there are no im- tion. tedious. The conditions for optimum portant focal points. Absorptive ma- There is very little variation in the design and for best placement of a non - terial consists of about 300 sq. ft. of outer radii of records of the same nomi- optimum arm are easily obtained with glass fiber behind brickwork grilles. nal size, and the results are not very simple mathematics. Reverberation time is 2.5 to 3 seconds sensitive to it. The average value of for lower frequencies, 3 seconds at R2 for a number of records in the author's In the second and concluding part middle -range frequencies, and 1.5 sec- collection is 5.7o in. for 12 -in. and 4.74 of this article, the author develops onds at 4,000 cps. Each building has for so -in. records. The inner radius simple formulas and charts showing a striking organ designed by Walter depends on the length of the selection optimum offset angle and overhang for any given arm length, and gives Holtkamp. and the groove spacing. The author's examples of compromise adjustments. Such characteristics are ideal for re- collection of LP's seems to have only cording purposes, producing crisp yet one case with R1 less than 2.49 in. It massive sound with phenomenal defini- will be noted that ca/R increases very MIT tion. Unicorn Records has taken ad- rapidly for decreasing R, and passes vantage of this already in a series of through zero at a radius not much Continued from page 22 six Music at MIT releases: The Modern larger than R,. It is prudent therefore Age of Brass (UNLP 1031), four con- to design for the smallest R1 likely to be The most important acoustical treat- temporary chamber compositions for encountered. The value R1 = 2.40 in. ment, however, is the cushioned seats brass, performed by Roger Voisin and will be used in numerical examples in the auditorium. Reverberation time his Brass Ensemble; Concertos for Organ below. That is for so- or 12 -inch is quite small at low frequencies - 2.2 and Orchestra (UNLP 1032), four 33.3 -rpm records. 78 -rpm records are seconds at 100 cps - decreasing to 1.6 Handel concertos from Op. 4 and 7, recorded down to R= 1.875 in., but with Lawrence Moe, organist, and Klaus if the arm is nearly optimum for LP's Liepmann conducting the Unicorn Con- the distortion on inner grooves of a 78 cert Orchestra; Beethoven Sonatas for will be comparable to that on inner Piano, Op. 109 and 110 (UNLP 1033), grooves of an LP, because of the inverse Op. 57 and 111 (UNLP 1034) ; Liszt dependence of distortion on record Sonata in B Minor, Op. 178, and Béné- rpm as shown in Eqn. (is). Since seconds at middle frequencies and 1.4 diction de Dieu dans la Solitude from 7833.3 = 2.35, a distortion index 2.35 seconds at 4,000 cps. Op. 173 (UNLP 1035); and Haydn times greater can be tolerated at 78 rpm. The MIT Chapel is much smaller, Sonatas for Piano, Nos. 32, 46, 50, and 51 (UNLP 1036). All the piano works are performed by Ernst Levy, a noted composer -pianist. A single microphone, suspended 20 ft. in front of the performers and 20 IN ? ft. above the stage, was used for the WANT THE FINEST HI-FI brass recording. One microphone in the organ loft and another 10 ft. above of information about actual Are you looking for an unbiased source the chapel floor were used for the equipment performance - facts not claims? In the AUDIO LEAGUE REPORT you will find factual technical data, true curves, actual figures Handel concertos. For the piano works on measured performance, and candid opinions. a single microphone was hung 10 ft. above the piano. Recording and disc of price If you want the best in high fidelity regardless mastering was done by Peter Bartók, If you want to make every dollar you spend count long respected in the industry for his If you want improved performance excellent work in both fields. These If you have a limited hi-fi budget records have all been released except for 1036, which is scheduled for Feb- You need the AUDIO LEAGUE REPORT - based on complete labora- ruary; all should be heard for their evaluations. Test methods and procedures tory tests and panel listening unique technical quality as well as the are clearly stated. Here, in the most quoted source of unbiased information about hi-fi equipment performance, you will find the facts you fine performances. need to make decisions BEFORE you buy. Know all the facts. Do as the experts do, subscribe to BOOK REVIEWS THE AUDIO LEAGUE REPORT Continued from page 29 P. 0. Box 363C Mt. Vernon, New York niques covered, but also techniques for Enclosed find remittance mentioned, please send to re-recording and actually improving the sound from old shellac and cracked Address Name records, and for building libraries of Free folder about the Audio League Report music from AM and FM radio broad- $r for two recent issues including a cumulative index casts. Several chapters of suggestions $4 for twelve issues Start with current issue for improving slide and home-movie $7 for tweny-four issues Start with summary issue (Vol. $9 for thirty-six issues i, No. 12) shows with the addition of appropriate Send all 16 back issues musical backgrounds and commentary, and a chapter on producing realistic sound effects, will be of special interest to photographers. The importance of

34 AUDIOCRAFT MAGAZINE having continuous "background noise" editing jigs. Tapes too wide will tend the stickiness which produces high-fre- in edited tape and of the overlap of to stick in precision -machined tape quency flutter or squealing on recorder sound effects for true naturalness are guides or on heads which have slight heads. Low friction is obtained by a well emphasized. shoulders worn into them by standard - very smooth oxide surface or an added All in all, modest as it is in appear- width tapes. dry lubricant, or a combination of both. ance, this book is highly recommended The ideal tape also has no tendency This is a long list of exacting re- to all who enjoy the art and science to cup, curl, or twist when winding. quirements, and the majority of them of capturing the sounds around them. These are defects that develop after the are unmeasurable by the user. There tape has been used for a while; they are, however, several tests that a re- Maintaining Hi-Fi Equipment contribute to poor handling at high cordist can make to determine the over- Joseph Marshall; pub. by Gernsback speeds and, in extreme cases, to poor all quality of a new brand of tape. Library, Inc., New York; 224 pages; head contact. First, clean the tape recorder's tape No. 58; $5.00, hard cover; $2.90, soft Tape should not shed its coating, guides, heads, and capstan thoroughly cover. binder, or lubricant. Peeling of the with alcohol. Then thread the new reel run it For electronics technicians, repairmen, magnetic coating is obviously an unfor- of tape on the recorder and forward mode all and audio enthusiasts in general, this givable flaw, but this has fortunately through in the fast been eliminated by modern bonding the way to the end of the reel. Note volume is a veritable audio bible. It of particles smoothly from the reel was published in the middle of 1956 processes. Shedding oxide whether it pulls layers seem to be sticking and much of the contents must have or formulation additives will tend to or whether its of the heads together. between layers of been written at the last minute, for it cause fouling (with drop Stickiness out or loss of highs) and dirty tape a new reel of tape may mean that its is truly up-to-date. edges are not smoothly cut or that its The very latest commerical high- coating binder or lubricant is sticky. fidelity circuits, such as the Unity - Either may endanger future recordings Coupled Horizon (National) and the by introducing irregular speed varia- Circlotron (Electro -Voice) are ex- tions. plained and analyzed, as well as the After the tape has been wound on Baxendall negative feedback tone -con- the takeup reel, note how evenly it has trol circuit and several systems for vari- guides, necessitating frequent cleaning wound. If the tape wandered randomly able -damping control. and possibly spoiling valuable record- from side to side, it may be the fault of There is a handy topical division for ings. the recorder. But, if the recorder usually using the book as a reference for all Finally, the ideal tape is frictionless. winds evenly on fast forward, and the sorts of general and specific troubles This is clearly the most idealistic re- test tape did not, it is a sign that the in high-fidelity systems. At the begin- quirement of the lot, but the ultimate tape may be unevenly cut. Also, a ning, high-fidelity standards and ter- aim remains. A low coefficient of fric- minology are presented, followed by an tion reduces head wear and minimizes Continued on next page excellent treatise on types of test instruments and their preferred specifications for adequate checking and maintenance of high-fidelity equipment. The best of the test records, with explana- 1IW ITyOURSELPl tions for their use in checking such conditions as proper equalization and distortion, are listed. QUALITYdJ.1.i:ì The heart of the book deals with distortion in all its many forms, and how ig F/Pu/fl' to diagnose and eliminate it. Proper techniques for balancing push-pull stages, obtaining feedback stabilization, using decoupling networks, and match- CRYS7,4! 9/091//1/te Al ing speakers to enclosures are among the many subjects thoroughly covered. In addition, diagnosing and locating hum; eliminating ground loops; testing Itrif for stylus distortion, phonograph -arm friction and turntable rumble and wow; NO POWER REQUIREMENTS and minimizing distortion in AM and SELECTIVITY (20 KC) LOW FM amplifiers, limiters, and detectors COST NO NOISE LIFETIME may be added to the list. TROUBLE FREE OPERATION There is so much valuable practical SENSITIVITY GAIN CONTROL information in this well indexed work NO.565 SMALL SIZE 4"x7"x31/2" DEEP that it should be at the finger tips of VERNIER DIAL NOTHING TO The Miller No. 565 Tuner Kit is the result of everyone who enjoys building or im- CAUSE DISTORTION FREQ. masterful engineering and careful planning. Pre- 540 KC -1700 KC proving home sound systems. viously sold only as a factory assembled.unit the tuner has received overwhelming acceptance by the The No. 565 tuner kit is fully guaranteed. most critical audophiles, and is far superior to all Buy with confidence from your Radio and other such tuner kits. Only recently have materials TV Parts Distributor. It is one of the TAPE NEWS become available which make possible the con- lowest priced quality tuner kits on the struction of extremely high "Q" coils. Coils used market. Continued from page 14 in our tuner have a "Q" in the order of 600. Net Price $14.70 Assembly and wiring of this is length and from reel to reel. Tapes tuner not difficult. Step by step instructions with exploded views, J. W. MILLER COMPANY that are too narrow will tend to ride pictures and circuit diagrams are supplied with up and down on the heads, and will each kit. 5917 S. MAIN ST., LOS ANGELES 3, CALIF. not work properly with certain types of Canadian Representative: Atlas Radio Corporation, Ltd. 50 Wingold Ave. Toronto 10, Ont., Canada

DECEMBER 1956 35 Assemble Your Own TAPE NEWS occurred and then re-record through that spot. If the same change occurs at the Continued from preceding page same spot, the tape is the offender. Remove the tape from the transport tendency for the tape to wind in bands, mechanism, and examine the heads and HIGH-FIDELITY with alternate bands lying firmly against guides for deposits of coating or binder. the upper and lower flanges of the reel, If this has accumulated to any degree SPEAKER SYSTEM suggests twists or crooked cuts within on the polished surfaces of the heads, the length of the tape. These are minor and if it was found that the tape shed matters as far as the home. recordist is when winding and rewinding (as de- concerned, but where tapes are to be termined previously) , the tape coating used for commercial purposes it is best is poorly bonded. Deposition of a to avoid those brands which wind un- noticeable coating with a single play evenly. indicates an intolerable amount of Now rewind the tape onto the shedding, particularly if the accumula- feed reel, noting again how it unwinds tions have lodged on the active surfaces from the takeup reel. If there is still of the heads. Small accumulations to a tendency for layers to stick together, one side of the head gaps are to be the tape may be expected to give serious expected after several plays, but de- trouble in this respect, and should not position on the gaps is fatal to quality be used if dependability is important. recording. It's Easy and Inexpensive After rewinding, carefully examine Now take another tape of the same to "DO IT YOURSELF" all the surfaces that the tape came in variety as the first sample but chosen contact with while traveling. There from a different production batch. (One ASSEMBLE THE ELECTRO -VOICE will probably be small amounts of resi- store should EMPIRE Low -Boy KD 5 SPEAKER purchased from a different due left from the tape, but if there is CABINET. Kit contains everything fill this requirement.) Using the same you need-precut panels and cleats, enough to form large bunches that can volume settings as before, run off about glue, screws, and easy -to -follow di- be chipped off with the fingernail, the a minute of the 400 -cps tone onto the rections. It's yours for $51- tape probably has too great a tendency second sample, and play it back. Its Build your own, if you prefer. Buy to lose its coating, binder, or lubricant. output level should be within 2 db of just the illustrated construction that of the first sample if the tape is book-$1.00-get your materials to be used for professional applications, local from suppliers. or within 4 db if nonpro use is en- Give your completed cabinet a furniture finish-cherry, cordovan visioned. mahogany, walnut, golden oak, Before making up your mind about this, Now comes the most critical test of fruitwood or ebony. Finishing though, wait until it has been tested in the new tape; its performance test. Re- to 20 db kits, $5. the record mode, as follows. duce the record level about Improve Your Speaker System Thread the tape again, and feed a below normal recording level, and One Economical Step at a Time continuous 400 -cps tone from an os- record a series of test tones at, say, cillator into the recorder at normal 1,000, 30, 50, 70, 100, 500, 2,000, FOLLOW THE SENSIBLE record level (zero db on recorders hav- 5,000, 8,000, 10,000, and 15,000 cps. ELECTRO-VOICE BUILDING Thirty seconds duration will be plenty ing a db level indicator) , and record BLOCK PLAN. Start with an for each tone.' Rewind the tape, set Electro -Voice SP15B co- through the entire length of the tape. axial full -range speaker. When the end of the reel approaches, the playback level to give a mid -scale Just $43 net. note the exact volume control setting reading at 1,000 cps on the voltmeter, For those silky highs, add and turn the record volume all the way and then play back all the tones, noting E -V Model T35B VHF the readings obtained. For the time driver AT37 level control down before stopping the recorder. and Model X36 crossover. (Failure to turn down the volume first being, it doesn't matter whether the For added mid -range re- may magnetize the record head.) Re- response seems to deviate all over the sponse, install Model T10A 024 wind the tape, set the volume control place; the purpose of this test is to H F driver with M odel AT37 check the variability of the tape being level control and Model at its original setting, and connect a X825 crossover. sensitive AC voltmeter (0 -5 -volt range) tested. Complete your three-way to the output of the recorder. Then play When all readings have been noted by adding speaker system the tape and observe the output reading as accurately as possible, remove that these components to your reel of tape and repeat the frequency - to from one end of the tape to the other.' basic speaker and thrill test reels of a magnificent 3 -way system. Observed fluctuations should not ex- response on several other identical tape, choosing if possible tapes the Difference ceed 1 db in either direction if the Hear from other production batches. The re- SEE YOUR ELECTRO -VOICE tape is intended for professional ap- sults should not vary by more than 3 DEALER TODAY. Dial the plications; otherwise, a 2 -db variation db at the highest frequency for which E -V Speaker SYSTEMS is permissible. Larger fluctuations may SELECTOR and hear the is its indicate either that the oxide coating the recorder rated in published improvement as you specifications. If there are wide dif- switch from a single speak- lacks homogeneity or is of varying er to a multi -speaker thickness, or that the recorder's bias ferences between them (of, say 6 db at the high -frequency it is fairly system. supply is poorly regulated. To check limit), safe to assume that the uniformity is 211-8612 for the latter possibility, try the same Write for Bulletin inadequately controlled. test on some other brands of tape, or When running ® put a grease pencil mark on the test aIf the recorder utilizes a separate playback head for monitoring from the tape while recording, Zlecey01Cg, tape at one spot where a large change input/output response comparisons can be made ELECTRO -VOICE, INC. BUCHANAN, MICHIGAN while recording, by flipping back and forth from 10n a recorder having an A -B switch which com- A to B nn the output selector switch and reading Canada: E -V of Canada Ltd, 1908 Avenue Road, pares input to the tape and output from a sepa- directly the db response deviations. For two -headed Toronto, Ontario rate playback head, variations in output can be tape recorders, a short pause introduced between Export: 13 East 40th Street, New York 16, U.S.A, observed while recording, thus obviating the need the tones will aid in identifying them during play- Cables: ARLAB for playing the tape through a second time. back.

36 AUDIOCRAFT MAGAZINE these tests make sure that all the samples bitious the recorder, the less impor- used are specifically identified by the tant become most of the idealized re- manufacturer as the same type. Many quirements that were listed, and that variations in oxide formulation exist the most important thing in this case is between different types of the same to find the brand of tape which gives brand of tape, and these differences the closest replica of the original sound must be considered when making direct on that recorder. It should also be comparisons. emphasized that the foregoing discus- This about completes the quality and sion of magnetic characteristics pertains uniformity tests on the tape itself. The mostly to the slower tape speeds, 7.5 next step consists of checking out the and 3.75 ips. The effects of magnetic tape's performance on the recorder it differences between tapes decrease sig- is to be used with. Since, as it was nificantly at 15 ips and practically dis- pointed out earlier, the suitability of appear at 30 ips. It is thus possible a tape for a recorder will depend to obtain optimum results from practi- largely upon whether the latter has a cally any brand of tape on a recorder variable bias adjustment, it will be operating at 15 ips without making more convenient for us to consider any adjustments to suit specific brands. separately the two types of recorder. This interchangeability does not, how- The professional, recorder, with vari- ever, exist at slower speeds, so most able bias, can be matched to any tape. of us have to match our tapes to our When a new tape is being tested, the recorders, or vice versa. bias (and equalization, if adjustable) should be adjusted for that tape, ac- GROUNDED EAR cording to the recorder's instructions. Then the instructions should be fol- Continued from page 5 lowed in carrying out the frequency - response test on the tape. Unless the this dilemma points out that we still tape is unusually bad (or the recorder have a long way to go before we solve is out of order) its high -frequency the problem of reproduction of music response should fall well within pub- in the home with sufficient success to lished specs at the test speed. It is also satisfy all listeners. with the a good idea at this time to rig up some form of comparator that will Screen Feedback Amperex® allow you to flip from the playback I'm afraid I gave my readers a bad of the tape to the output from the test steer when, in the September issue, I RECTIFIER oscillator, so that an immediate A -B suggested the use of older -type output GZ34 comparison can be made between the transformers with 10% tertiary wind- A LOW-IMPEDANCE, INDIRECTLY HEATED, FULL -WAVE RECTIFIER original and the recording for an audi- ings for screen feedback. Though I WITH 250 MA OUTPUT CAPACITY ble distortion check. Note particularly have not yet received complaints, I am how the tape sounds when reproducing keeping my fingers crossed. It is pos- The unique AMPEREX GZ34 replaces without circuit changes, in the the 30 -cps recorded tone, because some sible that some of these old trans- majority of amplifier circuits, an brands of tape introduce serious modula- formers, or cheap transformers with entire line of popular, heavy-duty 5-volt tion noise (an annoying hiss that varies such windings, may work. But David rectifiers-5U4G, 5V4G, 5T4, etc. with the signal) at low frequencies. Hafler (of the Dyna Company) rushed - with the following benefits: Assuming that the tape does not intro- me a note of caution. Although so far Better voltage regulation due to duce any serious response aberrations there has been very little work on lowered power supply impedance; or undue distortion (some of the latter this scheme, his experience indicates Higher power supply output voltage for more power; is inevitable) , the choice of tape for the that it is probable that the use of a Added filter condenser protection recorder with variable bias will depend transformer not specifically designed due to reduced ripple; mainly on how closely the tape measures for screen feedback will produce a Cooler operation due to lower up to the list of ideal physical require- multivibrator oscillator instead of a voltage drop; ments enumerated earlier. feedback amplifier. If there is capaci- Protection of costly power output tubes through delayed warm-up. With the nonvariable-bias recorder, tive transfer between plate and screen however, the differences in bias require- sections of the transformer, the circuit ments for different tapes can be used will oscillate. Mr. Hafler has had to to serve the function of the lacking work out a new method of winding OTHER Amperex TUBES FOR bias control; if the bias can't be matched transformers to balance and cancel out HIGH-FIDELITY AUDIO APPLICATIONS: the to tape, the tape can be matched capacitive transfer of signals in his EL84/6805 9 -pin power pentode; 17 W PP to the bias. The procedure here is fairly Dyna A-440 transformers. May I cau- 6CA7/EL34 High -power pentode; 100 W PP self-evident; try several brands of tape tion readers, then, not to invest any EF86/6267 Low -noise high -p. pentode on the recorder until a few are found money in trying this idea, and to be ECC81/12ÁT7 Low -noise medium-µ dual triode which give ECC82/12AÚ7 Low -noise low-µ dual triode the best reproduction when prepared for trouble. To those who EC683/12AX7 Low -noise high-µ dual triode their playback is compared directly with may have tried it and run into trouble, EZ80/6V4 9 -pin rectifier; cathode; 90 ma. the original. Recording part of a record my apologies. I can suggest, as a pos- EZ81/6CA4 9 -pin rectifier; cathode; 150 ma. onto a sample of tape will provide the sible way of salvaging the situation, At -All Leading Electronic ideal comparison basis; once the closest using the tertiary for feedback to the Parts Distributors match has been established, that is the cathodes of 6CA7's. As pentodes these time to start considering the tape in tubes have enough sensitivity so that Amperex MI:MU_ terms of the physical requirements. the increase in driving voltage should It should be remembered at least not cause any difficulty, while the cath- ELECTRONIC CORP. - 230 Duffy Ave., Hicksville, Long Island, N.Y. as an afterthought - that the less am- ode feedback will be of real benefit.

DECEMBER i956 37 LOUDSPEAKERS working is that for a given response curve the volume can be greatly reduced, Continued from page 25 for the sound expands into a quarter or eighth sphere instead of into a nomi- dispersion. Another familiar method nal hemisphere." of distributing treble tones is the multi - Realizing that many people do not cellular horn. The impressive Altec have an available corner for their Lansing 604C Duplex speaker (Fig. speaker systems, some manufacturers 6) uses an array of six identical high - advertise horn -type enclosures with frequency horns all driven from a single diaphragm. The mouths of these horns Courtesy Electro -Voice, Inc. are spread out in a fan -shaped arrangement which spreads out the high frequencies. Bass Horns Where treble horns demand close tolerances and delicate workmanship, the biggest drawback to the use of horn coupling for bass frequencies is sheer

Courtesy Klipsch & Associates

the superb new HF -50K POWER AMPLIFIER KIT Fig. 8. The Patrician four-way system. from "built-in" corners which can be placed anywhere. But the advantages of corner location for frequencies no lower than 60 cps requires intersecting surfaces extending at least 5 ft. in all three di- YOU ASSEMBLE IT rections from the speaker, and it is difficult to imagine how a structure this YOURSELF AND SAVE $100: size can be built into a small cabinet. In this country the progenitor of most good corner horn designs is the Klipschorn, by Paul W. Klipsch. Al- If you know how to solder two wires though a trihedrally symmetrical design together, you can now enjoy match- (a sort of pyramidlike affair) had been less amplifier performance -50 of the cleanest watts you've ever heard-for previously described by Sandemann, and the price of an ordinary 20 -watt unit! Weil had done work on corner units, Words can only feebly suggest the Klipsch was convinced that he could breath -taking realism of sound pro- design a corner -loaded bass horn which duced by the REGENCY HF-50K. There is plenty of reserve power to handle didn't occupy so much floor space. You the increased dynamic range of pres- Fig. 7. Inner partitions of Klipschorn. may (or may not) be able to follow ent day program sources and to drive low efficiency, wide range speakers. size. The only satisfactory method of Courtesy James B. Lansing Sound, Inc. High stability and low phase shift retaining fully effective horn loading to prevent bounce or flutter when amplifier is pulsed. Frequency response: reasonably low frequencies, without ±0.2 db, 20 to 20,000 cps. IM and building another room on the house, is harmonic distortion: less than 1 % at to take advantage of corner placement 50 watts. Damping factor: 15. for the speaker system. Any other at- The HF -50K is easy on the eyes, too. Striking black and gold exterior tempt to lessen the mouth area will provides "show piece" styling that inevitably result in tuned column effects makes cabinet mounting a needless due to mouth reflections at low fre- extravagance. quencies. Putting the unit together is an entertaining 4 -hour job. No shock Although corner horns have become hazard. Easy to follow directions popular only in the last decade, they make every step crystal clear. are not new. P. G. A. H. Voigt re- Compare the HF -50K specs with calls, "Corner horns go back to the early those of any other amplifier; then compare the price and see if you days of the cylinder phonograph. I don't agree that this REGENCY Kit is used the principle in 1934, and at the truly the amplifier buy of a lifetime annual Radio Exhibition in Britain that Fig. 9. Harts field two-way horn speaker. ... only $7430 complete! See it at year, the corner horn exhibited by my your distributor, or write: company was the only one at the show. the horn path from the cutaway view In the years since then, the advantages in Fig. 7. The driver faces forward REGENCY Division, I.D.E.A., Inc. of combining corner operation and horn and is joined to the horn through a loading have been fully recognized, and small coupling chamber. The horn Dept. G 7900 Pendleton Pike many famous designs now use the tech- splits vertically, folds around the speaker INDIANAPOLIS 26, IND. nique. The special advantage of corner chamber, reunites, splits laterally, and

38 AUDIOCRAFT MAGAZINE emerges in the final section formed Audible fundamental tones are therefore between the sides of the cabinet and reproduced down to 30 or 35 cps, even AcOu sti - the room walls. though horn loading is lost for all It may come as a surprise that the practical purposes half an octave above magic Klipschorn, long lauded as the ultimate this frequency. in reproduction of deep bass notes, has Jensen employs a similar idea except that, instead of using acoustic capaci- REFLE SLOT tance, the compliance of the cone sus- AIR MASS FFECTIVE pension is used to resonate with the FLOW CUTOFF mass characteristic of the horn. In the Klipschorn, the bass driver must have a suspension resonance much lower than the horn cutoff while in Jensen's "reactance -annulling" design, a cone resonance higher than horn cutoff is employed. We have described the Klipschorn at some length because almost every other Fig. ro. Simple rear -loading bass horn. corner horn manufactured is based on a low -frequency horn cutoff of about Klipsch patents. The Electro -Voice New standards of excellence 40 cps! How can this be reconciled Patrician (Fig. 8) and the James B. in kit cabinetry with the claims of the little cigar boxes Courtesy Audio Research Lab. which purportedly allow you to "hear NO RISK HOME TRIAL all those bass tones to 16 cps?" This It's true-a speaker enclosure you may test contradiction can, I think, be explained in your own home with your own equipment -and in money saving KIT form! by three facts: 1) The cigar box claims are exag- SUPERIOR PERFORMANCE gerated. There is not a commercial Acousti-Magic incorporates a highly refined, speaker system TUNABLE labyrinth design which allows in- made which will repro- stallation of any speaker with space for duce an audible horn -loaded 16 -cps future expansion to a multiple system. Using tone. only an average $50. speaker, Acousti-Magic 2) The Klipschorn will produce 50 will faithfully reproduce the tremendous pedal tones of the mighty organ. Correct acoustical cps at good volume and negligible ( less loading . enables you to FEEL fundamental than 5% ) distortion. You would have bass to 30 cycles and below. to search the entire frequency range of most cigar -box units to find any fre- SUPERIOR KIT DESIGN quencies Acousti-Magic is prefabricated entirely of approaching this distortion 3/4" plywood. Professional lock -mitre pints figure. There are some quite small join the furniture plywood exterior panels- units for which this isn't true, but they but you use NO CLAMPS or NAILS in the as- aren't horn -loaded. sembly. EXCLUSIVE Acousti-Magic construction with MACHINE SCREWS allows effortless The Klipschorn uses a 3) special assembly with only a screwdriver in 2-4 hours. Courtesy Electro-Voice, Inc. Over one hundred pounds of the very finest materials. Fig. 12. Ceramex horn out of cabinet. SUPERIOR STYLING Lansing Hartsfield (Fig. 9) are both Aousti-Magic gives you styling and quality examples of deluxe Klipsch-inspired de- to complement the finest home. The EX- signs. Klipsch has also experimented CLUSIVE CONVERTI -BASE gives you highboy with the idea of using a back-loaded or lowboy styling in an instant-and either horn to boost the bass response of an way you will see nothing but furniture. There are no gimmicks-you don't paint it, you ordinary cone speaker. Fig. 10 diagrams don't cover it-it's all genuine furniture ply- the system - it looks very much like wood-more of it than any other kit speaker a bass -reflex cabinet with a horn at- enclosure. tached to the port, and that is precisely ACT NOW-MAIL THIS COUPON! what it is. Order Acousti-Magic in either hardwood The loading effect of the horn makes Mahogany or Oak. When you receive your the cabinet act as an infinite baffle over kit, assemble it without glue and test it for most of its frequency range. At progres- two weeks. It must give complete satisfaction -sound If sively frequencies mass effect and sight! not, disassemble it and lower the return it for a full refund. short horn, with the of the acting For 12" or 15" Speakers & Multiple Systems acoustic capacity of the rear chamber, introduces increasing phase shift. The Fig. rr. The Baronet rear -loading horn. Acoustical Development Corporation small amount of radiation above reso- Box 572, Hempstead, N. Y. nance in this enclosure is more effi- trick to reproduce frequencies below the I Prefer Acousti-Magic ciently put to use than in a reflex cutoff of the horn. in OAK $64.75 in MAHOGANY D $59.75 We have already said that below cabinet, since the horn increases port efficiency somewhat. My speaker Speaker cutoff, a horn acts as though an addi- system is Size tional mass had been added to the At resonance, the system behaves ex- Send Illustrated Brochure actly as a bass -reflex cabinet with the speaker cone. In the Klipschorn this Name total reactance is designed to resonate port and the speaker operating out of with the acoustic capacitance of the phase with each other to increase the Address enclosed back chamber at about 40 cps. Continued on next page City

DECEMBER 1956 39 I ,: ..JENSEN K-210

SPEAKER WITH NO BAFFLE SPEAKER WITH NO RAFFLE -- - SPEAKER IN CERAMEX. HORN - -SPEAKER IN CERAHEX HORN

o IK K 10 20 30 50 70 100 200 300 500 700 IK 2K 0 50 70 100 200 300 500 700 FREQUENCY IN CPS FREQUENCY IN CPS Fig. 13. Impedance curves of two typical loudspeakers, when unmounted and when mounted in the author's horn enclosure.

LOUDSPEAKERS horn length, and rate of flare are in the impedance curve below 500 cps. juggled around to achieve best results is Since the speaker is loaded acoustically Continued from preceding page far better left to Mr. Klipsch than to we would expect impedance variations you or me, and the fact is he has done due to cone resonances to be evened out. effective radiating area. But above the it quite effectively with at least three So long as the horn operates as a horn, resonant frequency of the system, the speaker enclosures smaller than the full- this is just what happens. In most com- similarity to a bass -reflex cabinet ends. sized Klipschorn. Fig. 11 shows the mercial systems, however, some sort of Whereas the mass of air in the port of Electro -Voice Baronet which utilizes acoustic resonance is employed to re- a Helmholtz resonator remains constant á back -load design in an extremely vive the drooping bass notes and this regardless of frequency, a horn has a compact unit. introduces new peaks in the impedance mass characteristic only below cutoff. In the September issue of AUDIO - characteristics. These are not necessarily Above its cutoff frequency, the short CRAFT we discussed the relationship of related to the acoustic output of the horn acts as a resistive load on the port; cone motion to speaker impedance at system, although they do indicate that by thus utilizing this peculiar property low frequencies, and found that the damping is practically nonexistent at of horns, very smooth bass response can two were directly related. If a horn certain points. be achieved. actually offers a resistive load to its A system which illustrates the Exactly how the enclosure volume, driver, this should therefore be reflected smoothing effect of horn loading without any additional acoustic dodges is shown (without the exterior cabinet) in Fig. 12. The unit is my own Cera- for the first time! mex speaker system - simply a vertical horn having a radial mouth at floor level. A 12 -inch speaker is unity - coupled to the throat of the horn, and the whole affair is made of vermiculite - impregnated concrete to eliminate spuri- ous panel resonances. A full description and construction details of the system have already been given elsewhere.* The reason I bring it up in this connection is that it is about DO-IT-YOURSELF as simple a horn - type enclosure as is possible to design, and its impedance curves consequently TEST RECORDS reflect the effects of horn loading and Fix and Test Your Hi-Fi System little else. The curves in Fig. 13 in- So easy, so simple to fix your Hi-Fi system dicate that the horn does provide re- with any one of these records. Instructions sistive loading to the speaker diaphragm and tests are in plain layman's language. No and smooths out technical knowledge required. impedance variations 8N'' to a surprising degree. QUIET, PLEASE! Checks rumble. One of the interesting WHAT! NO. HUM! Measures hum. things about such a resistive -loaded speaker HOW'S YOUR STYLUS? Stylus wear test. system is the lack of bass distortion TRACKING SPECIAL! Measures funda- and dou- mental arm resonance, analyzes damp- bling. Below the cutoff of the horn ing problems. (60 cps) the response simply disap- VERTICAL/LATERAL RESPONSE! Measures pears, with no usable reproduction be- ratio of vertical to lateral response. low 50 cps. But have you ever heard PERFECT CHRISTMAS GIFT - for WOW! & FLUTTER, TOO! Checks wow 50 cps uncluttered with the hoots and and Christmas, give your Hi-Fi friends flutter. rattles of panel resonances, hang -over one or all six of these records. AVAILABLE AT YOUR HIGH FIDELITY DEALER effects, and frequency doubling? The bass response of such a speaker sounds Corporation more impressive than many other en- Components *Augspurger, George. "A Horn -Type Speaker for DENVILLE, NEW JERSEY Golden Ears." Radio -Electronics, XXVII (Apr, 1956), 34-35.

40 AUDIOCRAFT MAGAZINE closures which measure up far better drawback to these discs ( and that only on a frequency graph. for the special purposes of this depart- The more expensive horn -type sys- ment) is that the immaculate recording tems, such as the Klipschorn, Patrician, tends to be entirely overlooked as one and Hartsfield, have special bass drivers succumbs to the sheer magic of expres- designed specifically for use in their sive organ tone and Bach's incomparably particular enclosures. The mere addi- zestful contrapuntal textures. tion of a jerry-rigged horn to an or- I have never been able to understand dinary speaker is not the same as an why these particular works aren't heard integrated system, and some designers more often and are not far more en- have been unjustly skeptical of horn thusiastically acclaimed; teaching pieces design for quality reproduction. In though they may be by intent, they answer to such views, we can do no seem to me to distill much of the better than heed one last warning from quintessence of Bach's most distinctive Voigt: "The experimenter should bear art. Listen to the now -jubilant, now - in mind that speakers developed for use eloquent Fifth Sonata for a starter, and with normal baffles or enclosures are not I can't imagine your ever again passing necessarily suitable for use with horns. over or belittling the Bachian trio - In an ideal arrangement, the drive unit sonatas. and the horn are designed as a matching pair, and if this is done properly, Bowed Strings and Twanged results can be breathtakingly lifelike." Continuo In attempting to turn some hi-fi SOUND FANCIER aficionados at least temporarily from big Continued from page 28 display orchestrations to the very different yet no less kaleidoscopic tone painting of familiar. These three canzonettas and the baroque organ literature, I feel I have a fair chance of success. six canzonas reveal that the great pre - In But I'm doubtful about the stringed your audio dealer's demonstration room where Bach virtuoso had a gift for melodic loudspeakers are lined up all in a military row music of the same era. For here charm and pungent humor that is no the ...look for the speaker with the large, silvery sonic colors are durai dome in the center. Ear -test it with special less distinctive than the intricate archi- less immediately novel and even more subtle, and - care. This is the Jim Lansing Signature 0130- tecture in tone for which he is most to the un alerted or unsympathetic ear many of the 15" Extended Range Speaker with 4" voice famous. They happen to be historically coil of edge -wound aluminum ribbon. The coil is these works sound much important little pieces for the light they alike. It takes attached directly to the 4" durst dome. Together close familiarity with they give the piston assembly rigid- throw on the development of this fugue, the characteristic exceptional idioms and sonorities to recognize the ity. This is one reason why bass tones sound so but luckily you don't have to be a actually highly differentiated individ- crisp and clean ... why the highs so smooth ... musicologist to relish immediately such the mid -range so well-defined. You will find the ualities of style. That comes delights as the cool loveliness of the ele- easily D130 to be as distinguished to your ear as it is enough if you're willing to make the to your eye. giac E minor Canzonetta (to cite a effort, but meanwhile perhaps the best single example only) or the enchanting THE SIGNATURE D130 (shown above) first approach is merely to develop coloring of Linder's poetically devised an IS YOUR BASIC SPEAKER appreciation of the distinctive registrations, caught to perfection in combina- Use it alone when you first begin your high tion of smooth spaciously open acoustics and recording. string and twangy harp- fidelity system. Perfectly balanced with other sichord (continuo) tones. Signature units, it later serves as a low fre- Talking with a number of organ con- One way is quency unit in your divided network system. noisseurs about the works reviewed here to study performances which compromise to with Transducers earlier (the serious ones, that is; I'm some extent Additional Signature Precision baroque ideals by blending with large domes and voice coils: trying to forget the sore subject of timbres more suavely and phrasing more ex- theater organs at least for a while!), SIGNATURE 0131... pressively, thus making them resemble the finest 12" speaker made every one of them ended up by demand- 0.D: 127/8" more ing, "But have you heard the magnifi- closely the later strings-only en- 4" voice coil of edge -wound semble playing with which we are most aluminum ribbon cent Walcha Archive series?" I hadn't Depth -5" familiar. A good example is the ex- Power input -20 watts then, and knew the blind German Impedance -16 ohms tremely skillful I Musici group's player only by some of his Decca re- playing of five concerti grossi, including, appro- SIGNATURE 0123... leases of several years ago, which were an innovation in speaker design priately De.0pt.h-127o/e"nly 3%" pleasant enough, but hardly especially enough for this month, the so- called Christmas 0 impressive. But when specialists who Concerto, No. 6 in G 3" voice coil of edge -wound minor (Epic LC 3217). Yet although aluminum ribbon seldom if ever rave ecstatically about Power input -20 watts the music is ingratiating Impedance -16 ohms any record seemed so excited, I felt and the recording admirably that something new must have been clean, Ì never get SIGNATURE D208... what seem to me the essential baroque an 8" precision transducer added to Walcha's work - and my first O.D.- 87/4" characteristics, especially the 2" voice coil of edge -wound encounter with the new series is more bite and ring of the harpsicord's aluminum ribbon than enough to confirm that feeling. supporting role Power input -12 watts here far too Impedance -D208-8 ohms For Walcha now is surely - discreetly integrated into one of the 0216-16 ohms the tonal fabric. warmest and most endearing of all for chtalog Going directly to stylistically See your audio dealer complete Bach interpreters and, as heard here on more authentic, even less the 1695 Schnitger organ at Cappel if polished, performances is by far the better way and the even more ancient small organ - every note a perfect quote provided of St. Jacobi's at Lübeck, he provides only that you refuse to be discouraged or te perhaps the most ingratiating and per- repelled by what may suasive seem like thinness and brittleness at of all possible introductions to "JBL" means JAMES B. LANSING SOUND, INC. the sonic spells of the baroque. The only Continued on next page 2439 Fletcher Drive, Los Angeles 39, Calif.

DECEMBER 1956 41 AUDIOCRAFT SOUND FANCIER Continued from preceding page

Sound Sales Directory first acquaintance. I experienced this Following is a list of dealers who state that they carry the products specified. feeling, too, when I first started to play the Cambridge Society for Early Music MASSACHUSETTS disc (Unicorn 1030) starring violinists KEY TO PRODUCTS HANDLED r Audio system components Boston Ruth Posselt and Richard Burgin in 2 Speakers and enclosures The Listening Post, Inc. concertos by Vivaldi and Torelli (one 3 Records and record accessories 161 Newbury St. not included in the Epic record above) 4 Tape recorders COpley 7-7530 1, 2, 4, 5, 8-10 and sonatas by Dall' Abaco, Veracini, 5 Pre-recorded tape 6 Radio hardware and Albinoni. For this is the first re- 7 Tools, wood MISSOURI cording I know to have been made in 8 Audio parts St. Louis my favorite auditorium for concert lis- 9 Microphones tening, Sanders Theater in Memorial ro Books The High Fidelity Showroom z t Test equipment 6383 Clayton Rd. Hall at Cambridge, Massachusetts, A series of items numbered consecutively is Parkview 1-6500 1-5, 9 which I remember best for its incompar- identified by a hyphen between the first and last numbers. Thus, 1-6 indicates 1 through ably live acoustics as excited by the 6; 8-11 indicates 8, 9, 10, and 11. Boston Symphony in full blast. But the NEW JERSEY New Brunswick initial impression of thinness quickly disappeared as my ears became ac- CALIFORNIA Monmouth Music House customed to the very different demands Beverly Hills 215 Bevier Road CHarter 9-5130 1, 2, 4, 5, 9 of this music. And long before it was Minthorne Music of Beverly Hills 230 N. Beverly Dr. finished I had been persuaded that I'd BR. 2-7676; CR. 6-4793 1-5, 9 never heard the combination of a few NEW YORK strings and harpsichord (here played Hollywood Albany as boldly as it should be, in freely ex- Hollywood Electronics Audio -Video Corporation fashion, by Erwin Bodky ) 7460 Melrose Ave. 324 Central Ave. temporaneous Webster 3-8208 1, 2, 4, 5 3-1167 1-5, 8-10 captured more authentically. Peter Amsterdam Bartók has made many more sensational and obviously brilliant recordings CONNECTICUT Adirondack Radio Supply 185-191 West Main St. than this, but I doubt whether even he West Hartford VI. 2-8350 1, 2, 4, 8 has ever achieved a more candidly Audio Workshop, Inc. Buffalo honest one. And at least one of the 1 South Main St. Frontier Electronics, Inc. Adams 3-5041 1-5, 9, 10 works included here ranks among those 1507 Main St. no one, whatever his tastes, should miss; GA. 5727 1-5, 8-10 if has been only a to New York City Albinoni name DELAWARE you before, once you hear his Trio - Newark Arrow Audio Center 65 Cortlandt St. Sonata in A major, Op. 1, No. 3, you'll Delaware Music House Dlgby 9-4730 1, 2, 4-6, 8-11 esteem him forevermore among the 20 Academy St. most captivating of musical personali- Endicott 8-3258 1-5, 8, 9 ties! PENNSYLVANIA GEORGIA Philadelphia Plucked Strings Solo Atlanta Danby Radio Corp. If you've been exposed to so much hi-fi 19 South 21st St. Baker Fidelity Corp. Rittenhouse 6-5686 1-5, 8-10 percussion indoctrination that the ictus 1140 Peachtree St., N. E. of harpsichord tone attack and the gut Radio Electric Ser. Co. of Pa., Inc. TRinity 5-2156 1-6, 8, 9 7th & Arch Sts. bite of a rosined bow don't pack enough LO. 3-5840 kick for your overstimulated aural ap- I have the ) ILLINOIS Ten Cate Associates petites, still means (I hope! Chicago 6128 Morton St. to win you over to baroque strings. Germantown 8-5448 1-5, 8-10 Just give me or rather, Michel Podol- Allied Radio Corp. - 100 N. Western Ave. ski's Bach Works for the Lute (Period HAymarket 1.6800 1.11 SPL 724) -a fair chance! But first WASHINGTON relax, turn the volume control down Evergreen Allied High Fidelity, Inc. Seattle 2025 W. 95th (for the tiny-voiced Lute is consider- St. High Fidelity Headquarters BEverly 8-1067 ably enlarged here, if miraculously quite 603 Broadway North Evanston CApitol 2266 1-4, 8, 10 without distortion) , and prepare to a strange, but wholly bewitching, Allied High Fidelity Stores, Inc. enter 602 Davis St. new world of sound. In their own ways, DAvis 8-8822 WEST VIRGINIA these two suites (one usually heard in Oak Park Charleston an unaccompanied cello version) and West Suburban Allied High Fidelity, Inc. Electronic Specialty Co. a Prelude and Fugue in E Flat offer 7055 W. North Ave. Virginia Street W., At Park Avenue sonic enticements, and even excitements, EStebrook 9-4281 1-11 3-5656 1-11 which are in microcosm quite comparable to those commanded, on an infinitely larger scale, by, say, Ravel's LOUISIANA CANADA Daphnis et Chloé. New Orleans. Montreal (Well, maybe I'm exaggerating just The Music Shop, Inc. Payette Radio Limited 4215 South Claiborne Ave. 730 St. James West a bit, but [boy scout's oath!) that's TW. 1-5871 1-5 UNiversity 6-6681 the way I feel while I'm hypnotized by

42 AUDIOCRAFT MAGAZINE some of the most novel, refreshing, and the grinder by a belt. With the latter, expressive timbres I've ever encountered the side of the motor shaft which is not on records or off.) turning the belt can be fitted to take However, if you're a bit timid about the accessory wheels thereby making it jumping cold, at it were, from more unnecessary to remove the abrasive romantic music and instruments directly into what you may fear are the too remote baroque lutenist domains, there i are convenient stepping stones in the form of solo Spanish guitar recordings, whose brighter, bolder, more incisive PRECISION tonal qualities well may be more ex- \ citing at first hearing, if scarcely as that speaks i f or itself ! deeply satisfying in the long run. Two particularly good ones I've heard recently are Laurindo Almeida's Guitar Music of Spain (transcriptions of Precision construction throughout! This is the reason Albéniz and Falla, plus originals by why Jim Lansing Signature High Frequency Units are Sor, Segovia, Tárrega, and Tórroba; "speak" with unequaled fidelity. Diaphragms made of aluminum, hydraulically-formed for complete Capitol P 8295 ), and Mario Escudero's uniformity and homogeneity of grain structure. Phas- Flamenco (Phototapes -Sonore PM 5008, ing plugs are machined to micrometric dimensions from solid billets of absolutely pure iron. Exponential or Folkways LP 920) . The former horns are machined from aluminum castings. Kous- is perhaps the more immediately ap- tical Lenses are cut, formed and assembled to optical tolerances. The greatly superior reproduction ...the pealing for its warmly expressive ease with which transients are handled ...which re- playing of highly atmospheric Iberian sult from this detailed precision are immediately mood music, but the latter, with its apparent to your ear. You hear a complete, flat, smooth high end free from disturbing dips and star- more scintillating tonal qualities and tling peaks. electrifying Gypsy passion, is likely to Fig. 7. Sharpening a mortising chisel. make a more dramatic impact on hi-fi SIGNATURE 175DLH TRANSDUCER ears, as well as provide an even sterner wheel in order to polish or buff or PRECISION HIGH FREQUENCY test of hi-fi systems' transient responses. brush. Pictured above, the 175DLH is the first assembly ever placed on the high fidelity market to incorporate a Though most grinders come equipped true acoustic lens. With 14 separate elements, thé with wheel guards or special shields to lens distributes sound smoothly over a 90° solid WOODCRAFTER protect the operator from flying sparks angle. Index of refraction 1.3. Designed for 1200 cycle crossover. 16 ohms impedance. 25 watts power Continued from page .2- and particles, the wise craftsman will Input above 1200 c.p.s. always wear approved safety goggles use is the combination stone, coarse on when using the machine. one side and fine on the other. Before SIGNATURE 375 using it for the first time, soak the stone PRECISION HIGH FREQUENCY TRANSDUCER This driver, alone, weighs 31 overnight in a mixture of equal parts AM CRYSTAL TUNER pounds! With a 4" voice coil and of machine oil and kerosene. There- diaphragm it is unquestionably the after, lubricate the surface with the same Continued from page 18 largest and most capable high frequency unit manufactured. De- mixture each time the stone is used, identical to that for the previous tuner. signed for theater systems; used and make certain that it is free of dust in The Hartsfield. Low crossover - Circuit values differ slightly in some 500 is the secret of the and grime. Before putting the stone c.p.s-- respects, and a volume control has been impressive illusion of presence it away, wipe it clean with a cloth and creates. Power input -60 watts added. The physical arrangement of store it in a dust -free container. If the above 300 c.p.s. Impedance -16 parts is, however, quite different; for ohms. Flux density-over 20,000 surface becomes gummy, warm the stone example, components grouped together gauss. in an oven and it will wipe clean easily. When honing, utilize the entire face SIGNATURE 537-500 HORN-LENS ASSEMBLY wearing it of the stone to avoid un- This is a round exponential horn evenly and forming hollows. Should the and lens for use with the 375 Sig- stone become hollowed, it can be made nature Driver. Lens composed of 19 separate elements for smooth dis- level again by several methods: rub it tribution of highs. Diameter, 131/2". flat on a smooth iron surface using kerosene and emery powder as an abrasive; rub it on a piece of glass using 80 -grit SIGNATURE 537-509 HORN -LENS ASSEMBLY silicon -carbide powder and water; or Consisting of a rectangular grind it flat on coarse garnet paper. exponential horn and serpentine The Power Grinder: When cutting Koustical Lens (as used in The Hartsfield), this assembly provides edges of tools are damaged, or worn Wiring board in place inside cabinet. wide horizontal and narrow vertical beyond restoration by an oilstone, a coverage in order to minimize ceil- in the coil cans of Dr. Stern's tuner ing and floor reflections. Use with power grinder can often come to the are separated in the 565 kit. the 375 Driver. Lens is 20" wide. rescue. In a workshop equipped with All electrical parts are mounted on a hand tools or power tools, the grinder wiring board that is inscribed on both serves a variety of purposes: sharpening, with picture outlines of each part buffing, polishing, wire brushing, and sides every note a perfect quote where it is to be placed, and with lines other tasks, all performed by various showing where interconnecting wires are JTG/i'GGf.I accessories. In some machines the motor to go. The board is punched at appro- is part of the main assembly, while in "iBL" means JAMES B. LANSING SOUND, INC. 2439 Fletcher Drive. Los Angeles 39, Calif. others the motor is separate, driving Continued on next page

DECEMBER 1956 43 AM CRYSTAL TUNER PROFESSIONAL Continued from preceding page DIRECTORY the ultimate goal priate places and metal eyelets are al- TRIAL OFFER of the ready inserted in the holes; these eyelets serve as easily soldered connecting ter- 12 for $1.00 listener minals, as can be seen in the photo- Twelve -Inch Record graphs. When the wiring is completed COVERS according to the step-by-step instruc- shipped prepaid tions furnished, the board is attached Money Back GUARANTEE inside the front panel of the 31/2 by Made of Polyethylene Plastic. 4 by 7 -inch cabinet with the tuning - Slips Inside Original Jacket Keep your valuable records free from dust. capacitor and volume -control shafts pro- scratches, finger marks, spilled liquids, etc. jecting through. The brass escutcheon Introductory SAMPLER DOZEN and j, SURPRISE BONUS $1.00 Prepaid Dealer Inquiries Invited preamplifier,' complete '$168` BRADLEY MfC. INC. 11 W. Magnolia Blvd. Burbank, Calif.

. $198* Artisan "slightly higher west of Front side of the wiring board assembly. Dead /t- Yourself the Mississippi is attached at the same time. Then the ELECTRONIC ORGANS knobs and dial indicator are control Send $1.00 for "Organ Builders Manual" write for literature slipped on the shafts; the job is finished. It took us 21/4 hours for everything. ELECTRONIC ORGAN ARTS found that the had slightly 4878 Eagle Rock Blvd. maranlz company; We 565 Los Angeles 41, Calif. greater sensitivity and selectivity than 44-15 Vernòn Blvd., tang Island City 1, N. `Y. the other tuner. Sound quality was identical, as nearly as we could judge. Other advantages: it isn't necessary to Rife order the parts individually, then scribe systems and cut the chassis; the 565 is more antenna compact and better looking; it is almost High gain broadband FM Antennae for max. impossible to make a mistake in its tuner sensitivity to 72 or 300 ohm inputs. Pro- vides optimum signal level for best recording for everything in assembly; an audio -output cable is sup- of high fidelity broadcasts. hi-fi plied; the tuning dial is vernier -driven, APPARATUS DEVELOPMENT CO. GET THE MONEY -SAVING 1957 so that it is smoother and more precise in operation. The volume control may FM/Q Dept. Wethersfield 9, Conn. ALLIED CATALOG not be so advantageous because, over much of its operating range, it can produce a sloping high -frequency response featuring the TRADERS' MARKETPLACE it is safer to leave it turned all the world's largest - Here's the place to buy, swap, or sell way on. stocks of systems audio equipment. Rates are only zoe a The 565, although a little more ex- & components word (including address) and your ad- pensive than the other tuner, is still vertisement will reach zo,000 to 35,000 readers. Remittance must accompany free! copy and insertion instructions. SEND FOR IT COMPLETE, RELIABLE MAIL ORDER record service. Catalogs free. Helmer, Box 193, Oneida, N. Y. Here's your complete money -saving guide to Hi-Fi. Shows you how to select a cus- TAPE RECORDERS, tape. Unusual values. Free tom Hi-Fi music system for your home at catalog. Dressner, 69-02D, 174 St., Flushing 65, no more than the cost of an ordinary N. Y. phonograph. Tells you what to look fur and how to save money. Offers the world's largest selection of complete Hi-Fi systems as well as individual amplifiers, READERS' FORUM tuners, changers, speakers, enclosures and accessories. Want to build-your-own?- see the famous Hi-Fi KNIGHT -KITS. For Continued from page 15 everything in Hi-Fi-for everything in Elec- Appearance of the finished 565 tuner. tronics, get the FREE 1957 ALLIED Catalog. trouble, particularly if the music were an excellent buy because of its far copyrighted. The only possible excep- ALLIED RADIO HI-ERICA'S FI CENTER better appearance, additional conven- tion would be the use of such a re- ALLIED RADIO CORP. Dept. MM -126 ience features, and ease of assembly. If cording to demonstrate the capabilities 100 N. Western Ave., Chicago 80, III. you delight in doing all your own work of receiving or recording gear, and even D Send FREE 1957 ALLIED Catalog fi (even to chassis -cutting) , or if the in such instances the recordist would Name lower cost appeals to you, then Dr. do well to avoid making or using tapes u Address Stern's tuner offers virtually as good of complete musical selections. y performance at an even smaller invest- There remains the question of tape is Zone State City ment. recordings from broadcasts which are

44 AUDIOCRAFT MAGAZINE used by the home recordist for the ADVERTISING public or private entertainment of groups of people, where there is no .. INDEX commercial intention on the part of =c°...,- the recordist. If the home tape is a copy of the music only from a com- Acoustic Research, Inc..... 32-33 mercial recording and contains complete musical selections and the recordist's Acoustical Development tape were made with the intention of avoiding the use or purchase of the Corp. 39 = --14_ ,1. commercial recording, I should think he f -_. Allied Radio Corp. 44 could get into serious trouble. If the recording is of special material broad- Amperex Electronic Corp. 37 cast by the station, not ordinarily available on commercial recording, my sug- Apparatus Development Co 44 gestion to the recordist would be to get in touch with the responsible executive Audio Fidelity Records (usually the Program Director) of the Inside Front Cover station recorded to see whether permission to use the tape can be obtained. Audio League 34 This can take quite a bit of doing, for chances are that the station cannot give Audiophile's Bookshelf 1 the permission itself, but can only tell one whom to ask. And, of course, this Berlant Co. 12-13 implies that the recordist is telling the station and others that he has made the Bradley Mfg. Co. 44 recording, which could be enough to "Pleasant to look at"-they say about Jim Lansing Signature speaker enclosures. Certainly, their lines are get him into trouble by itself. The best clean, well-proportioned.... "Chaste,' one writer said. Components Corp. 40 policy, though, is openly and clearly And the way they look does have something to do with Their appearance has developed to obtain permission before playing a the way they sound. Cook Laboratories 31 from the function they perform. Further, you can see tape obtained from a broadcast before and feel their solid construction. any group of people (and, I suppose, To bring out the best sound available from your Sig- Dauntless International nature precision transducers, Signature enclosures are particularly before any group of people carefully engineered. It is necessary to match the Inside Front Cover not likely to have heard the original acoustical impedance of the cabinet with the impedance of the speaker or network (and speakers) for optimum broadcast). performance. Highly skilled craftsmen, working to the Eico 46 All this may sound very strict and closest tolerances, use the most advanced methods of unencouraging, especially when one con- cabinet fabrication in constructing Signature enclosures. Electro -Voice, Durable, hand -rubbed finishes to match your home dec- Inc. 36 siders the amount of such taping going oration are available. To hear everything your Jim on. The situation is somewhat analo- Lansing Signature precision transducers can offer, in- Electronic Organ Arts 44 gous to speeding on the highway: it's stall them in a Signature precision enclosure. Heath Co. SIGNATURE C37 (shown above) 8-9 LOWBOY REFLEX ENCLOSURE A new "basis for comparison" is established with the Jensen Mfg. Co. 2 introduction of the new Signature C37 low-boy reflex enclosure. This model is similar in dimensions and performance, to the Signature C35, still the standard of Klipsch and Associates 46 the industry. Use with any Signature Extended Range Speaker, or with a Signature two-way divided network Lansing, James B., Sound, system. against the law; nobody seriously recom- Inc. 41, 43, 45 SIGNATURE C34 mends the infraction; violators are often BACK -LOADED CORNER severely punished, although just as often HORN Marantz Co. 44 CONSOLE they get off quite lightly; and the bulk The most popular enclosure Miller, J. Co. of the infractions remain undetected in the Signature line, the C34 W., 35 may be used either in a cor- and unpunished. ner or against a flat wall. MusiCraft 1 i Speaking officially for WCRB, I Use with either a D130 Ex- should like it to be clearly known that tended Range Speaker or a 001 two-way system. Six foot North American Phillips we take a dim view of most of such exponential horn, driven by recording. We shall co-operate with back of speaker adds an extra Co. Inside Back Cover octave of clean bass. Above any recording company which may wish 150 c.o.s. front of speaker Professional Directory 44 to take action against any of our lis- acts as direct radiator. teners who copy commercial recorded Regency Division, I.D.E.A., material broadcast by the station, and we shall take prompt action against Your audio dealer can supply you with Inc. 38 plans for constructing these and other Signature those who record our own material and enclosures. Sound Sales Directory attempt to use it in any way without 42 our prior permission. Stephens Tm -Sonic, Broadcast musical programs are in- Inc. Back Cover tended for one time enjoyment in lis- every note a perfect quote teners' homes; commercial recordings are Traders' Marketplace made and sold to provide repeated hear- 44 ings in the listeners' homes. We work "JBL" means JAMES B. LANSING SOUND, INC. University Loudspeakers, Inc... 5 Continued on next page 2439 Fletcher Drive, Los Angeles 39, Calif.

DECEMBER 1956 45 READERS' FORUM some degradation in quality from the gfigi'i J;cl

AUDIOCRAFT MAGAZINE 46 Electro -Voice Centurion Kit: an AUDIOCRAFT Frequency Response of Inner Loop, p. 30; Record Changers; Dec. 55, p. 10. External Kit Report; Jul. 56, pp. 16-18, 31, 33. Low -Frequency Response, Outer Loop, p. 30; Noises; Dec. 55, pp. 10, 4647. How Much Construction Notes, pp. 17-18, 31; AUDIO - High -Frequency Response, Outer Loop, pp. Hum?; Jan. 56, p. 10. Hiss and Sizzle; Jan. CRAFT Test Results, pp. 31, 33. 30, 45; Power Supply Components, p. 45. 56, p. 10. Amplifier Bass Stability; Feb. Building the Jensen Imperial: Karl Kramer; FM Antenna Systems: L. F. B. Carini; Jul. 56, 56, pp. 10, 42. Treble Amplifier Stability; Nov. 55, pp. 18-20, 3840. KT -31 Kit Parts pp. 20-21, 35; Balanced or Unbalanced, p. Mar. 56, p. 8. Checking Out Your Ampli- List, p. 18; Building the Cabinet, pp. 18-20; 20; Impedance Matching, p. 20; Use of the fier; Apr. 56, p. 10. Down With Distortion; Cabinet Materials List, p. 20; Installing the Bailin, pp. 20-21; FM Sensitivity Ratings, p. May 56, pp. 10-11. Loudspeakers: Part I; Speaker Units, pp. 20, 38-39. 21; 72 vs. 300 Ohms, p. 21; Other Imped- June 56, pp. 10-11, 36; Part II; Jul. 56, pp. A Home -Built Pickup Arm: J. E. Richardson; ances, p. 21; Comparative Tests, pp. 21, 9-10; Part III; Aug. 56, pp. 10-11; Part IV; May 56, pp. 26-27, 40. List of Materials, pp. 35; Summary, p. 35. Sept. 56, pp. 12-13. What Not to Service; 26-27; Construction, pp. 27, 40; Final As- The Grounded Ear: Joseph Marshall. Mallard Oct. 56, pp. 12; 55-56. sembly, p. 40. Circuit; Nov. 55, p. 10. New Audio Tubes; Tape News and Views: J. Gordon Holt. Pre- Hi Fi Pure and Simple: Lee Beeder; Aug. 56, Nov. 55, pp. 10, 40-41. Cascode Preampli- ventive Maintenance; Jul. 56, pp. 12-13, pp. 22-23, 35. Crossover Network, pp. 23, fiers; Dec. 55, p. 4. Corner Coupler; Dec. 3940. Microphone Maintenance; Nov. 56, 35. 55, pp. 4-5. Moving -Needle Pickup; Dec. pp. 14, 4142. How They Did It: 55, pp. 5, 43. Stereo High Fidelity; Jan. 56, Tips for the Woodcrafter: George Bowe. Main- Binding A Tape Library; John Hoke; Dec. pp. 4, 32. Here We Go Again?; Feb. 56, tenance of Hand Tools; Nov. 56, pp. 10-11, 55, pp. 36-37. p. 4. The 1/2 -Mil Microgroove Stylus; Feb. 13, 42. Sharpening Power Tools; Dec. 56, Carnegie Hall on Wheels; Brooking Tatum; 56, pp. 4-5. Radioactive Pickups; Feb. 56. pp. 10-11, 43. Jan. 56, pp. 24-25, 36. pp. 5, 41. Modern Design; Mar. 56, pp. 4-5. Tape Recording and Playback Installation; Some New Products; Mar. 56, p. 5. Goodbye, MISCELLANEOUS Richard H. Cobb, Jr.; Nov. 55; pp. 34-35. Hi-Fi Records; Apr. 56, p. 4. How Much The Grounded Ear: Joseph Marshall. Better Lebensraum for the Craftsman: R. D. Darrell; Power?; Apr. 56, pp, 4-5, 40. How Much pp. 4-5. Destati- Nov. It Easy Hi Fi Promotion; Aug. 56, 55, pp. 33, 38. Make for Your- Feedback?; May 56, pp. 4-5. How Big a cized Records; Nov. 56, p. 5. self!, pp. 33, 38; Safety Precautions, p. 38. Speaker Cone?; May 56, pp. 5, 4445. Fair- May pp. 24-25, 41. Load It B. A Hi-Fi Milestone: 56, With Sand: Ernest Schoedsack; Dec. child Elliptical Stylus; May 56, p. 45. What Recording at MIT: Dec. 56, pp. 22-23, 34. 55, pp. 32, 4143. Makes a Pickup?; May 56, p. 45. Mira - Making the University Classic: Abraham B. Cohen; Feb. 56, pp. 17-18, 37. RECORDING More Multi Than Most: Ronald Lowdermilk; The Grounded Ear: Joseph Marshall. Those Apr. 56, pp. 22-24, 43. Overcut Records; Aug. 56, p. 5. Tape Qual- Optical Tape Timer: John J. Stern, M.D.; May ity; Dec. 56, p. 4. Disc Recordings; Dec. 56, p. 35. 56, pp. 4-5, 37. The Sherwood Forester: an AUDIOCRAFT Kit Microphone Roundup: J. Gordon Holt; Nov. Report; Sept. 56, pp. 18-20, 34-35. Cabinet 55, pp. 28-30. Assembly, pp. 18-20; Final Assembly, p. 20; Stereo Recording with a Pentron: Glen South - Finishing the Enclosure, pp. 20, 34-35; twin Cartridge; June 56, pp. 5, 36. The Slot worth; Jan. 56, pp. 19, 37-38. AUDIOCRAFT Test Results, p. 35. Radiator; Jul. 56, p. 4. Marantz Amplifier; Tape News and Views: J. Gordon Holt. Com- Speaker Enclosures: Types and Designs: Edgar Sept. 56, pp. 4-5. New Screen -Feedback Idea; patibility . . A Sour Note; .Nov. 55, pp. M. Villchur; Dec. 55, pp. 18-20, 40-41. Sept. 56, pp. 5, 42. Electrostatic Loud- 12, 40. More on Incompatibility; Dec. 55, Wall Mounting, pp. 18-19; Total -Enclosure speakers; Oct. 56, pp. 4-5. Acoustic Resistance pp. 12-14. Head Alignment; Dec. 55, pp. Cabinets, pp. 19-20; Resonant Enclosure, p. Unit; Nov. 56, pp. 4-5. New Cartridge; Nov. 14, 48. Well-Integrated Recorder; Jan. 56, 20; Tuning a Bass-Reflex, pp. 20, 4041; 56, pp. 5, 44. Screen Feedback; Dec. 56, pp. 12-13, 38, 40. Fen -Tone B&O 50; Jan. Horn, p. 41. P. 37. 56, p. 40. The Prospective Buyer; Feb. 56, A Stereo -Monaural Speaker System: Howard M. Impedances in Multi -Speaker Systems: Paul W. pp. 12-14, 4041. Frequency Response and Van Sickle; Apr. 56, pp. 28-30, 4041. The Klipsch; May 56, pp. 16-17, 4244. Woofer Bias; Mar. 56, pp. 12-13. Tape -Storage Prob- Bass Assembly, pp. 28-30; Cube Enclosures, Impedance, pp. 16-17; Middle -Range Mis- lems; Apr. 56, pp. 12-13, 43-44. Notes on pp. 30, 4041. matches, p. 17; Tweeters, pp. 17, 42; Multi - Control Units; Apr. 56, p. 44. Monitoring That Professional Look: Joseph Marshall; Nov. Speaker Systems, pp. 4243; Pads and At- and Volume Indicators; May 56, pp. 12-13, 55, pp. 21-23. Finishing the Panel, pp. 21. tenuators, p. 43; Conclusion, pp. 4344. 45, 48. Recording from Radio; June 56, pp. 22; Lettering, p. 22; Plexiglas Panels, Es- Minimizing Pickup Tracking Error: Dr. John D. 12-13, 33-35. Hartford Music Festival; Aug. cutcheons, pp. 22-23. Seagrave; Dec. 56, pp. 19-21, 34. Interpret- 56, pp. 12-13, 35, 37. Tapes vs. Discs; Sept. Tips for the Woodcrafter: George Bowe. Basic ing Distortion Index, pp. 20, 34. 56, pp. 14-15, 4243. Hi -Z vs. Lo -Z Micro- Shop Tools; Nov. 55, pp. 16, 44-45. Using Multiple -Speaker Switching Systems: Herman phones; Oct. 56, pp. 14-15. Two More Hand Tools; Dec. 55, pp. 8, 4546. Wood- Burstein; Feb. 56, pp. 22-23, 42. Impedance Microphones; Oct. 56, pp. 15, 51, 53. working Drawings; Jan. 56, pp. 8-9, 35. Matching, pp. 22-23; Individual Volume Con- Testing Recording Tape; Dec. 56, pp. 14, Joinery; Feb. 56, pp. 8-9, 3940. Plywood; trols, p. 23; Switching, pp. 23, 42. 35-37. Mar. 56, pp. 10-11, 4243. Regular Lumber; Music from Electrons: Robert Moog; June 56, Apr. 56, pp. 8-9, 38. List of Types of Wood; pp. 16-19, 33. Pitch Control, pp. 16, 18; RECORD REVIEWS Apr. 56, p. 39. Wood Finishing; May 56, Schematic, p. 17; Harmonic Generation, pp. Sound Fanciers' Guide: R. D. Darrell. Jul. pp. 8-9, 42. Basic Power Tools, Part I; June 18-19; Volume Control, pp. 19, 33. 56, pp. 26-27, 37, 39. Aug. 56, pp. 29-31. 56, pp. 8-9, 35; The Circular Saw, pp. 8-9. Out of the Speaker Into the Room: William C. Sept. 56, pp. 31-34. Oct. 56, pp. 36-39, 44. 35. Basic Power Tools, Part H; Jul. 56, pp. Bohn; Nov. 55, pp. 24-25. Speaker Orienta- Nov. 56, pp. 30-32, 34-35. Dec. 56, pp. 8-9, 35; The Band Saw, pp. 8-9, 35; The Jig tion, pp. 24-25; Room Treatment, p. 25; 28, 4143. Saw, p. 35. Basic Power Tools, Pan III; Aug. Loudspeaker Differences, p. 25. 56, pp. 8-9; The Router, pp. 8-9; The Shaper, Practical Audio Design: Joseph Marshall. Part TEST INSTRUMENTS p. 9. Basic Power Tools, Part IV; Sept. 56, Power Transformers I: and Rectifiers; Jan. AUDIOCRAFT Kit Report; pp. 10-11, 4042; Testing Alignment of The 56, pp. 21-23, 34-36; Choosing a Trans- Eico VTVM Kit: an Table, pp. 10-11, 40; How to Nov. 56, pp. 24-26, 42. Construction Notes, Bore Deep former, pp. 21.23; Making an Old Unit Do, Results, pp. Holes, p. 40; How to Bore Holes in Round p. 23; Modifying Transformers, pp. 23, 34- pp. 25-26; AUDIOCRAFT Test Stock, pp. 4041; How to Make a Mortise, Adjusting Voltage, 26, 42. 35; High p. 35; Trans- -1 Meter: an AUDIOCRAFT pp. 41-42. Basic Power Tools, Part V (the former Ratings, p. 35; AC Load, pp. 35-36. Heath HD Distortion Jointer); Oct. 56, pp. 10-11, 44; Rear Table Part II: Power -Supply Filters; Feb. 56, pp. Kit Report; Aug. 56, pp. 19-21, 34-35. Adjustment, pp. 10-11; Adjusting the Fence, 24-28; Choke-Input Filters, pp. 24-25; Tube Distortion Testing, pp. 19-20; Circuit De- p. 11; Jointing an Edge, pp. 11, 44; Jointing Choice, p. 25; Hum Filtering -General, pp. scription, pp. 20-21; AUDIOCRAFT Test Re- an End, p. 44; Planing a Surface, p. 44; 25-26; Capacitor-Input Design, pp. 26-27; sults, pp. 21, 34-35. Cutting a Rabbet, p. 44; Some Basic Tips on RC Filter Design, pp. 27-28; Choke -Input The Knight Audio Generator: an AUDIOCRAFT Jointer Operation, p. 44. Design, p. 28. Part III: Decoupling Kit Report; May 56, pp. 18-20. Construction Networks AUDIOCRAFT Test Results, Turntable . . with Strings Attached: S. R. and Voltage Regulation; Mar. 56, pp. 35-36, Notes, pp. 18-19; Williams; Dec. 55, pp. 28-31. Noise Reduc- 41.42; Voltage Regulation, pp. 36, 41; Bias pp. 19-20. tion by Inertia, pp. 28-29; Mass Used in Supplies, pp. 41-42. Miniature Signal Injector: Rufus P. Turner; Jul. the Turntable, p. 29; Turntable Design, pp. 56, pp. 22-23, 27, 37. Construction, pp. Speaker System Design Notes: Saul White; Jan. Test 29-30; Construction, p. 31. 56, pp. 20, 34. Test Setup, pp. 20, 34; Test 22-23; Parts List, p. 23; AUDIOCRAFT Yours for the Making Attractive Record - Results, p. 34. Results, pp. 27, 37. Storage Cabinet: S. R. Williams; Feb. 56, Transistors in Audio Circuits: Paul Penfield, Jr. Testing Without Instruments: Glen Southworth; p. 29. II: Miscellaneous Transistor Types, Nov. 56, Mar. 56, pp. 29-31, 40. Localizing the pp. 22-23, Point -Contact Transistors, Trouble, pp. 29-31, 40. DESIGN 36-37; Using Test Instruments: E. B. Mullings. Vacu- p. 23; Miscellaneous Transistors, pp. 23, 36; Part I; Dec. pp. Designing Your Own Amplifier: Norman H. Transistor Materials, p. 36; New Designs, pp. um -Tube Voltmeters, 55, Further Reading, p. 33-35; Basic DC VTVM, p. 33; Extending Crowhurst. Part I: Voltage Amplifier Stages; 36-37; 37. IIIa: Junction Range, pp. AC VTVM Circuit, Mar. 56, pp. 20-23, 43; Using Load Lines, Transistor Characteristics; Dec. 56, pp. 26-27, the 33-34; 32-33; The Collector Family, pp. 26-27, p. 34; Vacuum -Tube Ohmmeter, p. 34; Multi - pp. 20-21; Changing Circuit Values, p.. 21; 32; Purpose VTVM, p. 34; Instrument Accuracy, Frequency Response, pp. 21-22; Tube Manual Maximum Ratings, pp. 32-33. Operation, p. 35. Tables, pp. 22-23; Pentode Voltage Ampli- II , LISTENING TESTS úm Tú eontrolsVoltmeVoltmeters, 6 pp. fiers, pp. 23, 43; Triode or Pentode?, p. 43. Measurements, pp. 36- Part II: The Power Stage, Apr. 26-29; Power Supply 56, pp. 25-27, Listening For Quality: Joseph Marshall. Part I: 37; Circuit Measurements, pp. 27-28; Typical 4143; Plate Dissipation, pp. 25-26; Power Bass Response; Sept. 56, pp. 26-27, 43, 45, Measure- Output, p. 26; Distortion, pp. 26-27; Tetrodes Measurements, pp. 28-29; Other and Pentodes, 47; Introduction, p. 26; Frequency Response, ments, p. 29; Resistance Readings, p. 29. pp. 27, 41; Impedance Loads, pp. 26-27; Power Levels, p. 27; Bass Response, Vacuum-Tube Voltmeters, Part III; Feb. 56, pp. 4142. Part III: Phase Inverters; May 43, 45, 56, pp. 21-23, pp. 27, 47. Part II: Treble Response; pp. 30, 32, 41; Power -Supply Test, pp. 30-31; 4041; Series Transformer, Definition; Oct. - pp. 21-22; Parallel -Fed 56, pp. 24-26, 53, 55; AC Filament -Supply Test, p. 31; Voltage Transformer, p. 22; Treble Response, pp. 24-25; Distortion, p. Amplifier Stage, pp. 31-32; Power -Amplifier Split -Load Inverters, pp. 22-23; Paraphase pp. Inverter, p. 25; Definition, 25-26; Transient Re- Stage, pp. 32, 41. Audio Signal Generators, 23; The Floating Paraphase, pp. sponse; Stability, pp. 26, 53; Realism; Natural- Part I; June 56, pp. 20-22, 32-33. Audio 23, 40; Cathode -Coupled Inverter, pp. 40- ness. pp. 53, 55. Part II; Jul. pp. 24-25, 41; Output Impedances, p. 41. Part 1Va: Signal Generators, 56, Push 34. -Pull Power Stages; Jul. 56, pp. 19, MAINTENANCE 33-34; Composite Curves, pp. 33-34. Part IVb: Push -Pull Power Stages; Sept. 56, pp. Checking Your Tape Recorder: Herman Bur- THEORY 28-29. 37-38; Plate -to -Plate Load; pp. 28- stein; May 56, pp. 34-35, 3840. Speed Ac- Basic Electronics:' Roy F. Allison. I: Nature of 29; Operating Class, pp. 29, 37; Pentodes curacy, p. 34; Speed Stability, pp. 34-35; Dis- Electricity; Nov. 55, pp. 36-37, 39; Atomic in Push -Pull, pp. 37-38; Power Drive Stages, tortion, pp. 35, 38-39; Signal -to -Noise Ratio, Structure, pp. 36-37; Electric Charge, p. 37; p. 38. Part V: Feedback Amplifiers; Oct. 56, P. 39; Frequency Response, pp. 39-40. Conduction, pp. 37, 39. II: Volts and Am- pp. 27-30, 45; Output Stage, p. 27; Drive Sound Servicing: Irving M. Fried. Record peres; Dec. 55, pp. 38-40; Chemical Ioniza- Stage; Inner Loop, pp. 27-28; First Stage; Changers; Nov. 55, p. 14. Speed Troubles; tion, p. 39; Electric Cells, pp. 3940. III: Over -All Feedback, pp. 28-29; Low -Frequency Nov. 55, p. 14. Arm and Tracking Prob- Resistance; Jan. 56, pp. 30-32. IV: Power; Response of Inner Loop, pp. 29-30; High - lems; Nov. 55, pp. 14-15, 42, 44. About Series and Parallel Circuits; Feb. 56, pp

DECEMBER 1956 47 33-37; Power, p. 33; Resistive Circuits, pp. Amplifier Measurements, pp. 34, 42-43. Nature of Distortion, pp. 19-20; The Dis- 33-34; Resistances in Series, Pp. 34-35; Re- Distortion: Causes and Effects: Richard D. tortion Index; pp. 20, 34; The Tracking Equa- sistances in Parallel, pp. 35-36; Power Trans- Keller; Mar. 56, pp. 24-28. What Is Sound?, tion, p. 20. fer, pp. 36-37. V: Magnetic Effects; Mar. p. 24; Electronic Distortions, p. 25; Harmonic Music from Electrons: Robert Moog; June 56, 56, Pp. 38-40; Magnetism, pp. 38-39; Distortion, p. 25; Intermodulation Distortion, pp. 16, 18-19, 33. Pitch Control, pp. 16, Electromagnetism, pp. 3940. VI: Induc- pp. 25-26; Frequency Distortion, pp: 26-27; 18; Harmonic Generation, pp. 18-19; Volume tion; Apr. 56, pp. 36-38; Mutual Induc- Phase Distortion, p. 27; Transient Distortion, Control, pp. 19, 33. tion, p. 37; -Self-Induction, pp. 37-38. VII: pp. 27-28; Noise and Hum, p. 28.' Transistors in Audio Circuits: Paul Penfield, Jr. Capacitance; May 56, pp. 36-38. VIII: The Grounded Ear: Joseph Marshall. Equali- I: Transistor Action; Oct. 56, pp. 18-21, 42- Parallel and Series Reactances; June 56, pp. zation Curves; June 56, p. 5. The Slot 43; Introduction, p. 18; Transistor Materials, 30-32; Inductors in Series, p.. 30; Inductors Radiator; Jul. 56, p. 4. How Much Power?; pp. 18-20; Impurities, p. 20; Junctions and in Parallel, pp. 30-31; Capacitors in Series, Jul. 56, pp. 4-5, 37. Rectification, pp. 20-21; Junction Transistors, pP. 31-32; Capacitors in Parallel, p. 32. IX: Loudspeakers and Enclosures: George L. Aug- pp. 21, 42-43; Further Reading on Tran- Alternating Current; Jul. 56, pp. 30-31. Ef- spurger. I: General Loudspeaker Principles; sistor Action, p. 43. fective Value, p. 31. X: The Sine Wave; Aug. 56, pp. 16-18, 34. II: Electrical Re- Transistors in Transition: Paul Penfield, Jr.; Aug. 56, pp. 27-28, 37, 39; Rectangular Co- lationships; The Infinite Baffle; Sept. 56, pp. Apr. 56, pp. 16-18. Noise, p. 16; Imped- ordinates, p. 27; Trigonometric Functions, 22-24, 35-36; Impedance, pp. 22-23; Damp- ance, pp. 16-17; Biasing, p. 17; Frequency pp. 27-28; The Sine Wave, pp. 28, 37; ing, p. 23; The Infinite Baffle; pp. 23-24, Limitations, p. 17; Power Output, p. 17; Dis- Sine Wave Properties, pp. 37, 39. XI: In- 35-36. III: Resonant Enclosures; Oct. 56, pp. tortion, pp. 17-18; Miscellaneous Difficulties, ductance in AC Circuits; Oct. 56, pp. 34-35, 31-33, 47-48. IV: Horns and Horn Enclo- p. 18; Transistor Advantages, p. 18. 48.49. XII: Capacitance in AC Circuits; sures; Dec. 56, pp. 24-25, 3841; High - Why Equalize?: Herman Burstein; June 56, pp. Nov. 56, pp. 28-29, 4041. Frequency Horns, pp. 25, 38; Bass Horns, pp. 23-25, 37, 40. FM Equalization, p. 23; Disc The DB in Hi-Fi: Mannie Horowitz; Apr. 56, 3841. Record Equalization, pp. 24-25; Amplitude PP. 33-34, 4243. The Logarithm, p. 33; Minimizing Pickup Tracking Error: Dr. John D. Pickups, p. 25; Tape Recorders, pp. 25, 37. The Decibel, pp. 33-34; The Dbm, p. 34; Seagrave; Dec. 56, pp. 19-21, 34. The 40.

Index of Authors Audiocraft Magazine Vol. I, Nos. I - 14 Nov. 1955 - Dec. 1956 Dec. ALLISON, ROY F. FOWLER, CHARLES 56, pp. 4-5; Nov. 56, pp. 4-5, 44; 56, Kits. Mar. pp. pp. 4-5, 37. Basic Electronics. I: The Nature of Electricity; Construction of Modern 56, Listening for Quality. Part I: Bass Response; Nov. 55, pp. 36-37, 39. II: Volts and Am- 32-34, 41. Sept. 56, pp. 26-27, 43, 45, 47. Part II: peres; Dec. 55, pp. 3840. III: Resistance; FRIED, IRVING M. Treble Response; Definition; Oct. 56, pp. Jan. 56, pp. 30-32. W: Power; Series and Sound Servicing. Nov. 55, pp. 14-15, 42, 44; 24-26, 53, 55. Parallel Circuits; Feb. 56, pp. 33-37. V: Dec. 55, pp. 10, 4647; Jan. 56, p. 10; Practical Audio Design. Part I: Power Trans- Magnetic Effects; Mar. 56, pp. 38-40. VI: Feb. 56, pp. 10, 42; Mar. 56, p. 8; Apr. 56, formers and Rectifiers; Jan. 56, pp. 21-23, Induction; Apr. 56, pp. 36-38. VII: Capaci- p. 10; May 56, pp. 10-11; June 56 pp. 34-36. Part II: Power -Supply Filters; Feb. tance; May 56, pp. 36-38. VIII: Series and 10-11, 36; Jul. 56, pp. 10-11; Aug. 56, pp. 56, pp. 24-28. Part III: Decoupling Net Parallel Reactances; June 56, pp. 30-32. IX: 10-11; Sept. 56, pp. 12-13; Oct. 56, pp. 12, works and Voltage Regulation; Mar. 56, pp Alternating Current; Jul. 56, pp. 30-31. X: 55-56. 35-36, 4142. The Sine Wave; Aug 56, pp. 27-28, 37, 39. That Professional Look. Nov. 55, PP. 21-23. XI: Inductance in AC Circuits; Oct. 56, pp. GERACI, PHILIP S. 34-35, 48-49. XII: Capacitance in AC Cir- Rebuild Your Recorder. Nov. 56, pp. 18-21, MOOG, ROBERT cuits; Nov. 56, pp. 28-29, 4041. 37-39. Music from Electrons. June 56, pp. 16-19, 33. ALEXANDER, K. A. HAFLER, DAVID MULLINGS, E. B. The Village Soundsmith. June 56, p. 22. Modernize Your Williamson Amplifier. Jan. 56, Using Test Instruments. Vacuum-Tube Volt- pp. 16-18. meters, Part I: Dec. 55, pp. 33-35; Part II: AUGSPURGER, GEORGE L. Jan. 56, pp. 26-29; Part III: Feb. 56, Pp. Loudspeakers and Enclosures. Part I: General 30-32, 41. Audio Signal Generators, Part I: Loudspeaker Principles; Aug. 56, pp. 16-18, June 56, pp. 20-22, 32-33; Pan II: Jul. 56, 34-35. Part II: Electrical Relationships; The pp. 24-25, 34. Infinite Baffle; Sept. 56, pp. 22-24, 35-36. PENFIELD, PAUL, JR. Part III: Resonant Enclosures; Oct. 56, pp. 31-33, 47-48. Part IV: Horns and Horn Transistors in Audio Circuits. I: Transistor Enclosures; Dec. pp. 24-25, Action; Oct. 56, pp. 18-21, 4243. II: Mis- 56, 3841. cellaneous Transistor Types; Nov. 56, pp. SEEDER, LEE 22-23, 36-37. IIIa: Junction Transistor Hi Fi Pure and Simple. Aug. 56, pp. 22-23, 35. Characteristics; Dec. 56, pp. 26-27, 32-33. BOHN, WILLIAM C. Transistors in Transition. Apr. 56, pp. 16-18. Out of the Speaker into the Room. Nov. 55, RICHARDSON, J. E. pp. 24-25. . A Home-Built Pickup Arm. May 56, pp. 26-27, BOWE, GEORGE 40. Tips for the Woodcrafter. Basic Shop Tools; SAUNDERS, SCOTT J. Nov. 55, pp. 16, 4445. Using Hand Tools; Build in Your Hi-Fi. Mar. 56, pp. 16-19, 44. Dec. 55, pp. 8, 4546. Woodworking Draw- SCHOEDSACK, ERNEST B. ings; Jan. 56, pp. 8-9, 35. Joinery; Feb. Better Bass with Buster. May 56, pp. 28-31, 56, pp. 8-9, 3940. Plywood; Mar. 56, pp. 4142. 10-11, 4243. Regular Lumber; Apr. 56, HOKE, JOHN SEAGRAVE, DR. JOHN D. ºP. 8-9, 38-39. Wood Finishing; May 56, a Binding Tape Library. Dec. 55; pp. 36-37. Minimizing Pickup Tracking Error. Dec. 56, pp. pp. 8-9, 42. Basic Power Tools, Part I: HOLT, J. GORDON June 56, pp. 8-9, 35; Part II: Jul. 56, Pp. 19-21, 34. 8-9, 35; Part III: Aug. 56, pp. 8-9; Part IV: A High Quality Microphone Mixer. Dec. 55, pp. SOUTHWORTH, GLEN Sept. 56, pp. 10-11, 4042; Part V: Oct. 56, 24-27, 42. Chassis Layout and Wiring. Dec. 55, pp. 21-23, pp. 10-11, 44. Maintenance of Hand Tools; Microphone Roundup. Nov. 55, pp. 28-30. Tape News and Views. Nov. 12, 40; 43. Nov. 56, pp. 10-11, 13, 42. Sharpening 55, pp. Stereo Recording with a Pentron. Jan. 56, pp. Power Tools; Dec. 56, pp. 10-11, 43. Dec. 55, pp. 12-14, 48; Jan. 56, pp. 12-13, 38, 40; Feb. 56, pp. 12-14, 4041; Mar. 56, 19, 37-38. BURSTEIN, HERMAN pp. 12-13; Apr. 56, pp. 12-13, 4344; May Testing Without Instruments. Mar. 56, pp. Checking Your Tape Recorder. May 56, pp. 56, pp. 12-13, 45, 48; June 56, pp. 12-13, 29-31, 40. 34-35, 38-40. 33-35; Jul. 56, pp. 12-13, 39-40; Aug. 56, STERN, JOHN J., M.D. Multiple -Speaker Switching Systems. Feb. 56, pp. 12-13, 35, 37; Sept. 56, pp. 14-15, Build an AM Crystal Tuner. Dec. 56, pp. 16- pp. 22-23, 42. 4243; Oct. 56, pp. 14-15, 51, 53; Nov. 56, 18, 4344. Why Equalize? June 56, pp. 23-25, 37, 40. pp. 14, 4142; Dec. 56, pp. 14, 35-37. Optical Tape Timer. May 56, p. 35. CARINI, L. F. B. HOROWITZ, MANNIE TATUM, BROOKING FM Antenna Systems. Jul. 56, pp. 20-21, 35. The DB in Hi-Fi. Apr. 56, pp. 33-34, 42-43. Carnegie Hall on Wheels. Jan. 56, pp. 24-25, COHEN, ABRAHAM B. HUFF, JOHN J. 36. Making the University Classic. Feb. 56, pp. 16- TV Can Sound Better. Dec. 55. pp. 16-17, 43. TURNER, RUFUS P. 18, 37. KELLER, RICHARD D. Miniature Signal Injector. Jul. 56, pp. 2 2-23, CROWHURST, NORMAN H. Book Reviews. Nov. 56, p. 15; Dec. 56, pp. 37. Designing Your Own Amplifier. Part I: Voltage 29, 34-35. VAN SICKLE, HOWARD M. Amplifier Stages; Mar. 56, pp. 20-23. 43. Distortion: Causes and Effects. Mar. 56, pp. 24- A Stereo -Monaural Speaker System. Apr. 5 6, PP. Part II: The Power Stage; Apr. 56, 25-27, 28. 28-31, 4041. 4142. Part III: Phase Inverters; May 56, KLIPSCH, PAUL W. VILLCHUR, EDGAR pp. 21-23, 40-41. Pan IVa: Push -Pull Power M. Stages; Jul. 56, pp. 19, 33-34. Part IVb: Impedances in Multi-Speaker Systems. May 56, Speaker Enclosures: Types and Designs. Dec. Push -Pull Power Stages; Sept. 56, pp. 28-29, pp. 16-17, 4244. 56, pp. 18-20, 4041. 37-38. Part V: Feedback Amplifier Design; KRAMER, KARL WHITE, SAUL Oct. 56, pp. 27-30, 45. Building the Jensen Imperial. Nov. 55, pp. Speaker System Design Notes. Jan. 56, pp. 20, DARRELL, R. D. 18-20, 38-39. 34. Lebensraum for the Craftsman. Nov. 55; pp. 33, LAUER, JOHN E. WILLIAMS, S. R. 38. FM in Your Car. Nov. 55, pp. 31-32, 42. Turntable . . with Strings Attached. Dec. 55, Plain and Fancy. Feb. 56, pp. 19-21, 37. pp. 28-31. Sound Fanciers' LOWDERMILK, RONALD R. Guide. Jul. 56, pp. 26-27, 37, More Multi Than Most. Yours for the Making . Attractive Record 39; Aug. 56, pp. 29-31; Sept. 56, pp. 31-34; Apr. 56, pp. 22-24, 43. Storage Cabinet. Feb. 56, p. 29. JOSEPH Oct. 56, pp. 36-39, 44; Nov. 56, pp. 30-32, MARSHALL, WRIGHT, FRANK R. 34-35; Dec. 56, pp. 28, 4143. The Grounded Ear. Nov. 55, pp. 10, 40-42; You Can Build a Power Amplifier. Nov. 55, pp. DEVENDORF, D. L. Dec. 55, pp. 4-5, 43; Jan. 56, pp. 4, 32 - 26-27, 39. W-3 to Dyne II. Feb. 56, pp. 4-5, 41; Mar. 56, pp. 4-5 Sept. 56, pp. 25, 36-37. Apr. 56, pp. 4-5, 40; May 4-5, ZABRISKIE, ARTHUR I. DRAPKIN, 56, pp. 4445 HERBERT June 56, pp. 4-5, 36; Jul. 56, pp. 4-5, 37 Power Supply for the TV Sound Amplifier. Aug. The Soldering Story. Sept. 56, pp. 21, 39.40. Aug. 56, pp. 4-5; Sept. 56, pp. 4-5, 42; Oct. 56, pp. 24-26, 37.

48 AUDIOCRAFT MAGAZINE