The Straight 'N Pivoted
Dear Editor:
I would like to make a few comments regarding the controversy between pivoted and straight-line tonearms. The articles that appeared in the June 1980 and June 1983 issues of Audio were some of the better ones that I have read. I concur with most of what was written, but I would like to comment regarding the lack of skating (lateral) forces in linear-tracking tonearms. One thing usually overlooked in linear tracking turntables of the air-bearing type is the large tangential force that arises if the record hole is off center.
The effective lateral mass of such a tonearm is the mass of the arm itself, and will be several times the effective mass of pivoted or servo-assisted tonearms. Such a large effective mass being accelerated laterally could result in a lateral force on the stylus that is much larger than the skating force of a conventional tonearm. It would appear that any advantage of an air-bearing radial over conventional radials and ordinary tonearms is negligible under real world conditions. It is interesting to note that the lateral mass and the effective vertical mass differ in this design. In physics we would say this produces a coupled oscillator whose frequency and amplitude are a function of time, and, one has to wonder, what effect would this have on the system? It would seem that aside from the lack of a servo window, the air-bearing linear tonearm does not have any inherent advantages over the other design.
I also read with interest the letter contribution by Graeme F. Dennes that appeared in "Signals & Noise" in the May 1983 issue. I have spent a considerable amount of time researching the literature regarding tonearms and, after constructing several, have concluded that differences due to overhang, length, and offset angle in a well-made and reasonably mounted tonearm are very small and will probably be of little significance compared to factors over which the user has no control. As an example, the skating force is a function of complex factors, such as groove material and modulation. Also, many records have offset centers, and this causes the cartridge to be continually accelerated. This, in turn, requires the stylus to supply a counter force that will result in an unequal force on the groove walls. In regard to the selection of null radii (radii where the tracking error is zero), it has been said that one of these should be near the inner grooves since typically this is where the loudest passages are, but one's tolerance to distortion increases with increasing loudness, so maybe it doesn't matter very much.
Additional references are:
1. Olson, H. F., Modern Sound Reproduction, pg. 178. (This information is the same as Ref. 5 cited by Dennes.)
2. Guy, P. J., Disk Recording and Reproduction, pg. 96. (The denominator has a mistake in it.)
3. Gicca, Francis A., "Tonearm Tracking in Stereo," Electronics World, Oct. 1959, pg. 70. (Largely concerned with the effect tracking error has on crosstalk ratio.) George Shellenberger Assoc. Prof., Natural Sciences College of the Ozarks Clarksville, Ark.
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AUDIO ETC.??
Edward Tatnall Canby
(437 E. 11th Av., Eugene, OR 97401)
Dear AUDIO --
You are now observing my second letter on a genyooine Word Processor, a strictly pro model, the Osborne 1. The first letter was six lines long and took me two days. This one has taken about two weeks, what with accidental garblings, erasures and other dire mishaps. At this rate I figure I'll take about five years to do my first AUDIO copy, courtesy of the Osborne. It's all too zany. Like detaching pieces of words, which go scooting off on their own on the screen with me in hot pursuit: I never seem to catch up. Then, it is hard to understand that nothing here is always SOMETHING, that is, a space is a something and you have to treat it with respect because w it won't go away yyyyyy, and dreadful things hAPPen--
EEEEEEEEEE OOOOOOOOOPS
WAY
hey!!
It is always possible, if you are advanced enough in your thinking, to get track on the back. I mean back on the track, like this.
Then all goes very wellll11111, for awHILE. Auntil smthng else goes wrong, which doesn't take very long, alas, what with my fingers.
blurp URP ANYHOW, I'm taking advantage of the opportunity, until at least I have the basic concepts more or less under control and maybe can go on to a lot more, with my own machine???? Who knows I might even get a whole AUDIO ETC column processed before too long.
I've been staying on here in Eugene (OR) beyond the end of the Bach Festival to gather some highly interesting info on the Hult Center ,the latest in super-update concert halls, with THREE sound reinforcement systems including the fabulous 90-mike, 90-speaker AIRO. and ERES, as well as an update standard house system this is the first all-purpose center designed from the start for electronic sound assistance. I've heard a dozen or so concerts of all sorts, with reinforcement to match, and yesterday 1 was up on the catwalks hundreds of feet above the floor (!!) to look at the mikes, each in a Helmholz tube to resonate at a particular frequency... Will return to NYC July 11th and thence to Cornwall to finish writing something on all this heady stuff.
Yrs fr btr cmptrs, E.T.C,
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More on Tonearm Geometry
Dear Editor:
May I add another historical postscript to the comments on Tonearm Geometry by Graeme F. Dennes and B. V. Pisha found in the May 1983 "Signals & Noise" column? My father [Percy Wilson] had published his solution to the geometrical problem in 1924. However, though the use of an offset to reduce the tracking error was soon universally adopted in Europe, straight arms persisted in record players manufactured in America for many years. The first American references I have found were published in 1937. I should be interested to hear of any earlier ones.
Glover [1], then Chief Engineer of Shure Brothers, reported the work of one of his staff, Ben Bauer, who devised a needle tilt arrangement in a replacement cartridge for mounting in existing straight arms. Bird and Chorpening [2] of Astatic describe the problem, and a crystal pickup with an offset to reduce the error. Olney [3] discussed both record wear and distortion resulting from excessive tracking error, though not the geometry required to reduce the latter.
Ben Bauer also deserves credit for drawing attention to the distortion criterion in his 1945 article. I myself recently followed the trail back from there to Baerwald's 1941 paper (which I had to send for) and thence to Lofgren's 1937 paper (which I found in the Penn State library). The latter is in German, which I don't read easily, but it is interesting to note that he gives references to both British and American papers, including the 1924 paper by my father.
In conclusion, I would like to mention that the 1929 Wilson and Webb book, long out of print and hard to find in the original, is now available in reproduced form from University Microfilms, catalog number A000092.
-Geoffrey L. Wilson; State College, Penn.
References
1. Glover, Ralph P., "A Record-Saving Pickup," Electronics, Vol. 10, No. 2, Feb. 1937, pg. 31.
2. Bird, J. R. and C. M. Chorpening, "The Offset-Head Crystal Pickup," Radio Engineering, Vol. 17, No. 3, March 1937, pg. 16.
3. Olney, B., "Phonograph Pickup Tracking Error vs Distortion and Record Wear." Electronics, Vol. 10, No. 11, Nov. 1937, pg. 19.
Base to Computer
Dear Editor:
On pg. 37 of your November 1983 issue, Leonard Feldman says in "Computer-Aided Calculations" that base "e" logarithms are base 2.32059. This is wrong. Indeed, it would be inexcusable if most people did not already know that "e" is approximately 2.7182818.
-Alex Lewin; North Haven, Conn.
Author's Note:
I made a misstatement. The statement I meant to make was:
"The log (to the base 'e') of 10 is 2.30259." To put it another way, on pg. 37, the parenthetical notation (2.30259) should have come at the end of the paragraph in which it appears--instead of in the middle. Thus: "... it is necessary to divide the log expression in these equations by the natural log of 10 (2.30259)." Mr. Lewin is indeed correct, and everyone (including myself) does know that base "e" logs are to the base 2.7182818. However, rest assured that the misplaced parenthetical information in no way affects the actual computer program, which has been running successfully on my computer for many moons. So, no real harm done, except a pink-to-red coloration of my face....
-Leonard Feldman
And More Kudos, dbx
Dear Editor:
In view of Frank Wolfe's appreciative comment on dbx (Audio, "Signals & Noise," February 1983), let me add this fillip.
I'm a stereo repairman by trade, and when my older dbx 118 developed an intermittent problem, I opened it up, rather than shipping it back to dbx, to see what the matter might be. While the problem itself was easily traced to a broken solder joint and quickly repaired, I took time to note what good quality parts and workmanship went into this device. I'd known before that dbx used walnut panels for their cabinets made by handicapped workers, a friendly gesture, but I'd no idea of the quality they put between those panels.
The insides of my dbx look and feel like the best pro equipment I have worked with, and on. Kudos! Audio readers also might want to know that, as owner of dbx at the moment, BSR is able to offer dbx noise reduction in its cassette recorders, which cost surprisingly little and seem to work fine. This might be a good time to reevaluate BSR products and look seriously at what they're offering in the 1980s. I've taken a BSR cassette deck apart, and I can vouch for its quality innards. BSR changers have always been reliable low-fi performers, but now the company may be seeking serious higher aims. Based on their cassette deck, I think they may be on the right track. BSR, by the way, now incorporates both dbx and ADC under its brand name.
-George Androvette; San Leandro, Cal.
Editors Note: It's nice to know that you appreciate your dbx unit so much. Being a part. of the audio world by trade, your comments may carry a little more weigh: than the average audiophile's would.
-E.P.
Errata
In the construction article, "Drive Your Walkman 'Round the Block" (July 1983, cg. 70), the LM2931T adjustable regulator was incorrectly listed as being available from various electronics mail-older houses. The only sources for this regulator are National Semiconductor Corp. distributors listed in local Yellow Pages directories.
Figure 2 of M. J. Salvati's "Build a Center-Woofer Crossover" (August 1983) contains some errors. The pin numbers for the power-supply connections to the op-amps were accidentally omitted. The positive supply (+15 V) connects to pin 14 of each 4739; the negative supply (-15 V) connects to pin 7 of each. Also, pins 5 and 6 are reversed for each 4739. Pin assignments for the regulators (IC5 and IC6) were purposely omitted, as the pins of these ICs are not numbered in order. If you are unfamiliar with these ICs, consult a handbook or the pin diagram sometimes accompanying the IC. Also, both power-supply terminals were marked "-15 V"; the upper one should actually be the "+ 15 V" terminal.
(Source: Audio magazine, Jan. 1984)
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