Box 392: Letters to the Editor (Vol.2, No.1: Winter/Spring 1979)

To make room in this issue for the voluminous transcript of our State of the Art seminar, we're cut ting back the space allotted to a number of our features, including this column. (How much small print can we run, after all?) That means we're publishing only those letters this time that demand immediate attention in our judgment, saving others of “evergreen” subject matter for future use. As a matter of policy, any letter of general interest or specific concern to our subscribers (rather than just to the letter writer) stands a good chance of being printed here; letters may or may not be excerpted at the discretion of the Editor. Ellipsis (. . .) indicates omission. Address all editorial correspondence to:

The Editor, The Audio Critic, Box 392, Bronxville, New York 10708.

First, the letters on what currently appears to be the premier subject of our editorial correspondence, phono tracking alignment.

The Audio Critic:

Being avid readers of your esteemed publication, we would like your readers to be told of a European pioneer in the field of lateral tracking geometry. The mathematical proof of the distortion effects of lateral tracking error is 40 years old rather than 37 years. Erik Lofgren published his first paper on this subject as early as 1929 in the Swedish journal Radio.

We enclose a copy of Professor Erik Lofgren's German-language paper in the then-young Akustische Zeitschrift, Nov. 1938-three years prior to Mr. Baerwald's paper. We have attempted an English summary which we hope you will publish.

Many thanks for Part III with the excellent alignment instructions! Do keep on spreading the light! Yours sincerely, Sven Eriksson Lars Backlund Ingenjorsfirma Sven Eriksson Johanneshov, Sweden Yes, indeed: had no other paper been published on the subject of lateral tracking error after Lofgren's, tone arm designers would still not be without a mathematical model for specifying effective arm length, offset angle and over hang correctly, although the specified values would differ by trivial amounts from those dictated by the Baerwald criteria. Therefore, in that sense, it's true that Lofgren beat Baerwald to the punch by three years.

It must be pointed out, however, that Baerwald was totally conversant with the Lofgren paper and gave it full credit, while arguing that his definition of minimum distortion over the recorded area of the disc was preferable to Lofgren's and that his use of the Chebyshev approximation to calculate correct tone arm design parameters was some what superior to the method of least squares suggested by Lofgren. Further more, the Baerwald paper is by far the more comprehensive and profound of the two; for one thing, it spells out more clearly and emphatically the crux of the matter: that tracking error generates FM distortion, which is more annoying than ordinary harmonic distortion.

Since we never published a summary of Baerwald, we don't see a compelling reason for publishing a summary of Lofgren, either, but we certainly appreciate having the full text of the original 1938 paper in German through the courtesy of our Swedish friends. Whether the original insights came from Stockholm or Cleveland, Tokyo has certainly had enough time by now to heed them. Thank you, Messrs. Eriksson and Backlund, for understanding and caring.

-Ed.

The Audio Critic:

I would be very interested to know what the tracking error is at the extreme outer groove corresponding to your Optimum Overhang and Offset Angle Chart? . ..

Sincerely, G. Bearman

Chairman & Managing Director Mayware Ltd. (Formula 4), England

The absolute value of the tracking error would depend on the effective arm length: the longer the arm, the smaller the tracking error. The question, how ever, is essentially irrelevant; as we've pointed out many times before, it isn't the tracking error that must be minimized but the ratio of the tracking error to the radius at which is occurs. That's what Lofgren, Baerwald, Seagrave, etc.

are all about. Thus the tracking error is inevitably largest at the outermost groove, and that's the way it has to be.

If this query has anything to do with the Formula 4 Mk III tone arm, we must add that its offset angle is slightly incorrect and its specified overhang more than slightly so. An arm with an effective length of 229 mm should have an offset angle of 24° 5° (not 23° 40') and should be mounted with an overhang of 18.1 mm (not 20 mm) if it is indeed optimized for a 12-inch LP disc as the Formula 4 is claimed to be. Furthermore, the inner zero-tracking-error point should be at a radius of 66.04 mm (in stead of 63.50 mm). Not as a matter of opinion but in accordance with natural law. (Our apologies if we misinterpreted the intent of the question.)

-Ed.

The Audio Critic:

Enclosed is some material by Percy Wilson on VTA and elliptical versus spherical styli that may interest you, if you have not seen it already.

In the June 1964 Gramophone Wilson puts his finger on a difficulty with any attempt to adjust the VTA: tilting the cartridge or arm to correct the VTA also tilts the stylus away from perpendicular, so that the stylus no longer fits the record groove. The line contact of the new stylus shapes would thereby be up set. Until the VTA is standardized there would appear to be no fully satisfactory solution...

Sincerely yours, F. Brock Fuller

California Institute of Technology, Pasadena, CA

Your letter arrived very shortly after we had started to worry about the same thing ourselves. You're undeniably right, and our current thoughts on the subject are written up in the preamble to the cartridge and turntable reviews in this issue. Meanwhile it turns out that Mitch Cotter has also been wrestling with the problem; he has outlined to us a solution so radically original, complex and daring that we feel quite in competent to comment on it at this point.

We'll believe it when we see it. To us simple folks, a stringent VTA standard appears to be the shortest possible route to satisfaction, at least as far as future records are concerned. Since the number of decision makers on the record cutting side of the phono industry isn't all that large, we can't see why at least a cutting standard should be a major ‘techno political’ problem. The pickup manufacturers could then comply with the standard or not, as the market demands.

-Ed.

The Audio Critic:

In your Spring through Fall 1978 is sue you published my letter to Mr. Bill Carter of Australia, which he submitted to obtain your response to my views on lateral tracking error in pickups. You kindly printed my whole argument, but proceeded not-so-kindly to dismiss it as 'casually condescending speculation' which ignored the investigations of Baerwald and others. Now I am aware of the papers to which you refer, and of the fact that some aspects of tracing distortion may be regarded as equivalent to a form of frequency modulation. (Doppler distortion in loudspeakers is an other example of this interchangeable viewpoint, where time-displacement side bands closely resemble ordinary IM products.) The reference in my letter to time errors between the two groove walls was not made in ignorance of the Cooper/Woodward theses, but in simple response to your own argument on the matter, spanning pages 52/53 of your July September 1977 issue. Perhaps it was not your intention, but the wording there seems to imply that the 'time smear' of 12.5 uS with which you were concerned involved the strictly stereo aspect of the signal. You stated that it 'can blur the focus of a stereo signal to some extent. (This is not an unreasonable figure to assume.) My reaction was to this simple point. I argued to Mr. Carter--and stick to my guns-that the suggestion as put is unreasonable. A phase error between channels corresponding to such a minute time difference would not blur the focus of a stereo signal. I readily accept that I misconstrued your comments, and that my rewording of your explanation must have seemed puzzling, but I humbly suggest that the initial fault was in your own misleading use of words. I know from bitter editorial experience how easy it is to say or imply the wrong thing, and I see that even in the disputed letter I referred at one point to the 'two grooves' instead of the 'two groove walls'. We must all try to be more careful.

Yours faithfully, John Crabbe, Editor, Hi-Fi News & Record Review, Croydon, England

Agreed. We must all try to be more careful. We'd be the last to claim that our writing is so simple and lucid that further editorial effort couldn't make it simpler and more lucid yet. But as we depart uttering these humilities, we're strongly tempted to turn around in the doorway, like Peter Falk doing one of those delayed exits in the Columbo series, diffidently raise our right hand, and say, ‘Just one more thing ..’ Just one more thing, Mr. Crabbe.

Didn't you write in your letter to Bill Carter that the audibility of tracking angle error is in your opinion due to “'old fashioned harmonic or IM distortion'? Old-fashioned, right? Would a person whose perception of the subject is in formed by the Baerwald, Bauer, Wood ward and Cooper analyses use that word? Are time-dispersive auto-modulations of the signal the same as good old THD and IM? Oh, I see. Just another little carelessness in the use of words. Well, thank you very much, sir. I'd better be going now . ..

We're inclined to believe that Columbo would arrest Mr. Crabbe the very next morning for intellectual weaseling in the first degree. But until a fair trial, the Anglo-Saxon presumption of innocence must apply.

-Ed.

And now, just a few more letters in the miscellaneous category.

The Audio Critic:

I have noticed that among all the amplifiers and preamplifiers that you have tested, you have never mentioned McIntosh, even though this is one of the most widely known and sold brands. Did you have a particular reason for this? Is the equipment so bad that it does not even warrant a mention? Or are audiophiles just biased against Mac?

Sincerely yours, Lester F. Keene, Cocoa, FL

McIntosh established its original reputation with outstanding vacuum tube equipment back in the late forties and early fifties, plus superb dealer relations over the years and the merchandising attitude that the customer is al ways right. Such a solid foundation is virtually unshakable in the marketplace, even after years and years of engineering mediocrity. We don't know of a single SOTA-oriented audio professional, how ever, who believes that McIntosh is in the forefront of the purist /perfectionist sec tor today-or was even a decade ago.

Unfortunately, to prove this with our own laboratory and listening tests, we'd have to purchase the equipment, since McIntosh doesn't believe in lending stuff to noncommercial reviewers. And if we bought it, we wouldn't know where to sell it after the tests. In the audio circles where we move, nobody wants it or even knows anyone who might.

-Ed.

The Audio Critic:

Thank you for reviewing our 10/24 subwoofer. The following may be of value to interested readers:

(1) We have no dealers. For in formation please write The Bass Mint, Box 153, Powell, OH 43065. SASE's are very much appreciated.

(2) The price of the 10/24 is $250 apiece, $475/pair, plus shipping. Ship ping charges are not refundable under the terms of our 30-day trial period.

(3) We will not make specific brand recommendations on Crossovers, power amps, or speakers to go with the 10/24.

That is the province of The Audio Critic and other magazines. We do recommend low-level 'electronic crossovers and separate bass amplification (as opposed to high-level passive devices), subsonic filters, and good turntable isolation.

(4) We have no phone listing at this time. Due to our limited manpower we just can't afford to be on the phone all the time. Callers trying to reach me at home will encounter my answering de vice. Please write.

Thank you.

Sincerely, Ed Cottle

President and Stock Boy

The Bass Mint

Powell, OH

Maybe that's why your subwoofer is correctly aligned and so many others aren't. While you're doing your engineering homework, those other de signers are busy gabbing on the phone.

-Ed.

The Audio Critic:

I am pleased with your evaluation of the sonic virtues of the H-3aa power amplifier but do take exception to two of your assertions.

1. The power tubes I use (6LF6) are being manufactured in the USA by GE and Sylvania. They are also being made in Japan and Yugoslavia. I have been informed that they will be around for many years. In your Vol. 1, No. 3 issue, page 4, you wrote that the Berning hybrid tube amplifier using 6LF6 tubes will be manufactured by Audionics. Also please note: The Acoustat X ($2200) uses 6HBS5 tubes, which is also a TV tube.

This tube was used in my H-3 stereo amplifier in the 1960's. The Beveridge 2SW-1 ($7000) uses 40K D6 tubes, also a TV tube. My point is that these two types are of even older vintage than the 6LF6 tube, yet you did not caution a buyer of the Beveridge system about their not being able to obtain them in a few years. I am sure if tubes do a better job in an amp or preamp they will always be available from one source or another.

Before taking up the second subject that makes me unhappy I would like to digress for a minute, if I may. Before transistor amplifiers the rated impedance of most high fidelity speakers was 16 ohms. In Britain practically all speakers were 15 ohms. There were sound reasons for this as, all other things being equal, a higher impedance speaker is more efficient and the crossover design is not as complex. We are refer ring, of course, to moving-coil speakers.

Electrostatic speakers are inherently of high impedance and this is lowered by means of a transformer. The Acoustat and Beveridge speakers use a different approach. They do not use a trans former; instead they employ very high voltage amplifiers to drive the speakers directly. The KLH-9, Quad, and Koss are examples of speakers using trans formers. In general, the lower the turns ratio of the transformer the better the speaker because of tighter coupling and other factors that I will not go into here. The KLH-9 impedance is 16 ohms, the Quad 15 ohms and the Koss 4 ohms. The KLH-9 and Quad were de signed for tube amplifiers, the Koss for solid state.

The reason for the lower impedance of speakers today is, of course, the fact that transistor amplifiers, being voltage limited, provide more power for such speakers. As an interesting aside you implied in your review of the Tangent RS2 (Vol. 1, No. 5, page 25) that it was an inefficient speaker as you were able to make the Levinson ML-2 clip on it with a master tape of piano music. On the other hand, I can make the Tangent RS2 play very loud with the H-3aa. The reason for this is simple:

The impedance of the RS2 at 70 Hz, for example, is 11.5 ohms; at 500 to 2000 Hz it is 9 ohms, and it rises steadily to over 20 ohms at 6 kHz, which is well above the fundamental tones of the piano. With the ML-2's 14 volt maxi mum voltage rating you can see that there is very little power to drive the Tangent. End of digression.

2. Many audiophiles are using the H-3a and H-3aa with electrostatic speakers such as the KLH-9's that keep their impedance high up into the upper range and also with the Quad, which does fall to low values but nonetheless sounds extremely good. For owners of double Quads I recommend wiring them in series and, if I may be allowed to boast a little, they do sound fantastic.

Thank you for allowing me to comment.

Sincerely yours, Julius Futterman, Futterman Electronics Lab, New York, NY

It was unquestionably a miscarriage of justice that your amplifier was singled out for our general caveat about the future of vacuum-tube audio equipment.

What's true of one particular design is true of them all: their longevity depends on the TV replacement market, the Russian aerospace industry and other factors outside the world of audio. We seriously doubt whether audio manufacturers by themselves could keep even a single vacuum tube factory in business through the 1980's. On the other hand, you may be quite right insofar as these other demands may preserve vacuum tubes from extinction for decades to come. Your guess is as good as ours or anyone else's.

The rest of your comments all point to an implicit conclusion we have shared for quite some time, namely that the power amplifier and the loudspeaker should be conceived and designed as a single system, the “back end” of the audio chain, not as two separate all purpose modules that never quite mate optimally. The trouble is that very few audio designers have an equal mastery of both disciplines. For example, neither the Acoustat nor the Beveridge amplifier is as highly refined as yours, although their philosophy of integrated design is certainly valid.

-Ed.

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[adapted from TAC]

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Records & Recording

Various audio and high-fidelity magazines