Dear Editor (Oct. 1970)

Eccentricity

I was glad to see the subject of poor record pressings taken up in your column for July, because the scratched and dirty condition of many of the records I obtain from domestic sources has led me over the last several years to import most of my purchases from England, Germany, and Japan.

If the difficulty with off-center records were due to an off-center hole, as your correspondent complains, both sides of the record would be off in the same direction and of course by the same amount; this has almost never been my experience, and I am plagued by records well enough centered on one side only.

How much eccentricity ought to be tolerated? It is easy to show (and easier to hear) that the effect on the pitch of the music is greatest at the end of a side, where the radius is at least 60 mm. Nowadays a turntable wow specification of 0.1% is respectable, and applying this as a standard would require records to be no more than 0.06 mm. off.

A record off by this amount will cause the pickup arm to oscillate over a distance of 0.12 mm. as the record rotates, and this is about the smallest motion which can be measured easily on fine pitch recordings. In my collection the records which meet this standard are the older ones and those made in Germany, with those made in England running a close second.

Which turntable manufacturer will be the first to provide a conveniently adjustable eccentric spindle?

-J. D. REED, Chicago

Eccentricity used to be more prevalent in England, but seriously, the problem lies with the record manufacturers and it should not be passed to the record player designers for a solution.

-ED.

Integrity

In the midst of all the electronic marvels of today and tomorrow at the EIA/Consumer Electronics Show, it was an unexpected pleasure to see that at JBL they still care about the guy who bought last year's model. Their new tuner will have interchangeable fronts, one of which will match their discontinued SA 600 integrated amp. That's a kind of integrity consumers seldom see. I appreciate it, JBL, I'll bet others do too.

--DAVID S. MONETT, Elmhurst, N.Y.

To JBL's President, Arnold Wolf--take a bow...

More on Doppler

I found the article on Doppler distortion by Roy Childs very interesting indeed. Little has been published on this subject-most experts apparently taking the view that Doppler distortion does not exist, or if it does, it is not significant.

As far as I know, Paul Klipsch is the only one who has really investigated the problem, but unfortunately his articles in the AES Journal and elsewhere are spoiled by his `blowing the trumpet' for horn systems. Perhaps you can persuade him to write a factual article without the propaganda?

--James Russell, Bridgeport, Conn.

Well, we did manage to persuade Paul to write an article for us although I must admit, the faint but persistent sound of a trumpet can be heard in the background! Years ago, most experts did tend to disregard the Doppler effect. The late Henry Hartley, one of the early pioneers said in a letter to me in 1961, "1 had a magnet design which avoided cross-modulation, mistakenly called the Doppler effect." He did in fact carry out a series of experiments which proved that certain spurious combination tones were caused by nonlinear voice-coil excursions relative to the magnetic field. The present interest in Doppler distortion--or as Paul has it, modulation distortion-is due to the advent of bookshelf speaker systems using small speakers which necessarily have large-amplitude cone movements to produce a reasonable base.

-ED.

(Source: Audio magazine.)

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