SIGNALS & NOISE (Letters to Editor) (Dec. 1990)

Twin Tweaks

Dear Editor:

I read the review of the Lirpa Labs VCDRS CD player (April) with great interest. My work on similar devices leads me to offer, with all due respect, suggestions for two modifications that should be helpful in suitably furthering the development of this equipment:

The problem with rumble will be cured only to a limited extent by scanner tire and suspension refinements.

One of the other contributors to the problem is flexing of the scanner control line. This can be greatly improved by making the line of hollow tube filled with heavy, silicone damping fluid. I believe the Swiss are a likely source for this tube.

The major contributor to the troublesome rumble, however, is Doppler modulation of the r.f. signal from the scanner to the pickup antenna that is on the control unit. As the scanner rotates, the r.f. signal will be modulated at rates varying from 8.333 Hz when the scanner is at the outside track of the CD (500 rpm) to 3.333 Hz at the inside track (200 rpm). Assuming that the patents on the Leslie Tone Chamber rotating speaker assembly have expired, the VCDRS Doppler problem can be solved by mounting the control unit's pickup dish on a turntable synchronized to the CD turntable.

With the above improvements, the VCDRS should be everything that is expected of it. By the way, I am offering a useful accessory for the VCDRS, a small light that mounts on the base of the scanner assembly and shines up to illuminate the label on the CD. The power for this light will be supplied by a modification that makes the scanner r.f. link a duplex channel, thereby eliminating the need for wires. Prices on request, providing the people in the white coats will let me receive mail.

-Norman S. Cromwell; Al. Llihneerg 8472 Lynchburg, Va.

Reception Perceptions

Dear Editor:

I read with interest the "Auricle" review of the AudioPrism 7500 indoor FM antenna (December 1989). Reading this review reminded me that I do not ever recall seeing a review of a real outdoor FM antenna. While products such as the 7500 may be useful, those of us who live more than a few miles from a major city need a real outdoor antenna, probably mounted on a tower. In my case, I listen to two public radio stations. One is a 10-kW station, and the other is 2,500 watts. Both are located about 45 air miles away. Obviously, a component like the Audio-Prism is inadequate for many of us outside a major metropolitan area.

I rely on my amateur-radio friends for antenna information. In many cases, this technology is not directly transfer able, as there are significantly different technical considerations for transmit ting antennas.

There are many sources of high-gain antennas. Please consider reviewing this often overlooked component.

-W. Lloyd Piper Kokomo, Ind.

Editor's Reply:

Actually, it has been quite some time since we did a test of a true outdoor antenna, but--thank goodness!--some things, like the laws of physics, don't change. Thus, a four part article by M. J. Salvati on antennas seems to be what Mr. Piper, and perhaps other FM devotees in the fringe areas, needs. This article appeared in our January through April 1978 issues. Salvati also wrote a book on this subject, which still seems one of the very best of its kind: TV Antennas and Signal Distribution Systems (Sams 21584). I believe that the book is out of print, but you may be able to find it in a library or a used book shop. Incidentally, the AudioPrism antenna really ought to work reasonably well at 45 miles.

-E.P.

Wood-Affected

Dear Editor:

With regard to Kurt Staiger's letter published in the March 1990 issue, I believe recognition of correct absolute polarity is definitely a learned skill, just like learning to listen to classical music in junior high school.

Last fall, I purchased a well-known $3,300 D/A converter which happens to have an absolute phase switch. The manufacturer stated that with proper phase orientation, "the better defined, more energetic bass and more stable imaging will be obvious." However, I couldn't find anything consistent to determine the proper setting and generally left it on 0°.

Then I obtained a copy of R. C. Johnsen's The Wood Effect, and read it very carefully. One important point the author brought out was that you will not hear absolute phase effects from speaker systems that have multiple 12-dB/octave crossovers because the phase structure of transients simply isn't preserved in such systems. Electrostatics or ribbons are best, but a dynamic system with 6-dB/octave crossovers, as is the case with the units I am using, should also be phase coherent.

Johnsen provides a short list of recordings that he has identified as being 180° out of phase. I already possessed three of these, and played them several times over my system with the phase knowingly correct and incorrect. I finally began to perceive what Johnsen was talking about. For someone without a phase-reversal switch, the new Chesky test record is invaluable (Jazz Sampler and Audiophile Test Compact Disc, Volume I, JD37). It contains a trumpet solo, re corded first in phase and then out of phase. I should think anyone could hear the deleterious effect on the tapped or brushed cymbals by being played out of phase. I highly recommend this disc to Kurt Staiger.

I now know what to listen for in recordings I suspect might be 180° off. Organ recordings are particularly easy to evaluate: Does the "chirp" of the organ pipe appear at the same time and place as the voice of the pipe? A singer's sibilants are another giveaway.

-Bernard A. Engholm; Carlsbad, Cal.

Grateful for Johnson

Dear Editor:

The intent of this letter is to express my sincerest appreciation to Michael Wright and your staff for your excellent review of Eric Johnson's Ah Via Music (August). I listen to many styles of music, classical included, and I have many favorite musicians. Eric Johnson, however, is one of those whose music has touched my heart and soul like no other. His attitude about life and music sets a tremendous example for musicians everywhere. This is rock music for the most part, and this album is a testament to those "golden-ears" that rock 'n' roll should stay firmly in place in the world of audiophiles. Eric's display of talent on this record is surpassed only by his performance on stage. He is truly deserving of success. Thanks again for helping to spread the word.

-Albert Madariaga; Dallas, Tex.

Erratum

The address of Terk Technologies, whose Pie FM antenna was reviewed in the November issue, is: 233-8 Robbins La., Syosset, N.Y. 11791.

(Source: Audio magazine, Dec. 1990)

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