Dear Editor (Oct. 1981)

A President's Posture On Polypropylene

Dear Editor:

I read with special interest your interview with Mr. von Recklinghausen of KLH in the February issue.

I would like to amplify some facts concerning the introduction of polypropylene driver technology which may be of particular interest to your readers.

The use of polypropylene for loudspeaker diaphragms was patented by my colleagues and myself in 1976.

Twelve patents have been granted worldwide, including the United States (U.S. Patent #4,190,746) and Great Britain, and applications are in progress in a further 13 countries. It is felt by many acoustic engineers and that select group of "golden-ears," the mixdown staff in the BBC, that this technology represents a major advance in the state of the art.

Mr. von Recklinghausen of KLH and the engineers at Infinity and Peerless must be congratulated on their foresight in so wholeheartedly embracing this new technology, especially in a world confined by the traditional, conservative approach to audio. It is sanguine to note that by far the most dominant cone material used today is still paper (as described in the 1926 patent of Rice and Kellogg).

Most of the engineering fraternity would agree that a practical new cone technology is long overdue, and that polypropylene has an outstanding cost/ sound quality/ease of manufacture performance which shows signs of revolutionizing the future of moving-coil transducers.

Thank you for such a stimulating article on the problems of designing loudspeakers as expressed by Mr. von Recklinghausen.

-David W. Stebbings; President KM Laboratories, Inc.; New York, N.Y.

Going to the Source for "Stare"

Dear Editor:

As another Ken Nordine fanatic, I highly commend Michael Tearson's review of Stare with Your Ears. I haven't heard it yet, but I'm sure it's amazing.

When I had no luck finding it around here, I called Snail Records in Chicago.

After asking the receptionist many questions, she offered to put Ken on the phone since he was right there. I was awed--it was the voice on the phone! This was perhaps better than meeting him in person.

Anyway, he commented that Snail's distribution is very small. Therefore, thought you might want to print Snail's address so that readers can mail-order the album. Send $7.00 for the album to: Snail Records, 6106 North Kenmore, Chicago, Ill. 60660.

-Fred Dalrymple; Princeton, N.J.

Leach Pre-Preamp Update

Dear Editor:

The pre-preamp construction project I presented in Audio's February 1978 issue can be updated by changing R1 to 39 ohms, R2 and R5 to 5.1 kilohms each, R3 and R4 to 15 kilohms each, C1 to a 0.1-µF polyester cap, C3 and C4 to 100-pF silver mica or polystyrene caps, and C2 and C5 to 220-µF, 10-V electrolytic caps. In addition, two 150-ohm resistors should be added--one in series with the emitter of Q1 and one in series with the emitter of Q2. (The emitter leads have the arrow.) Finally, C8 should be omitted. For minimum hum, the signal ground for each channel should be kept isolated from the other channel and from chassis ground. The input impedance is calculated as R1 in parallel with 133.5 ohms. With R1 = 39 ohms, it is 30 ohms. The value of R1 can be changed to change the input impedance if desired.

-W. Marshall Leach, Jr.; Atlanta, Ga.

Super Featherweights

Dear Editor:

I've just received my May issue of Audio Magazine, and, to my delight, found an article on "The New Featherweight Headphones." Having seen various lightweight headphones in Audio and other hi-fi magazines, as well as various reviews on them, I don't remember ever coming across one with separate left and right volume controls.

It would seem to me that such controls could be added without adding significantly to the price or the weight of such headphones. I hope some of the top brass of the audio companies read this and keep the idea in mind, as I'm sure that others besides myself would find these new lightweight phones even more attractive with the added convenience of volume controls.

-Dwight Gaines; Cleveland, Ohio

Missing "Data"

Dear Editor:

A few months ago I saw the column "All That Data." The explanations were excellent and immensely improved my enjoyment of your magazine. Previously I understood parts of what you were saying but not all. My belief is that I and many amateur audio buffs would be thrilled if there was a whole special issue of "All That Data," separate from your regular monthly issues, available to subscribers.

The latest issues have not included the "All That Data" column. I would really appreciate knowing what has happened to it.

-Michael D. Laganella, M.A. Cinnaminson, N.J.

The Editor Replies:

The reason we haven't published more "All That Data" columns is that Mr. Laganella's letter is the sum total of the response we've received. We will continue it if readers want it, but so far it appears that other materials should be featured.

Addenda: Pioneer F-9 Tuner Some important test results were omitted from our August 1981 review of Pioneer's F-9 tuner, and we present them here. The IHF mono sensitivity was 11.2 dBf (2.0 µV), stereo sensitivity 25 dBf (9.8 µV), the 50-dB quieting in mono was 15 dBf (3.0 µV), the 50-dB quieting in stereo was 35.6 dBf (33.0 µV), and, finally, the capture ratio was 1 .0 dB in the narrow i.f. position and 2.7 dB in the wide position. We apologize to our readers for this oversight and thank Mr. Robert Moore of Atlanta, Ga., for calling it to our attention.

Erratum:

How Impedant, Two A typo was smuggled by a Maxwell's Demon into the item entitled "How Impedant of You" in the "Audioclinic" column on page 14 of the May 1981 issue.

The impedance of three 8-ohm speakers in parallel is 2.66, rather than 3.66 as was stated in the item; the method of calculation shown further on is correct.

Our apologies.

(Source: Audio magazine, Oct. 1981 )

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