Focus is on loudspeakers for this issue and we usually publish a Directory listing the various models and specifications. However, this time we decided to use the space for articles on design and performance--particularly regarding the advantages and disadvantages of omni-directional sound propagation. Opinions differ widely--partly because of the compromises involved with the reproduction of stereo sound, partly because of limitations of loudspeakers themselves and partly because of indefinable personal preferences.
AM Hi Fi
Recently, a number of letters have been received extolling the virtues of AM and pleading for better AM receivers. AM is not inherently inferior to FM and there are several stations in the broadcast band radiating wide bandwidth, clean signals. But they are in a minority and the quality of most AM stations is incredibly bad.
It would be an over-simplification to say that the reason is a mercenary one but the desire to rope in the maximum number of listeners to hear the advertiser's message is certainly a factor. So all kinds of limiters, compressors and equalizers are used to get the loudest possible signal. It is also true that many station operators believe some signal processing is necessary because of the poor quality of many AM receivers--especially car radios. Some of the techniques were outlined by Irwin Fust, formerly Chief Engineer of several radio stations, in the November issue of Broadcast Management Engineering--known to its loyal readers as BME. Mr. Fust says, "It may be desirable to allow music to be broadcast with small limitations of dynamic range, but for most material some processing is necessary." After dealing with automatic gain control, asymmetric limiting and compression systems, Mr. Fust goes on to say, "Restricting the bandwidth of the transmitted signal will allow a considerable increase in the total audio power received by the listener while retaining the overall quality of the signal ... a high-pass filter cuts off any frequency below 100 Hz and a low-pass filter cuts off any frequency above 7.5 kHz. These filters are commercially available." Some equalizers peaking at 5 kHz and 300 Hz were described and then there was the following brainwave, "A little trick that can be done with some turntables it to increase the speed ever so slightly in order to give the recorded sound a `brighter' quality. Increasing the speed increases the pitch of the music and can produce a subliminal effect." Quite so, but the effect of all this processing is to alienate the music-lover and so there is no real demand for top-quality AM tuners or receivers. I have forgotten which prominent TV executive said, "The purpose of Television is to Sell," but AM radio reached that stage a long time ago ...
Men of Hi Fi
Looking at the Men of Hi-Fi transcript in the February issue, I suddenly thought, well, this is a nice photograph of Ray Dolby but I ought to have included one of Adrian Horne, so here it is. Adrian is Licensing Manager for the Dolby Company.
Setting the Record Straight
Percy Wilson's article on record care aroused a great deal of interest and we have been inundated with letters. One was received from Agnes Watts (widow of Cecil Watts) who says, "The Dust Bug was the first of our maintenance family of cleaners and it has never been claimed that this could deal with other than the dust in the groove being traversed by the Bug. Our Preener and Parastats were developed later and have been coping with dirty discs and maintaining clean ones successfully for many years. The disc washing machines on the market depend entirely on our Parastat brushes for their efficiency as no other brush has been manufactured with such delicate skill which enables the most stubborn dirt to be removed without damage."
-G. W. T.
(Source: Audio magazine.)
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