Re: Real Instruments Sound Better
By Robbie Rhodes
Referring to the article in digest 951116 by Richard Weisenberger (forwarded from piporg-l group) --
If a side-by-side comparison concert were to be arranged the electronic organ, with it's audible distortion, would be noticeably inferior. (Fortunately for churches and manufacturers, such comparison situations are rare.)
The knotty problem in high-power audio systems remains in the loudspeakers: they are still the main cause of intermodulation distortion. At low power levels one can get a pretty clean sound nowadays from the variety of consumer loudspeakers. It's fun to compare them in a hi-fi shop, while playing your own favorite (hence well-known) piano CD.
A thoughtful old-timer engineer explained why multiple-port speakers (with woofer, squawker & tweeter) were developed:
"Imagine that you are hearing two adjacent loudspeakers. One (the woofer) radiates a low frequency sine wave and the other (the tweeter) a high frequency sine wave, at equal sound pressure [equal perceived intensity]. Both radiators are stationary except for the sine wave motion of the loudspeaker cone.
"Now imagine that the two sine wave signals have been combined, to radiate from only one loudspeaker. Low frequencies demand long excursions of the cone, but the high frequency barely wiggles it. This is equivalent to attaching the high-frequency tweeter to the _cone_ of the woofer, and the result is that the high-frequency sine wave is frequency modulated by the low-frequency motion of the woofer. It's a simple Doppler effect."
And the result is a multitude of new, unwanted frequencies, clustered about the high frequency sine wave. This is called intermodulation (IM) distortion, and it can be _very_ unpleasant. Remember, in the 50's, how the finest of the high fidelity phonographs were demonstrated using recorded bells? The ear is very discerning about these familiar percussion sounds, and the smallest IM distortion in the system becomes a literal pain-in-the-ear!
One realization of the "ideal loudspeaker" might be a disk or a cone, such that the active ring of vibration moves inward with increasing frequency, thus precluding Doppler modulation of the high frequencies by the lows. If this approach were feasible we wouldn't need loudspeaker arrays. ...
-- Robbie Rhodes
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(Message sent Wed 22 Nov 1995, 06:35:30 GMT, from time zone GMT-0800.) |
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