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Thanks, but aren't we talking about two different things?

210.230.171.106

Posted by David Spear on August 7, 1999 at 19:23:41

In Reply to: Re: What about microphone diaphragms? posted by Charles on August 7, 1999 at 15:47:35:

Hi Charles,

Thanks for your detailed response, but aren't we really talking about two entirely different phenomena? In the classic Doppler effect, movement of the physical source of the sound causes frequency shifts, as in your piano sounding board analogy. However, once the sound waves are in the air, no further modulation takes place. (The low-frequency waves moving through the air cannot "push" the high-frequency waves, they simply interpenetrate each other.) Of course, superimposition of waveforms occurs, but the low-frequency waveforms do not cause the superimposed high-frequency waveforms to change in pitch.

I'm not saying that controlling the complex pattern of waveforms generated in the listening room is not of fundamental importance -- it obviously is, which is why proper speaker positioning and room treatments are so crucial in achieving good sound. And I agree with you that the ultimate goal of audio reproduction (i.e., to accurately reproduce the overall pattern of waveforms at the original performance) is impossible to reach, since every listening room has its own acoustic signature.

Given the above, I think that the best we can do is to work toward a reasonable compromise. In my experience, a realistic approach is as follows:

1) Design a listening space with appropriate dimensions to minimize reinforcement of standing waves in the bass.
2) Apply acoustic treatment (absorption and diffusion) to avoid excessive liveness or deadness.
3) Position the speakers carefully to minimize phase and echo effects and thus maximize imaging.
4) Use phase-coherent, panel-type speakers (ideally, one-way designs).
5) Listen in the near field.

I have found that employing the above approach results in a smooth frequency balance and an outstandingly deep and wide soundstage, which is the best that can be hoped for in a home audio system.

BTW, I agree with you that Kimber's use of the term "Doppler distortion" is rather misleading. In fact, since their method appears to involve increasing the amount of driver blending, it should actually increase Doppler effects. Maybe their idea is that the "Doppler distortion" exhibited by multi-way speakers is actually a loss of the Doppler modulation effects that should be present to accurately reproduce the recorded waveform.

Thanks again for your interesting response.

Good listening -- Dave

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