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From: Don Pearce
Subject: Re: Acoustic Feedback reduction
Date: Mon, 13 Jan 2003 22:24:46 +0000
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On Mon, 13 Jan 2003 19:18:10 +0000, John Woodgate
>I read in sci.electronics.design that Don Pearce
>wrote (in <firstname.lastname@example.org>) about 'Acoustic
>Feedback reduction', on Mon, 13 Jan 2003:
>>To get standing waves you need the organisation supplied by flat
>>surfaces facing each other. With rough curved surfaces such as you
>>find in caves, the reflections are diffuse, with none of the
>>phase-coherence you need to set up a standing wave. Provided too much
>>energy is not absorbed at each reflection, you still get the
>>reverberation time - but no standing wave.
>OK, I now understand why you think that, but I'm sure it is not true. A
>curved surface that is not too rough compared with the wavelength of the
>sound acts as a curved mirror. Certainly the walls of most of
>Chislehurst caves have been smoothed by occupants over about 2000 years,
>and the side walls are substantially vertical and parallel in many
>places. Plenty of scope for standing-wave generation there.
Don't think I actually named Chiselhurst. I was simply using the cave
scenario to point out that standing waves rely on smooth surfaces -
they are if you like a subset of reverberant spaces. Good studios
break up flat walls in order to minimise the problem of standing
waves. There is nothing inherent in a reverberant space that forces it
to produce standing waves.
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