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From: firstname.lastname@example.org (Alan Fowler)
Subject: Re: Acoustic Feedback reduction
Date: Mon, 13 Jan 2003 06:13:38 GMT
Organization: Whitethorn Software
NNTP-Posting-Date: Mon, 13 Jan 2003 05:09:02 +0000 (UTC)
X-Newsreader: Forte Agent 1.5/16.451
Spehro Pefhany wrote:
>Many years ago in good old _Wireless World_ (long before "wireless"
>acquired its present meaning(s)) there was a design published for a
>device used to allow higher volume levels in PA systems before
>feedback occurred (with a given microphone). IIRC, they used
>one or two multipliers in a circuit that shifted the audio pitch by
>Has this sort of thing been integrated into a single chip?
Not that I am aware of. What are you actually
trying to do - provide a higher sound level without
feedback? If so there are a number of options.
1. Use an electrical delay (adjustable) delay line to delay
a copy of the original sound by the time for the sound to
reach the microphone from the speaker(s) and feed it into
the amplifier in opposite phase and at a level to cancel the
2. use correctly designed and placed column speakers to
keep the level at the microphone low enough to prevent
3. Use a number of speakers along the length of the hall
with the appropriate electronic delay in the feed to each
speaker so that there are no obvious multiple sound sources.
I'm a bit rusty about the details, the last time I
did this was about 1954, in a hall with a reverberation time
o f ten seconds for a symphony orchestra with soloist. The
newspaper reports the next day said that both the orchestra
and soloists could be heard with great clarity throughout
Everyone was pleased.
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