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From: firstname.lastname@example.org (Nico Coesel)
Subject: Re: Acoustic Feedback reduction
Date: Sat, 11 Jan 2003 14:42:45 GMT
NNTP-Posting-Date: 11 Jan 2003 14:42:29 GMT
X-Newsreader: Forte Free Agent 1.21/32.243
>"Nico Coesel" wrote in message
>> "g0mem" wrote:
>> >"Spehro Pefhany" wrote in message
>> >> 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
>> >> around 10Hz.
>> >> Has this sort of thing been integrated into a single chip?
>> >I never come accross that method before but there is no reason why it
>> >shouln't work. Another technique to cure feedback on a PA system is to
>> >graphic equalizer. The method is to turn the volume up until the feedback
>> >occurs, and turn down the appropriate frequency slider on the graphic
>> >the feedback disappears. And repeat until the desired volume level is
>> This is really not the way to do it. You'll only make it worse because
>> it will get more difficult to hear what is said through the PA.
>> There is another way though developed by someone named Larssen. He
>> came up with a system that shifts all frequencies by a few Hertz.
>> Reply to nico@nctdevpuntnl (punt=.)
>> Bedrijven en winkels vinden? Adresboekje.nl
>This is not true. The method described with the graphic equalizer works
>very well in practice (large sound systems). We used 27 band equalizers in
>my experience. When you cup the mike, it howls (positive feedback) at 2 or
>3 spots in the spectrum, which you turn down 3 to 6 dB until the howl stops.
>Once this is done, the system usually will not feed back at all, even if you
>stand out in front of the speakers. Further, the clarity of sound is
>extraordinarily good. But this is mostly due to the use of the equalizer in
>the first place along with pink noise leveling done in the actual room where
>the system operates.
I used to work for a company which installed a lot of PA systems in
churches. We either used frequency shifting or a Behringer 'feedback
destroyer'. One of the problem with feedback is that it highly depends
on how many people are in the church. The Behringer units sometimes
where out of 'bands' to suppress enough. A graphic equalizer doesn't
have enough precision. Besides, in many cases wireless microphones are
being used. You need an adaptive system to get rid of feedback and we
always tested the system with RASTI. Using an equalizer can have a
negative effect on the test. The sound may be clear, but the spoken
word can still be difficult to understand.
Another method we used to raise the feedback threshold was to allow
only one open microphone at any given time (priority) or close unused
microphones (level detection).
Reply to nico@nctdevpuntnl (punt=.)
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