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[DPRG] Feedback prevention

Subject: [DPRG] Feedback prevention
From: Ed Paradis legomaniac at gmail.com
Date: Mon Oct 18 09:39:24 CDT 2004

Notched analog filters actually work pretty well, if you make them
adujustable.  From my expereince, in any given situation, the feedback
frequency is pretty well known, if only for that one situation.

dial in you notch, and you're good to go.

Adding delay will lower the frequency, but reduce the 'listenability'
for those close to person with the mic who can still hear the speaker.

Honestly, a simple PA circuit with some filters slapped on the end is
fairly trivial if you're not looking for a ton of power, so it just
depends on what is more valuable: time or money.

If buying something is just the only way to go, look at the Radio
Shack PAs, but used.  They're not too bad, and second hand the price
is reasonable.

Heck, if you really wanted to c heap out, get one of these kareoke
machines, and trick it to never play music.  Those things go for
loss-leader prices occasionally, so we're talking REAL cheap.

Ed

On Mon, 18 Oct 2004 09:11:20 -0500, Kipton Moravec <kip at kdream.com> wrote:
> I searched and did not find anything useful yet. Still looking
> 
> I did find a discussion from a company that makes such things.
> http://www.sabine.com/RESOURCES/FBX/Literature/FBX-Best-Lit-LRZ-030120.pdf
> 
> It looks like they use notched filters at the point of the feedback
> frequency.  But that frequency is dependent on a bunch of things like mike,
> amp, speaker, room, position -- basically everything that can very from one
> time to the next, or as the person with the microphone moves.
> 
> Does not seem trivial.
> 
> Kip
> 
> 
> 
> At 07:03 AM 10/18/04, you wrote:
> >I tried a google search on "microphone feedback prevention schematic" and it
> >returned around 8760 hits for me.
> >There has to be a circuit design you could use out of all of that someplace.
> >It had a lot of techniques on reducing feedback problems too.
> >
> >-----Original Message-----
> >From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On Behalf
> >Of Dale Wheat
> >Sent: Sunday, October 17, 2004 10:49 PM
> >To: dprglist at dprg.org
> >Subject: [DPRG] Feedback prevention
> >
> >Pres. John has tasked me with investigating possibilities for a
> >club-owned PA system for our public events that need public addressing.
> >
> >One of the criteria was automatic feedback elimination.  This is a
> >pricey add-on to any system, it turns out.  An outboard unit will cost
> >between $300 and $500.  It is also available as a feature of powered
> >mixers in the $600-$900 range.
> >
> >To me this seems like a lot of $$$ for something that surely someone
> >amongst us can whip together with a DSP, duct tape & bailing wire.
> >
> >Any suggestions?  I'd be willing to do most of the
> >building/coding/whatever if someone can point me in the right direction.
> >   I have extensive microcontroller experience, but have only glanced at
> >DSP stuff, and that a long time ago.
> >
> >Wouldn't a short delay (20-50ms) cancel out most feedback?
> >
> >Thanks,
> >
> >Dale Wheat
> >http://dalewheat.com
> >(972) 486-1317
> >_______________________________________________
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> >
> >
> >
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