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 Forum index » How-tos » Production - engineering/mixing
Stopping feedback in small spaces with live mics
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nobody



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PostPosted: Wed Feb 24, 2010 2:28 pm    Post subject: Stopping feedback in small spaces with live mics
Subject description: Can it be done?
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Is there any way to prevent feedback with a mic in a small space that has a direct line of sight to the loudspeakers? I want to use my mic (the only one I have, can't afford to buy another right now) during Spring Equinox to do some live vocoding. Unfortunately, I will be turning things up a bit, and a test just now gave off lots of feedback (thankfully I have a switch in the mic cable, so I can cut it off in half a second).

I'm not expecting there to be a way to prevent feedback from happening, but since I don't know everything, I thought I'd ask anyway.

And oh - the speakers can't be moved. Well, they can, but I would really rather not move anything large. Even if I point them away from the mic, in a small space that wouldn't matter as the sound would end up in the mic anyway.

Worst case is I record the vocoding beforehand and it simply won't be one of the live parts.
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seraph
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PostPosted: Wed Feb 24, 2010 2:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

what about using headphones instead of loudspeakers?
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nobody



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PostPosted: Wed Feb 24, 2010 3:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

I want to be free to move around. Plus, I wear hearing aids, and it's a pain in the ass - let alone the ear - to keep a small pair of phones balanced over the mics of the aids. I put up with it when laying vocals, but a live show - even a radio show from my studio - would be uncomfortable and clumsy.

I have a device that let's me wirelessly input sound directly into the aids, but the power adapter died years ago and I haven't gotten around to replacing it. Getting one with the correct voltage, even a generic one from Radio Shack, is still more than I want to spend right now for something I would only use intermittently (and that might not even be why it's not working). It would be cool to see what I could do with it, though. I'll definitely need it - or a replacement for it - during a live, in-person show.

Otherwise, I'd use phones. Cool
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modulator_esp
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PostPosted: Wed Feb 24, 2010 5:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

the only way I can think of to limit feedback if you can't use headphones is to
1. position the mic so it is picking up as little sound as possible, e.g. point away from speakers, or put behind speakers
2. reduce any reflected sound as much as possible using some form of damping materials
3. eq out any resonant frequencies with a graphic eq

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RF



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PostPosted: Thu Feb 25, 2010 2:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

4. Keep the mic gain as low as possible and 'eat' the mic.

bruce

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nobody



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PostPosted: Fri Feb 26, 2010 6:42 am    Post subject: Reply with quote  Mark this post and the followings unread

I might try eating the *glorb grind scrinch argh* the mic. Razz
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PostPosted: Fri Feb 26, 2010 9:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Well I don't know if this would work, but you could try making a cardboard or plastic cone around the mic to block out sound from the opposite direction. Just a guess.

Les

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BananaPlug



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PostPosted: Fri Feb 26, 2010 9:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Here are a couple throw-technology-at-it solutions I've heard of. The first is an old idea which never really caught on. I think there are commercial products based on the second. Might be fun to experiment.

Tape a second mic to your mic, pointing the opposite direction. Then flip the phase on that mic and mix in enough of it to cancel the PA system.

Patch a frequency shifter between your mixer and the PA with as small a shift as it can manage. The idea is that the shift is not noticeable but feedback can't build because it slides away from the resonant frequency.
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nobody



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PostPosted: Fri Feb 26, 2010 11:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Les, the cone would have to be sticking out of the back of my head, because the speakers are right behind me. It would be a variation of this: http://www.geeksugar.com/Totally-Geeky-Completely-Crazy-Privacy-Scarf-190643

That image never fails to crack me up.

Banana, I like the freq shifter idea. I only wish I could afford to go and get one (a hardware unit) to try it. I think it would be useful for other things, too!
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BananaPlug



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PostPosted: Sat Feb 27, 2010 6:13 am    Post subject: Reply with quote  Mark this post and the followings unread

audiodef wrote:
Banana, I like the freq shifter idea. I only wish I could afford to go and get one (a hardware unit) to try it. I think it would be useful for other things, too!


Get one of these and do it in stereo!
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EdisonRex
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PostPosted: Mon Mar 01, 2010 8:35 am    Post subject: Reply with quote  Mark this post and the followings unread

http://www.studiospares.com/Mic-Accessories/SE-Electronics-Instrument-Reflexion-Filter/invt/422160
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telstarmagikistferrari



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PostPosted: Fri May 28, 2010 4:48 am    Post subject: Reply with quote  Mark this post and the followings unread

ER that's exactly what I pictured when I read the title of this thread.
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