Have any one try to eliminate the feedback picking up from microphones.
Or is there a way to cancel out the feedback picked up from the nearby speakers ?

 

Are the speakers pointed towards the microphone?

 

The problem almost always is caused by speaker to mic feedback. The quickest and cheapest way to eliminate the feedback is to break the loop by moving either part. If you can't move the mic or speaker you can buy a system that senses feedback and electronically eliminates it. I worked on such a system with a fast processor, but I don't remember their name. That was a while back so you are better off searching the web.

 

The problem is that due to the environment I am getting feedback at some mic locations.
It's not the high pitch oscillation but rather the low frequency oscillations. Like the one you get when you enclosed the the mic in your palm the oscillation slowly builds up to the point that amp cuts off. I can stop it by reducing gain but that reduces the volume too.
No matter where the speaker is it happens due to the objects with in the room which cannot be moved.
I am looking for a way to actively cancel out that feedback.

 

If it lower than 400 Hz then just use a high pass and cut the bass response. Is the mic just for human speech?

 

The problem is that due to the environment I am getting feedback at some mic locations.
It's not the high pitch oscillation but rather the low frequency oscillations. Like the one you get when you enclosed the the mic in your palm the oscillation slowly builds up to the point that amp cuts off. I can stop it by reducing gain but that reduces the volume too.
No matter where the speaker is it happens due to the objects with in the room which cannot be moved.
I am looking for a way to actively cancel out that feedback.

put a second microphone at 90-degrees to the first to capture environmental noise and use common mode (differential amplifier) to amplify only the directional noise from the primary microphone. It takes some time/effort to balance the two signals if you have reflections and not in an open space but, it can work. Essentially a noise-cancelling microphone.

 

The mic for just human speech.
Two mics at 90 deg to a differential amp might just work.

Or how about a band pass filter ?
Just the speech area ?

 

The type of microphone is important too.
Unidirectional mics give best results in this situation.

 

There are whole books about sound system engineering. In one case, I increased the gain of a church's sound system by 20db with a 30 band graphic equalizer. Similar to Gopher's idea, 2 identical mics aimed the same way but wired 180 degrees out of phase eliminates all, "far field" sounds and only picks up sound within a few feet of the mic pair. Trying to do active gain control or adding a significant time lag is expensive, therefore those options come AFTER paying attention to the basics like "number of open mics", reflections, directionality of the speakers and mics, etc.

oh yeah, limiting bandwidth to only the human voice range.

 

The Behringer Shark is quite effective at eliminating feedback. However it does so by eliminating (filtering) the offending frequencies so a little of the sound quality can be lost.Not so important for the spoken word but not ideal for some musical instruments or singers.

 

http://shure.custhelp.com/app/answers/detail/a_id/2844

Put a 6.8 uf cap, or maybe 10 uf, in series and see what you get. A 6db roll off starting around 250-300 Hz is what you need. Might even go as high as 500 if you need more suppression.

 

The Behringer Shark is quite effective at eliminating feedback. However it does so by eliminating (filtering) the offending frequencies so a little of the sound quality can be lost.Not so important for the spoken word but not ideal for some musical instruments or singers.

Interesting.