Microphone "whistel" canceler schematic need!

[geminni]

I'm not shure if that is the corect name for the thing i would like to make.
Is there something that can protect speakers and amlifier from those nasty whistles when microphone gets near loudspeaker?

[Dag]

This is not possible. (Hm..just because I say so someone will have a solution....but that's ok I guess) The whistel sound is caused by the delay in the microphone-electronics-speaker-microphone loop. If you filter the whistel out you will also filter out the audiosignal.

[megajocke]

http://www.behringer.com/DSP1124P/index.cfm?lang=ENG

It uses some kind of search algorithm that controls a parametric equalizer

[pinkmouse]

These work pretty well. Behringer do one too, but I have never used theirs. For diy, the only thing you can do easily is a high Q swept parametric.

[phase_accurate]

The oldest versions of feedback-killers (or feedback eliminators) used frequency shifters that shifted the whole audio spectrum up or down. The frequency-shift was between some tenths of a Hz up to ca 20 Hz.
The working principle was similar to the so called phase method for SSB.

Regards

Charles

[geminni]

Originally posted by pinkmouse
These work pretty well. Behringer do one too, but I have never used theirs. For diy, the only thing you can do easily is a high Q swept parametric.

I had the idea about that high Q. Couple years ago me and my friend were doing some experiment with mic and 3-way speaker. Each speaker had its "own" wistle frequency. I will have to do same test now to determine if this is true. Back then we were just beginers and did not pay atention on details. If the test shows that there is one frequency for each driver, in my case for 2-way PA speaker, then i would hace to build 2 Q filters that will choke those 2 frequencies.
Maybe i'm to paranoic about these stuff and i'm asking too much for total amplifier protection

[pinkmouse]

Make the EQ swept. Feedback changes with speaker positioning and the room.

[geminni]

Forgot to add that i think mic is allso a blame for the frequency. Maybe diferent mic will give diferent frequency so there will be need for the variable frequency

[pinkmouse]

Indeed.

[imix500]

Correct system eq and speaker placement will help a lot here. Also, you can try backing the system up to the mics with system delay- this will help a bit too. The "feedback eliminators" work ok, but they can be too aggressive and filter out audio that is not feedback.