Need Help Making a 3 pole active Low-Pass Filter

Pro Audio Asylum

Pro studio recording equipment and music production/industry.

Hello All,

I'm new to this forum, and am in search of a 3 pole active Low-Pass filter, apparently.

I am a videographer using Sony ECM 44b and 55B microphones and a Shure M367 mixer. I occasionally have to set up in conference rooms that are equipped with ultra-sonic motion detectors (used to turn out the lights when no one is there.) The signal emitted by these detectors (at 25 kHz) is picked up by my microphones and creating havoc with my recording. First; it looks like a very loud scream on the VU meter, and trips the limiter, muting the audio quality. It also is converted into a high-pitched whine by one of my recording decks. The main problem, though, is the VU meter/limiter.

I need to eliminate the signal between the microphone and the mixer. I tried a commercially available passive filter, but even two of them in line did not reduce the signal enough. The manufacturer suggested I need a 3 pole active low-pass filter, which they do not make.

I am willing to build such a filter myself, and I even have found some designs or plans that might do the trick - but I can't understand them at all. They are always written way above my level, and use diagrams written in code that I can't decipher.

So; I need help understanding and picking a design, or creating one, and reducing said design to diagrams and instructions I can understand and build.

Can anybody here help me with my project? Or point me to some information I can understand?

Any help would be much appreciated.

-Hjourzt

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Parts Connexion

Topic - Need Help Making a 3 pole active Low-Pass Filter - Hjourzt 18:53:16 09/29/12 (3)

RE: Need Help Making a 3 pole active Low-Pass Filter - bassbinotoko 15:22:50 10/27/12 (0)

RE: Need Help Making a 3 pole active Low-Pass Filter - Palmer 10:34:30 10/14/12 (0)

RE: Need Help Making a 3 pole active Low-Pass Filter - Palmer 11:31:33 10/03/12 (0)

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