Audio feedback on microphone from loudspeaker on IP system

[jp123 0]

Hi

I was hoping someone may be able to help with an audio feedback problem on a CCTV system I have.

 

There is a Hikvision camera (DS-2CD2655FWD-IZS) which has a microphone connected to an audio input. The camera then has a horn speaker connected to an audio output. The camera is then wired back to a Hikvision NVR.

 

The sound from the Mic works fine when the speaker isn't being used. As soon as the push to talk function on the IVMS-4200 app is used a lot of feedback happens through the Mic. The app doesn't have an audio cutoff for the microphone built into it when you use the talkback functions.

 

I have used functions in the camera for echo noise cancellation and tried adjusting microphone levels in the camera.

 

Currently, the speaker is about 5 meters away from the mic and have been trying to come up with a way to reduce the feedback on the microphone without massive loss of quality.

 

Ideally, the speaker isn't wanting to be moved so if anyone has any thoughts on how I can get around this.

[jeromephone 6]

the speaker will act as a microphone if it is pointed at the microphone. If you move the speaker or the mic it should eliminate the problem for instance have you ever been in a meeting room with overhead speakers and someone is speaking into a mic and you get that squeal. If the mic is moved a few feet away the feed back goes away as the speaker is too far away to act as a microphone.

[the toss 0]

Audio feedback is caused by an acoustic loop. Sound into mic ---> amplification ---> sound out of speaker ---> higher level sound back into mic ---> amplification ---? higher level sound out of speaker and so on. There are a number of ways to address the problem. The volume can be set to below the feedback threshold which in itself will depend on a number of factors. The physical orientation relashionship of the speaker and microphone can be changed to decrease the level of signal received from the speaker. The immediate environment can be changed to reduce (or dampen) the audio reflection from the speaker. In large sound reinforcement systems it is common to use a feedback eliminator between the mixer/preamp and the power amp. This inserts either a small time delay or a phase delay in the signal to break the resonance loop between input and output in high gain amplification.