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Preventing Audio Feedback
in Live Sound Systems

It is best to do what is in your control to minimize feedback in the first place.

1) Use a Directional Microphone - Virtually every mic in live sound is a cardioid, which is more sensitive to sound hitting it straight on, but if you're walking into an unknown situation some knucklehead might have an omni. People purely involve in recording or video production might not even know what a cardioid mic is, because they can never cause feedback and might very well have omnis.

2) Use a MORE directional Microphone - Beyond cardioid there is Supercardioid/hypercardioid (same thing), which have an even tighter pattern. Beware though that whereas the point of maximum rejection for a cardioid is directly behind the mic, a hypercardioid's dead points are off to the side more. For both it's good to look at the polar pattern of the mic involved. A lot of cardioid mics get rather omni at low frequencies, and all these directional mics have modest side pickup. They aren't as directional as we would like.

3) Teach Good Microphone Technique - While we can't give the whole audio 101 course to a client, we can suggest good handheld mic habits like a) talking straight into a mic, not off axis, and not at the ceiling b) holding the mic close to your mouth, not by your navel, and of course c) don't point the microphone at the speakers. One more thing, do not cup the back of the mic like you see rappers do. That effectively turns it into an omni because you're blocking the vents that help make it directional.

4) Keep the speakers as far away as possible and pointed away - If the speaker sound getting into the mics is the problem, then point them away!

5) If you've got acess to a graphic equalizer, then "ring the room" out by gently turning up the system when no one is there, and turning down the frequencies that start to ring. By doing so you don't amplify the frequencies that the room reinforces naturally (by the walls vibrating), and the result is a flat frequency response that will sound natural.

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