What is feedback

Feedback occurs when a microphone (or other input like a guitar pickup) detects enough sound from a speaker that when the signal is run through the system it becomes louder than the first time and the mic picks up an even louder signal.

Note that feedback requires an acoustic input such as a mic (or guitar). A CD player will never be the source of feedback.

Solving Feedback

• Mic is too close to the speaker
• Mic is too far away from the source
• Mic gain is too high (usually because the source is too far away)
• Mic is pointed at the speaker or sound is being bounced into the mic by a cupped hand over it or a reflecting surface like a wall.

Distance
If you double the distance from the speaker to the mic, you just cut the sound by 4.

If you halve the distance from the mic to the source you just improved the gain before feedback by 4.

Direction
Most microphones and speakers are directional. The microphone picks up the most in the direction it is pointed and picks up the least in the direction it is pointed away from. Make sure the mic is behind the speaker and/or pointing away from it.

Note: Some microphones (and some speakers) are omni directional - these pick up just as well from the back as from the front.

EQ
It is possible to use a graphic equalizer or parametric EQ to notch out the problem frequencies for a particular mic location. Basically you put an EQ cut at the frequency or frequencies where the mic is feeding back.

Note: Applying EQ to reduce mic feedback should be the last resort. EQ changes should be minimized to avoid reduction in sound quality.

Feedback Eliminators
Automatic feedback elimination can be done using Digital Signal Processors.

Unfortunately Feedback Eliminators are expensive and still won't solve all the problems. It is best to use conventional methods first.