Feedback is a common problem experienced in live sound setups. It occurs when the sound entering the microphone is amplified, sent through a speaker, picked up by the microphone, re-amplified and sent through the speaker again, over and over. The result is the familiar ringing tone we have all come to despise.

Common causes of feedback include pointing the microphone directly at a speaker, placing the microphone too close to speakers or too far from the sound source, or turning the mirophone up too loud. There are some other factors that contribute to feedback, such as poor room acoustics (lots of echo) or having too many open microphones.

The simplest and most effective way to reduce/eliminate feedback is through proper microphone placement. Ideally, microphones should be placed behind the speakers and facing in the opposite direction. They should also be placed as far from the speakers and as close to the sound source as possible. Reducing the number of open microphones and using directional microphones will also help.

In some situations, these techniques may not be possible or practical, such as rehearsing in a rather small room or garage. In such cases, treatment of hard surfaces (glass, wood, etc.) with acoustic foam can be helpful.

If these techniques do not solve the problem, you may need to use an equalizer or feedback destroyer. An equalizer will allow you to manually reduce the volume of the specific frequencies that are feeding back (a technique known as "Ringing Out" a sound system). A feedback destroyer will detect frequencies that are feeding back and automatically reduce those frequencies.