Few things are more annoying than that ear piercing squeal that occurs when someone passes a microphone too close to a speaker. You usually try to avoid this by positioning your speakers away from the area where the mics will be used. Unfortunately, this is not always possible. You can also try eliminating the frequencies that are causing the feedback but that means you are going to degrade the audio to some degree.
The solution is to incorporate an electronic feedback eliminator into your sound system. This device will detect feedback frequencies within a fraction of a second and stop them instantly and unnoticeably. Instead of eliminating frequencies altogether you will only eliminate them when feedback occurs. Below is one feedback eliminator that is widely used by professional KJs.
Behringer FBQ2496 Feedback Destroyer Pro
Within fractions of a second, the Feedback Destroyer Pro's ingenious search algorithm locates feedback frequencies and sets extremely narrow, 1/60-octave filters, leaving the desired signal virtually untouched. The result: a rich, full sound without feedback. And without headaches.