Light and sound whistle should pay attention to the following points: power amplifier: self amplifier will produce very big power output, and beyond with the ability of PA equipment, will not only have a whistle, sometimes even burn the power amplifier and sound equipment.

Comb filtering effect: in the feedback coefficient is close to 1, often will have a comb filtering effect, delay superposition between field and direct sound, also can make the sound field than the original sound field in the pitch becomes narrow and squeak.

Information: microphone microphone (Microphone) commonly known as the microphone, the sound signal received a direct sound coming from the speakers, reproduction and interior, exterior wall or other objects reflected sound 3, 2 are easy to form a sound feedback.

Delayed feedback: the sound field of the loudspeaker is delayed feedback, so that the whole system forms a series of delayed echoes, and the comb filter effect is increased, and the reverberation of the reverberation and the obvious distortion is generated.

    in sound practice, lighting and sound engineers summed up a lot of feedback suppression method of sound system, acoustic experts take some effective measures to eliminate acoustic feedback, electro acoustic experts developed a variety of electronic devices, in order to reduce the occurrence of acoustic feedback phenomenon, the feasible measure after, and achieved good results.