2. If you speak one word at the microphone at a level of 80 dB and the loudspeaker returns that word to the microphone at 80 dB, then you can go home. The sound system will repeat the sound all day, "chasing its tail" from microphone to loudspeaker.

3. When a sound signal to microphone is amplified and used to drove a lauds peaked, some of the amplified sound returns to the microphone and is amplified again. this is called feedback Amplified sound to listener 80 db source input to microphone 80 db feedback to microphone Signal from microphone amplified to speakers.

4. The situation depicted here is the theoretical maximum gain where the feedback signal is equal to the input signal. It is not practical to get this kind of gain, so you seek to stay considerably below this - at least 3dB is a common rule. Any time the feedback signal is comparable to the input signal, it represents a distortion or degradation of the signal. The amplified signal is coming back to the microphone with a delay and with whatever "coloring" the sound system and the room give to it.

5. Ringing the System" When the gain on a sound amplification system is turned too high, the output from the loudspeaker changes to an unpleasant, loud, usually high-pitched sound. This is the result of too much feedback, but instead of reproducing the sound being amplified, it usually produces a single pitch at the frequency which is amplified the most by the sound system/room combination.

6. source Loudspeaker listener Microphone

7. Note that an ideal sound system responds equally to all frequencies. This not only gives a high fidelity reproduction of the sound, it also gives a higher potential acoustic gain from the amplifier system. The horizontal dashed line which represents the ideal system on the right above is still well short of the feedback level when the other system begins to ring. The procedure for filtering the frequency response to approach the ideal flat response is called equalization

8. When the gain on a sound amplification system is turned too high, the output from the loudspeaker changes to an unpleasant, loud, usually high-pitched sound. This is the result of too much feedback, but instead of reproducing the sound being amplified, it usually produces a single pitch at the frequency which is amplified the most by the sound system/room combination