The back -listening system is a sound system specially established to solve the problem of actors and bands on the stage. During the performance, the actor and the band are behind the main vocal speaker. If they cannot hear their own vocal effects, they cannot find the feeling of the performance. Therefore, for the audio system of theater and the song and dance hall, in addition to the audio system of the main sound field, the hearing system is also essential. In addition, when the audio system fails, the return system can also be used as an emergency audio system to avoid the cold field situation. On general occasions, 20%of the power field power return system power is used. For example, the main vocal field power is 2000W, so the power return system should be selected by 400W. In the listening system, in order to make the sound return loudness and good effect, the power of the return amplifier should be greater than about 1.3 times the power of the return speaker. In actual use, the output power of the amplifier will be adjusted on the spot. If the power return system is too small, it will make the return system lose meaning; the power return system is too much, and it will produce the adverse effects of vocal feedback. Therefore, special attention should be paid to the adjustment of the volume and effect of the system.