US Patent 7787641 Sound reproducing system for use with multiple rooms

A sound reproducing system for use with multiple rooms includes a main control unit, and at least one secondary control unit. Thus, the respective automatic level control circuit maintains the voice signal output at a constant level, the respective power amplification circuit of the main control unit converts the voice signal into a larger voice signal, the volume control circuit of the respective secondary control unit converts the larger voice signal and the noise produced during transmission into a smaller voice signal, and the power amplification circuit of the respective secondary control unit converts the smaller voice signal into a larger voice signal output, thereby producing a voice signal output with a higher quality.