Patent ID: 7787641

Claim:
A sound reproducing system, comprising a main control unit, and at least one secondary control unit, wherein: the main control unit includes an adapter, a voice source input interface connected to at least one voice source, at least one automatic level control circuit connected to the voice source input interface and corresponding to the voice source, at least one first power amplification circuit connected to the automatic level control circuit, and at least one first transmission interface connected to the first power amplification circuit; the secondary control unit includes a second transmission interface connected to the respective first transmission interface of the main control unit, a volume control circuit connected to the second transmission interface, a second power amplification circuit connected to the volume control circuit, an output interface connected to the second power amplification circuit and connected to at least one external loudspeaker, a microprocessor connected to the volume control circuit, an operation device connected to the microprocessor, and an indication device connected to the microprocessor; the operation device is operated to control the microprocessor which controls the volume control circuit to output a voice signal from the voice source with a determined volume, the indication device indicates the voice signal, the respective automatic level control circuit of the main control unit maintains the voice signal output at a constant level, the respective first power amplification circuit of the main control unit converts the voice signal into a larger voice signal, the respective first transmission interface of the main control unit outputs the larger voice signal which is transmitted into the second transmission interface of the respective secondary control unit, the volume control circuit of the respective secondary control unit converts the larger voice signal into a smaller voice signal, and the second power amplification circuit of the respective secondary control unit converts the smaller voice signal into a larger voice signal which is transmitted through the output interface of the respective secondary control unit into the external loudspeaker so that the external loudspeaker emits the voice outward.