A sound control method includes following steps. Firstly, a controller commands a first ultrasonic transmitter to emit a first ultrasonic wave. Then, in a first time interval, the controller records a first received signal waveform received by an ultrasonic receiver. Then, the controller commands a second ultrasonic transmitter to emit a second ultrasonic wave. Then, in a second time interval, the controller records a second received signal waveform received by the ultrasonic receiver. Then, a playing mode of at least one speaker is controlled according to the first received signal waveform and the second received signal waveform.