| 摘要 |
PURPOSE: To provide a simplified device by which the distance between a loudspeaker and a microphone is measured by means of ultrasonic waves. CONSTITUTION: A sing-along apparatus is composed of a music player 4, an audio amplifier 6, loudspeakers 8, 9, 10 and a microphone 11. A time-sharing ultrasonic pulse signal which is generated by an ultrasonic oscillator 1, an ultrasonic-generation-timing creation circuit 2 and an analog switch 3 is superposed on the output of the audio amplifier 6 via a mixer 7, and a superposed signal is transmitted sequentially to the respective loudspeakers 8, 9, 10. Sounds by the respective loudspeakers 8, 9, 10 are received by the microphone 11, a received signal is passed through a high-pass filter 12, and an inaudible-band ultrasonic signal is taken out so as to be output to a distance-between- loudspeaker-and-microphone measuring circuit 14. A pulse signal by the ultrasonic-generation-timing creation circuit is input simultaneously to the circuit 14, their timings are compared, the ultrasonic arrival time between the respective loudspeakers 8, 9, 10 and the microphone 11 is found, and the distance between them is measured on the basis of the spatial propagation speed of ultrasonic waves. |
