| 摘要 |
PURPOSE:To prevent the howling in response to the fluctuation of delay time of an acoustic path, by measuring the delay time of sound waves between a speaker and a microphone, generating a pseudo audio signal based on the measurement and subtracting the signal from an input signal to the microphone. CONSTITUTION:A reception signal 22 inputted to a reception system input terminal 21 is branched partly and applied to a variable delay line 212 and given to a pseudo sound path 213 with a delay. This output is given to a subtractor 210, where a pseudo sound signal is subtracted from the signal inputted from a transmission system input terminal 28. The delay time at a variable delay line 212 is controlled with an output of a delay time measuring device 215. The measurement of the delay time is realized by providing an ultrasonic wave generator near a speaker 24, locating an ultrasonic wave receiver near a transmitter 27 and measuring the propagation time. Thus, since echo can be cancelled while correcting the delay time one after another, the howling can be prevented effectively. |
