| 摘要 |
PURPOSE:To prevent sound reproduction from the influence of detection by a microphone by feeding back the output of the microphone to the input side of a speaker at a frequency range lower than the frequency setting up the distance between the speaker and microphone to 1/4 wavelength. CONSTITUTION:An adaptor 25 is arranged close to a speaker box 15, and the microphone 11 and a feedback circuit are incorporated in the adaptor 25. If a feedback variable is set up to 0dB or less at the frequency range lower than the frequency setting up the distance between the speaker and microphone to 1/4 wavelength, i.e. at the frequenct setting up the phase difference between the reproduced sound of the speaker 13 and the detected signal of the microphone 11 to 90 deg. or more, the sound receiving pressure of the microphone 11 is reduced and the feedback variable is automatically reduced, so that trouble such as oscillation is not generated. |
