| 摘要 |
PURPOSE:To obtain an easy-to-hear sound even if the level of an external noise increases by controlling an amplifier depending nearly upon the external noise by canceling howling between a loud speaker and microphone. CONSTITUTION:Signal source 1 drives loud speaker 3 via variable amplifier 2. Microphone 4 is coupled with loud speaker 3 a loosely as possible by fixing its position and direction and sound insulating board 20 is provided at need. An input to microphone 4 is amplified by microphone amplifier 5 and then supplied to rectifying processor 6, which generates a control signal to control the gain of amplifier 2, so that when the output of the microphone increases in level due to an external noise, the output of amplifier 2 will be increased generally. However, a positive feedback state where the gain of amplifier 2 is held increased may occur when the increased volume of speaker 3 causes microphone 4 to generate its output and in this case, non-linear control, etc., which does not increase the gain of amplifier 2 above a certain value is recommended. |
