| 摘要 |
<p>PURPOSE:To prevent howling by arranging pressure sensing elements in contact with diaphragms of microphones and then by lowering gains of amplifiers when outputs of pressure sending elements are small. CONSTITUTION:A sound emitted toward microphone 4 vibrates diaphragm 5 and audio converting elements 6 converts its vibrations into an electric signal, which is amplified and supplied to speaker 12 to emit a reinforced sound. On the other hand, the sound pressure of the emitted sound inflects diaphragm 5 and an output voltage developed across pressure sensing element 7 corresponding to the inflection is amplified and polarity-inverted by inversion amplifier 13 into control voltage VC, which controls the gain of gain control part 9. Then when the output voltage of pressure sensing element 7 is low, control voltage VC increases and the gain of gain control part 9 decreases. Consequently, when there is no user in front of microphone 4, the gain of the amplifier lowers, so that its howling can be prevented.</p> |
