| 摘要 |
PROBLEM TO BE SOLVED: To obtain large output sound pressure even when the vibration amplitude of a diaphragm is small. SOLUTION: A sound signal to be reproduced is input from an input terminal 10. A high frequency signal with fixed amplitude is output at a fixed frequency from a high frequency signal source 12. The frequency of the high frequency signal is higher than an audible frequency and is set to 10 to 1,000 times e.g. as much as the upper limit frequency of the sound signal to be reproduced. An amplitude modulation circuit 14 modulates the amplitude of the high frequency signal by the sound signal. The amplitude-modulated high frequency signal has a waveform to be deflected only in the same polarity direction according to the polarity of a sound signal waveform. The amplitude-modulated high frequency signal is amplified by an amplifier 16 to drive a speaker 18. The speaker 18 is a speaker of a type that the displacement amount of the diaphragm follows an application voltage and is composed of an electrostatic speaker, a piezoelectric speaker, or the like. COPYRIGHT: (C)2009,JPO&INPIT
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