| 摘要 |
PURPOSE:To generate a low sound from a subminiature speaker and to improve the frequency characteristics, by designing the resonance frequency of the speaker higher than the audible frequency, taking the resonance frequency as a center, and driving the speaker with a signal modulated with the acoustic signal. CONSTITUTION:A piezoelectric oscillator 305 of a piezoelectric speaker used for an electronic wrist watch is stored in a watch storing section 303 constituted with a watch case 301, a cover glass 302 and a back cover 304, the oscillator 305 is sticked to the back cover 304, and the resonance frequency is designed higher than the audible frequency with the thickness of the oscillator 305 and the back cover 304. The amplitude modulation circuit driving the oscillator 305 is provided with a transformer 506 inputting a signal from a carrier input terminal 501, a transistor TR505 and a transformer 508 inputting the sound from the acoustic signal input terminal 503. The signal is modulated with the acoustic signal by taking the resonance frequency as a center, a low sound is generated from a subminiature speaker and the generation of the sound pressure over each frequency is made effective. |
