| 摘要 |
PROBLEM TO BE SOLVED: To provide an alarm for producing a sufficient acoustic output regardless of difference in resonance frequency due to manufacturing tolerance or the like without increasing costs and enlarging its size. SOLUTION: An alarm 1 includes a resonance chamber 51 resonating in a sound wave of a predetermined resonance frequency; a piezoelectric vibration plate 50 being installed in the chamber 51 and outputting a sound wave of an arbitrary frequency; and an acoustic control unit 60 varying the frequency of the sound wave to be outputted from the plate 50. The control unit 60 varies the frequency of the sound wave to be outputted from the plate 50 in a first frequency zone 101 including the resonance frequency. COPYRIGHT: (C)2009,JPO&INPIT
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