| 摘要 |
<p>PURPOSE:To generate a high sound pressure from a small sized piezoelectric sounder by selecting a resonance frequency of a package case to be nearly 2f0, where f0 is a resonance frequency of a piezoelectric sounder driven by a drive signal boosted by a boosting coil. CONSTITUTION:A piezoelectric sounder 1 is connected between a power terminal 3 and a collector of a transistor(TR) forming an output terminal of a drive circuit of the piezoelectric sounder 1 together with a boosting coil 4. With a rectangular wave whose frequency is f1 fed to an input terminal 5 from an oscillation circuit 6, a TR 2 is turned on, off and a voltage of a battery 7 applied to the coil 4 and the sounder 1 is turned on, off. In this case, when a rectangular wave whose frequency is f1 is applied to the terminal 5, it is the same as the state that a sinusoidal wave whose frequency is 2f1 is applied to the terminal by the action of the coil 4 in the sounder 1. Since the resonance frequency of the cavity is set to be 2f1, the sound pressure at the frequency of 2f1 is increased, resulting that the sound pressure at the frequency f1 is increased.</p> |
