Abstract: An electromagnet is formed of a combination of an iron support, an iron piece, and a solenoid, and an interrupter is provided to intermittently excite said electromagnet. A cylindrical diaphragm, equipped with an armature so disposed as to come against said iron piece, covers said iron support so that said iron piece, said solenoid, and said interrupter may be enclose therein.

Abstract: A multifrequency piezoelectric sound-generating system is provided with a piezoelectric vibrator for generating audible sound at two or more resonance frequencies, an oscillator circuit connected to the piezoelectric vibrator for oscillating at one of the resonance frequencies, and a modulator circuit connected to the oscillator circuit for amplitude-modulating the oscillator circuit with a modulating frequency substantially equal or close to a frequency separation between the resonance frequencies to energize the piezoelectric vibrator with frequency-modulated waves to generate multifrequency audible sound.The modulator circuit may have a frequency divider that is operative in response to an oscillating frequency in the oscillator circuit for dividing or counting down the oscillating frequency into the modulating frequency to modulate the oscillator circuit therewith.