MOTTAGARDON FOR LJUDVAGOR BESTAENDE AV EN RESONANSSKIVA OCH EN FOR DENNAS AV LJUDVAGORNA FRAMKALLADE SVENGNINGAR REAGERANDE PIEZOELEKTRISK MIKROFON AV KRISTALLTYP

摘要

A sound-wave receiving applicance comprises a resonance panel and a crystal type piezoelectric microphone responsive to oscillations generated by the soundwaves, said microphone being adapted for connection to an amplifier. The crystal of the microphone is subjected, between two pole members, to a mechanical initial pressure to increase the pressure sensitivity of the microphone relative to the resonance panel. The receiving applicance preferably has means for manual adjustment of the initial pressure which is absorbed by the resonance panel via one pole member. The resonance panel of the receiving appliance preferably is made of a material, such as a cellular plastic, having a higher porosity and a lower specific gravity than ordinary wood.