PURPOSE: To heighten a mechanical impedance of a case and to prevent the vibration interference for acoustic characteristics which are held by a diaphragm by installing a dome-shaped front air chamber board part and a cylinder-shaped rise part having the plural sound releasing holes solidly with the case.
CONSTITUTION: A ceramic piezo-electric body 17 is stuck to a metallic diaphragm 18, the piezo-electric body 17 and the diaphragm 18 are contacted, and simultaneously, the continuity is electrically removed and a piezo-electric vibrator 19 is composed. A metallic case 20 is composed in one body with a fixed part 20a supporting the outer circumference of the diaphragm 18, the cylinder- shaped rise part 20b from the fixed part 20a constructing the front air chamber by facing with the diaphragm 18 and a dome-shaped front air chamber board 20c after that. Plural sound releasing holes 27 are installed at the center of the front air chamber board part 20c, the sound wave oscillated from a vibrator 10 is radiated and the acoustic frequency characteristics are adjusted. The rise part 20b and the front air chamber board part 20c of the case 20 have the effect to heighten the mechanical impedance at the supporting part of the diaphragm 18 and decrease the vibration leakage to the case 20 remarkably.
URA KAZUKI
KAWASAKI KOUZOU
