Two driving constructions of loudspeakers for low‐frequency range by piezoelectric ultrasonic motors.

Abstract

The loudspeaker driven by piezoelectric ultrasonic motors is characterized by a precise very‐low‐frequency reproduction due to its high‐driving mechanical impedance. It has a lot of merits comparing to the conventional electrodynamic loudspeakers. One of the reason will be that this loudspeaker is a power flow modulator, not a transducer. In this presentation, two sorts of ultrasonic motors are compared as driver elements of the loudspeakers. One is an ordinary revolution‐type motor and the other is a reciprocal linear motion type actuator. The authors constructed and improved practical low‐frequency‐range loudspeakers by using continuous revolution of ultrasonic motors. Its final model uses combination of two motors with same axis, which drive two cone radiators moving oppositely. This model shows a satisfactorily large output sound pressure and stable reproduction. However, its complicated elements for connection of the motors and the cone radiators cause a mechanical weakness. The authors, therefore, p...