Patent ID: 6384550
Filing Date: 2002-05-07
Classification: H04R

Abstract:
A speaker comprising:inputting means for inputting a sound signal; a diaphragm for outputting sound; a supersonic motor having a mover and a stator, said stator including a piezo-electric material having a number of electrodes to which vibration wave signals are supplied to cause motion of said piezo-electric material, the motion of said stator being transmitted to said mover; connecting means for connecting said mover to said diaphragm; detection means for detecting a position of said mover so as to generate current position information; differentiation means for differentiating the position information so as to generate current speed information; comparison means for comparing the current position information and desired position information defined by the sound signal so as to operate a difference between the current position information and the desired position information corresponding to desired speed information in a digital form; limiter means for limiting the difference in the digital form so that the desired speed information does not exceed a maximum speed of said supersonic motor for driving said diaphragm; drive means for generating the vibration wave signals to drive said supersonic motor; and control means for controlling an amplitude and a frequency of the vibration wave signals in accordance with a difference between the current speed information and the desired speed information limited by said limiter means.