Patent ID: 8855333

Claim:
An ultrasonic speaker system comprising: a first variable gain block for receiving a speech signal outputted from a speech signal source; a modulation block for receiving the speech signal outputted from the first variable gain block; a second variable gain block for receiving a modulated signal generated in the modulation block based on the speech signal; an ultrasonic actuator that is driven by the modulated signal outputted from the second variable gain block, coverts the modulated signal to an acoustic wave of a finite amplitude level, and radiates the acoustic wave into a medium; and a controller that controls the first variable gain block and the second variable gain block, wherein the controller controls gain of the first variable gain block so that a modulation degree of the modulated signal becomes a predetermined value, when the controller raises the gain of the first variable gain block, the controller lowers gain of the second variable gain block, and when the controller lowers the gain of the first variable gain block, the controller raises the gain of the second variable gain block.