Method of controlling output of ultrasonic speaker, ultrasonic speaker system, and display device

An ultrasonic speaker system having a signal source that generates signal waves in an audible frequency band, a carrier wave supply unit that generates carrier waves in an ultrasonic frequency band, and an ultrasonic transducer that modulates the carrier waves with the audible-frequency-band signal waves output from the signal source and is driven by the modulated waves, comprising:

• a plurality of filters that divide the audible-frequency-band signal waves into a plurality of frequency bands;
• a plurality of signal wave amplitude adjustment units that separately adjust amplitudes of the signal waves in the respective frequency bands;
• a plurality of modulation units that modulate the carrier waves with the signal waves in the respective frequency bands;
• a plurality of modulated wave amplitude adjustment units that separately adjust amplitudes of the modulated waves output from the plurality of modulation units;
• a plurality of ultrasonic transducers driven by output signals of the plurality of modulated wave amplitude adjustment units;
• band-corresponding volume setting units that are provided corresponding to the respective frequency bands and separately set volume of the ultrasonic transducers corresponding to the respective frequency bands;
• an overall volume setting unit that sets volume in common with respect to all of the ultrasonic transducers corresponding to the respective frequency bands;
• and
• modulated wave amplitude gain control units provided corresponding to the respective frequency bands that, in the respective frequency bands, receive band-corresponding volume setting data indicating states of the band-corresponding volume setting units and overall volume setting data indicating a state of the overall volume setting unit and determine gains of the modulated wave amplitude adjustment units provided corresponding to the respective frequency bands on the basis of a combination of the band-corresponding volume setting data and the overall volume setting data when adjusting amplitudes of the modulated waves generated in the respective frequency bands.

A display device comprising:

• an ultrasonic speaker that reproduces audible-frequency-band signal sounds by modulating ultrasonic-frequency-band carrier wave signals with audible-frequency-band signal waves supplied from a sound source and driving an electrostatic ultrasonic transducer with the modulated signals;
• and
• a projection optical system that projects an image onto a projected surface,
• wherein the ultrasonic speaker includes:
• a plurality of filters that divide the audible-frequency-band signal waves into a plurality of frequency bands;
• a plurality of signal wave amplitude adjustment units that separately adjust amplitudes of the signal waves in the respective frequency bands;
• a plurality of modulation units that modulate the ultrasonic-frequency-band carrier waves with signal waves in respective frequency bands output from the signal wave amplitude adjustment units;
• a plurality of modulated wave amplitude adjustment units that separately adjust amplitudes of modulated waves output from the plurality of modulation units;
• and
• a plurality of ultrasonic transducers driven by output signals of the plurality of modulated wave amplitude adjustment units.