Recently, a parametric loudspeaker that demodulates an ultrasonic wave passed through amplitude modulation (AM) or frequency modulation (FM) by using a density phenomenon of air to reproduce audible sound has been developed.
In the parametric loudspeaker, the ultrasonic wave is used. Thus, it is possible to realize an audio device with a high directionality. With the audio device with the high directionality, for example, it is possible to propagate sound to only a specific user, thereby making it possible to provide saleability such as privacy protection. Further, for example, it is possible to provide a function of propagating sound to only a specific position.
In order to control an output direction of a sound output from the parametric loudspeaker, a phased array method is used, for example. In the phased array method, ultrasonic waves oscillated according to a change in timing from an array vibrator in which a plurality of ultrasonic wave vibrators is arranged are combined to oscillate a main beam.
Recently, as a mobile phone as mentioned above, various techniques have been proposed (Patent Documents 1 and 2).