SOUND GENERATION SYSTEM, ULTRASONIC WAVE EMITTING DEVICE, AND ULTRASONIC WAVE EMITTING METHOD

摘要

Disclosed are a sound generation system, an ultrasonic wave emitting device, and an ultrasonic wave emitting method which utilize the principle of parametric speakers (which uses the difference between frequencies of two ultrasonic waves) and which are capable of allowing target persons in a prescribed area to hear a sound only when a mobile body approaches said prescribed area. An alert system (10) has an ultrasonic wave emitting device (100) mounted on a mobile body (200) (for example, a vehicle such as a car), and an ultrasonic wave emitting device (300) permanently installed near an area (A101). The ultrasonic wave emitting device (300) emits a first ultrasonic wave (frequency f1) towards an area at least including the aforementioned area (A101), and meanwhile, the ultrasonic wave emitting device (100) emits a second ultrasonic wave (frequency f2). The ultrasonic emitting device (100) forms the second ultrasonic wave by means of modulating the ultrasonic wave of frequency f1 (that is, an ultrasonic wave the similar to the first ultrasonic wave) with an audible signal.