Abstract: 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), and an ultrasonic wave emitting device (300) permanently installed near an area (A101). The ultrasonic wave emitting device (300) emits a first ultrasonic wave towards an area at least including the aforementioned area (A101), and meanwhile, the ultrasonic wave emitting device (100) emits a second ultrasonic wave. The ultrasonic emitting device (100) forms the second ultrasonic wave by means of modulating the ultrasonic wave of frequency f1 with an audible signal.

Abstract: 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), and an ultrasonic wave emitting device (300) permanently installed near an area (A101). The ultrasonic wave emitting device (300) emits a first ultrasonic wave towards an area at least including the aforementioned area (A101), and meanwhile, the ultrasonic wave emitting device (100) emits a second ultrasonic wave. The ultrasonic emitting device (100) forms the second ultrasonic wave by means of modulating the ultrasonic wave of frequency fit with an audible signal.