| 摘要 |
PROBLEM TO BE SOLVED: To provide a system that can create an audible sound filed at an optional point in a space without the need for a mechanical drive mechanism. SOLUTION: Two speakers 11, 12 emit ultrasonic waves whose frequency f1 is the same but whose phases differ from each other so as to create an intense linear ultrasonic wave sound field only in a particular direction (shown in dotted lines) through the interference between them. Similarly two speakers 21, 22 emit ultrasonic waves whose frequency f2 is the same but whose phases differ from each other so as to create an intense linear ultrasonic wave sound field only in a particular direction (shown in dotted lines) through the interference between them. When a difference between the frequencies f1, f2 is selected to be a frequency within an ultrasonic wave band (20 kHz or over), an ultrasonic wave sound field with a frequency f3=|f1-f2|is created only at cross points of both the interference ultrasonic wave sound fields (auditory area). When other ultrasonic wave speaker 31 emits an ultrasonic wave resulting from superimposing an audible sound wave on the ultrasonic wave with the frequency f3, an audible tone by beat can be created in the auditory area.
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