We propose a novel method of three-dimensional spatial audio rendering by expanding the ultrasonic phased array technique. We employ an ultrasonic phased array as a holographic acoustic generator to focus ultrasound at arbitrary three-dimensional positions. The sound pressure at the ultrasonic focal points is sufficiently high to radiate audible sound based on the self-demodulation effect in air. Consequently, the ultrasonic focal points act as audible sound sources. This sound-point method enables us to control aerial audio distributions more flexibly and more precisely in comparison with conventional superdirectional (sound-beam) loudspeakers. This method can generate and vanish the sound sources freely in air. These point sound sources can deliver private messages or music to individuals.
Yoichi Ochiai*, Takayuki Hoshi**
*University of Tsukuba, **The University of Tokyo