A parametric loudspeaker—applied examples
Kenichi Aoki, Tomoo Kamakura, Yoshiro Kumamoto · Electronics and Communications in Japan (Part III Fundamental Electronic Science) · 1994
Abstract A parametric loudspeaker using the self‐demodulation of finite‐amplitude ultrasound has a sharper directivity than a conventional loudspeaker of the same aperture size. This is because of the formation of the end‐fire array with virtual sound sources which are generated in the ultrasound beam. In general, when the aperture becomes smaller, the difference in directivity appears clearly. This article describes a theoretical prediction of the optimum frequency of primary ultrasound waves to develop a transmitter with small aperture and compares the theory and experiment using an 11‐cm diameter parametric loudspeaker. The possibility of practical use for guidance equipment such as an audible pedestrian signal also is discussed. Furthermore, using large‐aperture parametric loudspeakers, an experiment is carried out in a reverberant tunnel to confirm the effectiveness in the improvement of speech articulation.