The Fundamental Design of Reflective Audio Spot Utilizing Ultrasound Loudspeaker

摘要

Ultrasound loudspeaker which generates higher directivity audible sound waves by the nonlinear interaction between intense amplitude modulated ultrasound waves was focused on research topics, recently. The sound waves which generated with ultrasound loudspeaker have higher directivity as light beam “spotlight” and the area emitted one is called “audio spot”. In addition, acoustic sound image can be produced on the reflecting wall area by reflecting to the wall with ultrasound loudspeaker. Therefore, we try to design reflective audio spot utilizing ultrasound loudspeaker. To realize reflective audio spot, we focused on the sound quality and reflective radiation characteristics of ultrasound loudspeaker. We firstly investigated about sound quality for ultrasound loudspeaker based on amplitude modulation and carrier frequency for a harmonic distortion. As a result of experiments for optimum amplitude modulation and carrier frequency, a harmonic distortion could be suppressed 41 dB by selecting upper band from two single side bands on SSB-AM (Single Side Band Amplitude Modulation) and selecting the resonance frequency as the carrier frequency. We finally investigated about reflective radiation characteristics of ultrasound loudspeaker for acoustic sound image. We especially measured and analyzed the reflective sound energy and reflective radiation characteristics (directional pattern). As a result, we could confirm that the ultrasound loudspeaker was achieved -7 dB sound energy difference between direct and reflect signal, although cone (normal) type loudspeaker was achieved -11 dB sound energy difference between direct and reflect signal. Therefore, we confirmed that the ultrasound loudspeaker was suitable item to realize reflective audio spot.