Development of a high-directivity speaker system for improving sound environment

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15310117
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Social systems engineering/Safety system
• Research Institution: The University of Electro-Communications
• Principal Investigator: KAMAKURA Tomoo The University of Electro-Communications, Faculty of Electro-Communications, Professor, 電気通信学部, 教授 (50109279)
• Co-Investigator(Kenkyū-buntansha): MITSUHASHI Wataru The University of Electro-Communications, Faculty of Electro-Communications, Professor, 電気通信学部, 教授 (40017421) ; AOKI Kenichi The University of Electro-Communications, Faculty of Electro-Communications, Research Assistant, 電気通信学部, 助手 (30017412) ; SUZUKI Hideo Chiba Institute of Technology, Faculty of Information Science, Professor, 情報科学部, 教授 (50333018) ; SAKAI Shinich Mitsubishi Electric Engineering Company Limited, Research chief, 主任研究員
• Project Period (FY): 2003 – 2004
• Keywords: Parametrics speaker / High-directivit / Nonlinear acoustics / Digital envelope modulator / Ultrasound / Audible traffic signal

Research Abstract

Practical development of a parametric array for audio applications has been advanced recently. Actually, most speakers are directional. However, the parametric speaker is directional remarkably. High directivity sound systems having narrow audio beams like a spotlight can transmit a sound to a specific area that cannot be detected by people in adjacent locations. Some new technologies such as appropriate signal processing to improve harmonic distortion are developed in the present research project with an application to an audible traffic signal which provides reliable guidance for going straight across the street. A practical modulation of the carrier ultrasound from an emitter of the speaker is to use the envelope of audio signals such as speech to reduce electric power consumption in working the speaker. First, we have fabricated an envelope modulator with a digital signal processor and made clear that the speaker in working consumes less power with 36% reduction compared with a conventional amplitude modulation. Second, we have focused on improvement of the conversion efficiency from electric power to acoustic power. By connecting an appropriate coil in parallel with the input terminals of the ultrasonic emitter, we were able to reduce reactive current in the emitter, improving the power efficiency reasonably. For speech and music programs, the average electric power was actually reduced by about 30% by connecting the coil. Moreover, the prospective modulation method of SSB with an envelope carrier is discussed to reduce distortion in parametric sounds. Using audible traffic signals emitted from a parametric speaker with sharp directivity are more localizable in a crosswalk than those from a conventional speaker. Last, the use of the parametric speaker has experimentally demonstrated that visually impaired pedestrians can complete the crossing with less getting out of the crosswalk, providing reliable guidance for going straight across the street.