Demodulated sound enhancement based on virtual multi-boosted amplitude modulation with parametric array loudspeaker

Abstract

A parametric array loudspeaker can achieve sharp directivity in the audible band by utilizing ultrasounds. Ultrasounds are emitted intensely from the parametric array loudspeaker and the difference frequency component self-demodulates due to the nonlinear interactions in the air. Therefore, the sound pressure of the audible sound reproduced by the parametric array loudspeaker is lower than that reproduced by the conventional electro-dynamic loudspeaker. This makes it difficult to use the parametric loudspeaker in a noisy environment. To solve this problem, we modify conventional modulations to improve the demodulated sound pressure. When modulated waves are emitted as primary waves, various components containing the audible sound are generated as secondary and tertiary waves. Conventional modulations are difficult to utilize these components of the ultrasonic band effectively. Therefore, we propose the demodulated sound enhancement based on virtual multi-boosted amplitude modulation. In the proposed method, the modulated wave is designed so that frequency components of carrier waves and demodulated sound are generated as the secondary and tertiary waves. Secondary and tertiary waves boost the carrier waves and the demodulated sound, and the demodulated sound pressure can be enhanced. Theoretical value evaluation in the demodulated sound pressure demonstrated the effectiveness of the proposed method.