Virtual multi-boosted amplitude modulation toward high-pressure audible sound with parametric array loudspeakers

A parametric array loudspeaker (PAL) can achieve sharp directivity in the audible band by using ultrasounds. Ultrasounds are emitted intensely from a PAL, and the difference frequency component self-demodulates because of nonlinear interactions in the air. As a result, the sound pressure of the audible sound reproduced by a PAL is lower than that reproduced by a conventional electro-dynamic loudspeaker. This makes it difficult to use a PAL in a noisy environment. To solve this problem, we modify conventional modulations to improve the demodulated sound pressure. When the amplitude-modulated wave is emitted as a primary wave, distortion of the primary wave generates various components, including the audible sound, as higher-order components. Conventional modulation methods have difficulty using these components of the ultrasound band effectively. Hence, we propose virtual multi-boosted amplitude modulation toward high-pressure audible sound with PALs. In the proposed method, the modulated wave is designed so that frequency components of the carrier waves and the demodulated sound are generated as the higher-order components, which are the distortion components of the primary waves. These components can boost the carrier waves and the demodulated sound, thus increasing the demodulated sound pressure. The effectiveness of the proposed method is demonstrated by comparing the audible sound pressure of the proposed and conventional methods.