Demodulated sound quality improvement for harmonic sounds in over-boosted parametric array loudspeaker

Abstract

The parametric array loudspeaker (PAL) can realize sharp directivity utilizing the straightness of ultrasound, but it suffers from low sound quality due to the frequency-dependent response and harmonic distortions. The reproduces sound by PAL has a low sound pressure because it is generated among nonlinear actions in the air. Therefore, we need to over-boost PAL, which means to drive higher voltage than the standard voltage on PAL, to obtain a higher sound pressure in practical use. However, when PAL is over-boosted, the sound quality degrades due to the increasing distortions. Our goal is to reduce the distortion under the over-boosting. As a result, we can improve the sound quality while keeping high sound pressure. In this paper, we propose a sound quality improvement for over-boosted PAL. We involve voltage adaption in the proposed method so that the sound source is processed with optimized parameters for emitting under a determined driving voltage. In the proposed method, the spectral slope of the sound source is modified to reproduce the original slope in the demodulated sound. And then the spectrum of the sound source is further modified to reduce the harmonic distortions in the demodulated sound. The experimental results demonstrated the effectiveness in both sound quality improvement and over-boost adaptation.