Synchronized amplitude-and-frequency modulation for a parametric loudspeaker

Parametric loudspeakers have very high directivity and can be applied to various applications. In such loudspeakers, modulating the carrier waves is important because the modulated waves are demodulated into audible waves by nonlinear interaction in the air. Amplitude modulation (AM) has been proposed as the modulation method for parametric loudspeakers and frequency modulation (FM) has been empirically utilized for them. However, FM has been insufficiently studied because it has been considered as one type of amplitude modulation for parametric loudspeakers. In this paper, we reveal that the demodulation in AM and FM differs in a parametric loudspeaker. In addition, we propose a new modulation method based on synchronized demodulation of AM and FM. The method achieves higher sound pressure levels at lower frequencies than conventional modulation methods. Finally, we confirm the method's effectiveness through evaluation experiments.