Spectral Peak Noise Reduction Based on Frequency-Modulated Carrier Wave with Temporal Adaptation for Parametric Array Loudspeaker

Overview & Synopsis

A parametric array loudspeaker (PAL) can realize a sharper directivity by utilizing an ultrasonic wave. Conventionally, the PAL has a problem that ultrasonic transducers cause fatigue failure when the PAL intensely emits an amplitude-modulated (AM) wave for a long time. As a result, the spectral peak noises are generated from the PAL in case that fatigue failure has occurred in ultrasonic transducers. To solve this problem, we have proposed a spectral peak noise reduction using frequency- modulated carrier wave in which the frequency of the AM carrier wave changes with time. The spectral peak noise can be reduced by the previous proposed method. However, the performance is degraded over time in the previous proposed method because it has only initial adaptation even though suitable parameters change with time. In this paper, we therefore propose the spectral peak noise reduction based on the frequency modulated carrier wave with temporal adaptation for the PAL. In the proposed method, the performance maps of the spectral peak noises are measured in advance under the condition that emitting frequency modulated carrier waves with various modulation parameters. The optimal parameter is selected to least spectral peak noise, and the parameter is updated with interval time. Specifically, several parameters are selected in descending order of frequency peak noise reduction using the performance maps. Frequency modulated carrier wave with these selected parameters are emitted from PAL, and the optimal modulation parameter which reduces the most spectral peak noise is determined from the analysis result. Thus, it is possible to continuously reduce the spectral peak noise over time by adaptively updating the modulation parameters at intervals. Finally, we confirmed the effectiveness of the proposed method through experimental experiments.