Masato Nakayama

Noise reduction methods have been proposed for various loud noises. However, in a quiet indoor environment, even small noises often cause discomfort. One of the small noises that causes discomfort is noise with resonant frequencies. Since resonant frequencies are often high frequencies, it is difficult to apply conventional active noise control methods to them. To solve this problem, we focused on auditory masking, a phenomenon in which synthesized sounds increase the audible threshold. We have performed several studies on reducing discomfort based on auditory masking. However, it was difficult for comfortable sound design to be achieved using the previously proposed methods, even though they were able to reduce feelings of discomfort. Here, we focus on a pleasant sound: music. Comfortable sound design is made possible by introducing music theory into the design of masker signals. In this paper, we therefore propose comfortable sound design based on auditory masking with chord progression and melody generation to match the peak frequencies of dental treatment noises.

With the development of acoustic simulation methods in recent decades, it has become feasible to simulate the sound pressure distribution of loudspeakers before actually setting physical speakers and measuring the sound field. The parametric array loudspeaker (PAL) has attracted attention due to its sharp directivity and unique applications. However, the sound reproduced by PALs is generated by the nonlinear interactions of ultrasound in the air, which makes it difficult to simulate the reproduced sound of a PAL with low computational load. Focusing on the sharp directivity of ultrasound, we extended conventional acoustic ray-tracing methods to consider the self-demodulation phenomenon of PALs. In this study, we developed a visualization method for the demodulated sound of a PAL. Specifically, the demodulated sound pressure distribution can be simulated to estimate and visualize the area covered by the reproduced sound of PAL before setting a real PAL. In the proposed method, acoustic rays were generated sequentially to express the generation of demodulated sound. Therefore, the proposed method is expected to simulate the demodulated sound of a PAL with acceptable accuracy and low calculation complexity. Quantitative evaluation between simulation results and practical measurement has been carried out, and the results demonstrate the effectiveness of the proposed method.