Acoustic reflector utilizing sound speed control by multiple obstacles

Acoustic diffusers have a structure that diffuses sound waves in various directions by utilizing the interference of sound waves caused by surface irregularities. For example, a phase diffraction grating based on number theory has a structure with equally spaced depressions of irregular depth, and the maximum difference between the depressions is half the target wavelength. If the reflector targets 500 Hz sound waves, the thickness of at least 34 cm is required. On the other hand, the acoustic lens proposed by Kock et al. in the 1950s composed by multiple spheres or other obstacles to control the speed of sound. This report proposes a diffuser without depressions of irregular depth by applying the acoustic lens principle of Kock etal. The difference in reflection time caused by the depressions of the diffuser can be controlled by multiple obstacles.