Active Noise Control of a Plane Sound Wave by a Parametric Speaker

This study investigated active noise control of a plane sound wave by an on-axis parametric speaker. Reducing the sound pressure from a distant noise source is desired in some situations. For example, the sound of dam-discharge warning systems should be reduced in private dwellings near the warning area. Parametric speakers can effectively reduce noises in specific areas. Unlike control by an ordinary speaker emitting spherical waves, the noise control does not increase the sound pressure around the reduction point. The characteristics of the active noise control for a distance noise by the parametric speaker were determined in a numerical simulation and experiment. Compared to standard speaker control, the parametric-speaker control suppresses the sound pressure around the reduction point and widens the reduction area along the central axis. Although the sound pressure of the ordinary speaker changes with distance from the control speaker, the sound pressure of the parametric speaker is reasonably constant along the central axis. Therefore, the sound generated by a parametric speaker is more suitable for suppressing plane sound waves than the spherical waves generated by ordinary speaker.