Radiation mode-based personal audio system: Robustness against wall reflection

Abstract

Confining sounds in the near field of a loudspeaker array is discussed for realizing personal audio systems. Active acoustic power propagates to the far field, whereas reactive acoustic power does not. Therefore, increasing the ratio of the reactive acoustic power to the active acoustic power leads to acoustic confinement in the near field. The reactive-to-active ratio is maximized by optimally driving loudspeakers. The optimal driving signals are derived based on the theory of generalized radiation modes. This method was proposed in earlier studies by the authors. In the literatures, point acoustic sources on an infinite baffle were assumed to be in a free space, and the radiation mode theory was applied to obtain the optimal driving signals. However, in practice, walls may exist nearby the loudspeaker array. Acoustic waves radiating from the loudspeakers are reflected by the walls. Such a wall reflection may degrade the acoustic confinement. In this study, the robustness against a wall reflection is investigated.