OPTIMAL AUDIO BEAM PATTERN SYNTHESIS FOR CONTROLLING THE AUDIO SPOT OF A LENGTH-LIMITED PARAMETRIC ARRAY LOUDSPEAKER

The parametric array loudspeaker has been developed to generate highly directional audible sound in air with a small aperture size compared to the conventional loudspeaker. However, the long propagation distance of the parametric array loudspeaker causes reflections in the indoor application, which disturbs the narrow audio beam reproduction. The length-limited parametric array loudspeaker is an effective way to restrict the audio spot to the near field, but it only controls the length of the reproduced audio beam in the axial direction of acoustic radiation and the audible sound waves leak out in the off-axis direction. ln this work, an optimal audio beam pattern synthesis based on convex optimization is developed and applied to the length-limited parametric array loudspeaker. After synthesizing the audio beampattern of the sub-array, the audio spot is restricted to a narrower area. The numerical simulations based on the Westervelt equation show the proposed method has a better performance with a reduction of 2dB larger than the existing one.