Sidelobe suppression by desired directivity pattern optimization for a small circular loudspeaker array

Directivity control using a loudspeaker array is widely studied for various applications. Suppressing sidelobe levels is important for applications such as personal audio systems. In this paper, we propose a filter design method using a window function shape as the desired directivity pattern to reduce the sidelobe levels. The proposed method consists of three steps. The first step defines a cost function with a criterion for the directivity pattern. Next, filter coefficients for each loudspeaker are calculated and stored while changing the window function shape of the desired directivity pattern. Finally, we determine the optimum filter coefficients having the best performance of the cost function by using a full-search algorithm at each frequency. We conducted directivity experiments with a real six-element circular loudspeaker array having a radius of 0.055 m and evaluated its directivity to confirm the performance of the proposed method. The results, which were compared with those obtained from a conventional method, showed that the maximum sidelobe level improved by about 2 dB, although the beam was wide. We verified that using the window function shape as the desired directivity pattern is more effective than using the conventional method for sidelobe suppression.