This paper presents a method for designing a DSP controlled directional array speaker with constant directivity and specified sidelobe level over the wideband frequency by means of the two-dimensional (2-D) Fourier series approximation. The band of constant directivity can be extended in the lower frequency band by using the non-physical area in the 2-D frequency plane, where the target amplitude response of the 2-D filter is set to design the 2-D FIR filter. We discuss that the beamwidth of the array speaker can be narrowed in the more lower frequency band with a modification of the original algorithm by K. Nishikawa, et al.
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