Directive drivers spatially filter out array side lobes that would otherwise alias.

Evidence

One way of reducing the effect of spatial aliasing is to use directive loudspeakers instead of point sources as the array elements. If one uses directive sources, their polar patterns will act as a form of spatial filter. That is, the off-axis side lobes will be reduced by the off-axis reduction in sound level that a directive source affords. Figure A6.7 shows an array response at 10kHz (kd = 7.85) with the response of a continuous line source, of length equal to the element spacing, superimposed upon it. Of particular note is that the zeros of the continuous line source fall on the aliased main lobes from the point source array. Because the farfield polar pattern of an array of point sources is related to the applied signals by a Fourier transform relationship, all the theorems that apply to the discrete Fourier transform apply to the array loudspeaker. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2907

Categorization

• XREF: Connects to the Fourier transform duality between array spacing domain and angle domain — mirrors sampling-theory aliasing in DSP, familiar from digital audio concepts.