Constant-Beamwidth One-Octave Bandwidth End-Fire Line Array of Loudspeakers
Broad-band acoustic signals, such as voice and music, intended for entertainment require uniform coverage over an audience such that the spectral distribution in the area remains constant. Thus the effective beamwidth of the acoustic source needs to be constant with frequency. The ideal solution to array-beamwidth control would be to create a coverage pattern that has one main lobe with small or no sidelobes, with the entire pattern remaining constant with frequency. Such a method for two-dimensional beamwidth control over an octave is presented. The methodology is most flexible and useful when utilizing digital signal processing, since the element responses could be derived with loudspeaker response corrections as part of the synthesis task. The relatively simple algebra of line array superposition yields constant beamwidths very close to theory (when the driver size is accounted for). Considering the strong match with predicted beam pattern, with 20-dB sidelobe suppression for weightings designed for such, this case is presented as a compelling validation of the basic technique.
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