Development of a Highly Directive Endfire Loudspeaker Array
Control of the directivity of loudspeaker systems is important in applications of sound reproduction with public address systems. The use of loudspeaker arrays shows great advantages to bundle the sound in specific directions. Usually, the loudspeakers are placed on a vertical line and the directivity is mainly in a plane perpendicular to that line although the radiation direction can be adapted with filter techniques, called beamforming. In this paper we present results on the applicability of a loudspeaker line array where the main directivity is in the direction of that line, using so-called endfire beamforming, resulting in a “spotlight” of sound in a preferred direction. Optimized beamforming techniques were used, which were developed for the reciprocal problem of directional microphone arrays. Effects of the design parameters of the loudspeaker array system were investigated and we found that the stability factor can be a useful parameter to control the directional characteristics. A prototype constant beam width array system was tested by simulation and measurement and the results supported our findings.
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