In order to reduce the box volume of so-called bandpass loudspeaker enclosures, a relatively long port is needed. A major problem is then the occurrence of acoustic resonances in the port, resulting in the distortion and coloring of sound. This paper describes a method of eliminating the disturbing resonance peaks, without affecting the efficiency of the system. In a theoretical model, the influence of a branched Helmholtz resonator is outlined, and the resulting measurements concur with theory.
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