A unidirectional secondary sound source for local active noise control in enclosures

Abstract

Directional secondary sources are beneficial for local active noise control in cabins with multiple seats. In this paper, a method of designing a unidirectional compound sound source composed of two units is introduced. A prototype was implemented using two closed-box speakers and an analog circuit, and the directivity of the compound source was measured in the anechoic chamber to verify the effectiveness of the proposed design method. Furthermore, the sound radiation characteristics of the compound sound source in a car cabin are reported and analyzed. The average sound pressure level at the driver's seat and rear seats is reduced by over 3.5 dB and 8.3 dB respectively in the frequency range from 125 Hz and 500 Hz when a single loudspeaker box located at the front passenger's seat is replaced by the compound sound source.