Duct Noise Attenuation by Hybrid Control

Abstract

In this paper we present experimental evaluations of hybrid control for duct noise attenuation, with an emphasis on comparing performances of hybrid control to active noise control. A microphone is placed at the downstream of the duct for measuring residue sound pressure level under two different noise control schemes: (1) active noise control scheme uses a loudspeaker for generating an anti-noise, and (2) hybrid noise control which consists of active noise control scheme and semi-active noise control method employing a tunable Helmholtz resonator. It is shown experimentally that for pure tone primary noises in the tested frequency range of 80 Hz to 260 Hz, hybrid control outperforms active control by an averaged 1.5 dB noise reduction. Meanwhile for two-tone primary noises studied by the 15 cases, noise attenuation of averaged 2.6 dB more reduction is observed for hybrid noise control scheme. Finally engine exhaust noises from motorcycles and automobiles are tested for comparison, still the hybrid noise control method apparently has a better performance than the active noise control scheme for noise attenuation.