Low-frequency duct noise control using coupled loudspeakers

Abstract

A duct noise control device is introduced based on a Herschel-Quincke (HQ) tube and electro-mechanical coupling. The device consists of the main duct segment and one set of connected loudspeakers, which functions as a side-by tube in a traditional HQ tube. The acoustic waves imposed on the upstream loudspeaker can be transmitted to the other loudspeaker via the connecting circuit immediately, which represents a fast track when compared with the wave transmission via the fluid medium in the main duct. It is the core noise attenuation mechanism in this silencer. The transfer matrix method is used to investigate the silencer performance. A periodic silencer array is also developed to broaden the bandwidth and increase the magnitude of noise attenuation. The results predicted by the plane wave theory fit well with the simulation using a three-dimensional finite element method. A simplified experiment was conducted to verify the silencing effect of the silencer and the accuracy of theoretical prediction method. Contrasting with a traditional reactive silencer, low-frequency noise attenuation can be achieved in a more compact and flexible way, which can be seen as an improvement in low frequency noise control.