Hybrid active and passive noise control in ventilation duct with internally placed microphones module

Abstract

A feedforward active noise control (ANC) system combined with the passive silencer is built to reduce the acoustic noise propagating through the ventilation duct. The passive silencer consists of two layers which are made of aluminum plate and the perforated panels respectively, the cavity between the two layers is filled with the melamine foam. To overcome the two issues encountered in the active noise control for ventilation duct, i.e., the turbulent flow noise and the acoustic feedback, the emphasis of ANC system is the internally placed microphones module. The module is made of a perforated panel shell filled with the melamine foam, the reference and error microphones are both placed in the melamine foam. The real experiments show that the passive silencer has more than 20 dB noise attenuation at frequencies above 600 Hz, ANC can obtain more than 10 dB noise attenuation from 70 Hz to 200 Hz (the maximum 17 dB at 150 Hz) when the wind speed increases from 5 m/s to 10 m/s. In addition, the module is easy to install and maintain, and its manufacturing cost is also acceptable.