Active control of noise in ventilation ducts

Abstract

Ventilation ducts are often lined with passive absorption material for both thermal insulation and noise and vibration reduction. However, the noise reduction performance is not significant at low frequencies. Active Noise Control (ANC) on the other hand can be used in controlling low frequency noise in ducts effectively. This paper presents the main results obtained from the development of an active noise control system for ventilation noise using two approaches. A comparison between the performance of an adaptive feedforward control algorithm and a regenerated reference adaptive algorithm shows that both algorithms provide good noise reduction. Experimental results in the laboratory show that adequate active noise reduction occurs in the frequency range between 100 Hz to 300Hz. The noise attenuation of 20 dB or more for tonal noise can be achieved. The system is also tested in an actual classroom where noise reduction from the ventilation duct is controlled. The results show that the tonal component can be attenuated successfully and a quiet zone achieved in the classroom with a single channel control system