Research on active control of axial flow fan noise using a novel and simplified duct system

Noise from cooling fans is main noise source of the electronic instrument. It consists of rotation noise superimposed by the discrete tones which is related to blade rotation. The aim of present research is to realize the feasibility of using a single loudspeaker to cancel rotation-locked tones with a duct. A photoelectric rotating speed sensor, a loudspeaker which would be located under the PVC pipe and a digital signal processor are employed. An adaptive feedforward system is implemented experimentally to drive the secondary source. The waveform synthesis method is used to adaptively abate noise with traditional least mean square (LMS) algorithm based on steepest descent principle. And simulations have been conducted to verify the convergence and stability of the novel system. Noise characteristics of the cooling fan with/without our active noise controller are compared experimentally. It was found in the experiments that reduction of sound power level is 20dB at the fan's blade passing frequency (BPF) .