Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/8825
Title: A study of active tonal noise control for a small axial flow fan
Authors: Wang, J
Huang, L
Cheng, L 
Issue Date: 2005
Publisher: Acoustical Society of America
Source: Journal of the Acoustical Society of America, 2005, v. 117, no. 2, p. 734-743 How to cite?
Journal: Journal of the Acoustical Society of America 
Abstract: Sound radiated by a computer cooling fan consists of tones which are phase locked with the rotation, and other less deterministic tones and broadband random noise. This paper demonstrates the feasibility of globally eliminating the rotation-locked tones by applying a very simple destructive interference to a modified cooling fan with the number of struts equal to the number of rotor blades. The rig consists of a miniature electret microphone used as a rotation sensor, an ordinary loudspeaker, and a bandpass filter with adjustable amplitude and phase delay. The microphone is located at the inlet bellmouth of the fan to pick up the fluctuating aerodynamic pressure caused by the passing rotor blades. The pressure spectrum is rich in the blade passing frequency (BPF) and its low-order harmonics. It provides much better performance than a pulse-generating tachometer. Analysis of the original fan noise shows that about 90% of the radiated tonal sound is phase locked with rotation, and this portion is almost completely eliminated in all directions. The reductions of the radiated sound power in the first two BPFs are 18.5 and 13.0 dB, respectively, and the overall sound power reduction is 11.0 dB.
URI: http://hdl.handle.net/10397/8825
ISSN: 0001-4966
EISSN: 1520-8524
DOI: 10.1121/1.1848072
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