ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

2aNS4. Active control of axial-flow fan noise.

John R. MacGillivray

Gerald C. Lauchle

David C. Swanson

Graduate Prog. in Acoust. and Appl. Res. Lab., Penn State Univ., P.O. Box 30, State College, PA 16804

An investigation was conducted using active noise control to reduce noise from small axial-flow fan units commonly found in computers and printers. The fan unit itself was used as the cancellation source in the active noise control scheme, achieved by axially modulating the unit with a shaker. Feasibility studies which looked at radiation efficiency and transfer function data identified fan units which would adequately perform as efficient, undistorted sources of noise when driven by particular shakers. Once a suitable shaker and fan combination was discovered, simulations of active noise control were conducted in MATLAB which utilized the measured error path impulse response (representing the system which defines the output voltage response of a microphone near the fan to an input voltage supplied to the shaker). Results from the simulation showed that an experiment could be constructed which would effectively reduce the tonal components from the fan unit. An experimental demonstration was constructed, results from which show a 20-dB reduction in sound-pressure level for the blade passage tone, a 15-dB reduction for the second harmonic, and a 7- to 8-dB reduction for the third harmonic. [Work supported by IBM through Shared University Research Program.]