A compact active control implementation for axial cooling fan noise

A multi-channel active control system has been applied to the reduction of free-field tonal noise from a small axial cooling fan, typical of those used in personal computers and other technology. Emphasis has been placed on the development of a compact, practical system, with loudspeakers and error microphones located close to the fan, and which is capable of achieving significant global attenuations for the first four harmonics of the blade passage frequency. In addition, the reference sensor and loudspeakers used have been selected based upon their relatively low cost. Experimental results are presented for five different actuator combinations and tonal meansquare pressure reductions are calculated in each case. A comparison of the performance of each configuration indicates that consistent global control of the four targeted harmonics may be achieved with three control channels.