102 Multiple acoustic modes reduction in active control of fan noise

Abstract

To apply an active noise control technique to the fan noise is more complicated than to the plane wave acoustic field, because rotating acoustic modes are generated due to the interaction of stators and rotating blades. In order to achieve the essential elimination of rotating acoustic modes inside the duct, a real-time active noise control system is developed. This system is based on the following techniques; mode decomposition by microphone array, reproduction of rotating acoustic modes by array of loudspeakers and adaptive control using filtered-x LMS algorithm. This paper describes a fundamental study on multiple acoustic modes reduction by this system.