Abstract
The objective of this study is to explore two approaches of noise control for ducts: the passive control and the active control. The passive approach which is conventional consists mainly of design of mufflers, based on acoustic filter theories. The active approach, on the other hand, particularly useful for low-frequency ranges. The active noise controller is implemented by a fixed-point digital signal processor which provides great computation power as required by the adaptive control for the frequency range of interest. The performance of the active control and passive control systems are compared in a series of experimental investigations. Synthetic noises in laboratory as well as practical exhaust noise from an automobile engine are chosen to test both techniques. In contrast to the passive control method, the experimental result shows excellent performance of ANC method in attenuating low-frequency noise. Criteria of choosing control parameters are also summarized.