| Summary: | 碩士 === 國立臺北科技大學 === 機電整合研究所 === 92 === Due to recent development of mobile vehicles, performances of automobiles are increasing and hence the living standard of human being can be lifted. Design of modern vehicles emphasizes not only on driving convenience and performance, but also the quietness and stability. Following the more advanced vehicle development and the higher requirement for living standard, noise emitted from mobile vehicles has become one of the problems affecting the living quality. There are two major noise sources from a vehicle, namely from the engine and its exhaust system. Engine exhaust nose, especially, accounts most of the vehicle noise. By using muffler to absorb or isolate noise at the end of engine exhaust system, noise level can be reduced. However, such a muffler works poorly for noise with frequency under 500Hz. Therefore, it is required to use active muffler for attenuating low frequency noise associated with mobile vehicles.
This thesis uses an active muffler with controller in the form of adaptive filter to reduce the unwanted noise. The low frequency noises (from 50 to 400 Hz) are studied in the experiments, along with mixing noise from both flow field and sound field. Experimental results show that 31.6 dB nose reduction can be obtained for pure tone noise, whereas 16.8 dB reduction for mixing noise signals. This experimental result verifies the effectiveness of using active muffler for attenuating low frequency noises.
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