In recent years, the demand for reduction of noise emitted into the environment has strongly increased for preventing noise pollution. For example, the ships, which have high noise levels, are refused entry to ports at night. As the major contributor of emitted noise to the environment is exhaust noise, it is necessary to reduce the exhaust noise as much as possible. Conventionally, such as passive silencer technique, a larger silencer is needed in order to achieve larger noise reduction. Therefore, because of the limitation of space, it was actually difficult to reduce the exhaust noise of the ship. For reducing the exhaust noise as well as minimizing the occupied space, the active noise cancellation technique was applied to the exhaust noise silencer for a diesel engine. In order to reduce the exhaust noise efficiently, at first, the acoustic behavior in an exhaust pipe was calculated by the boundary element method. At first, for optimizing the length of pipes and the positions of microphones and speakers, the active exhaust noise cancellation system (AENC) could be applied to the main engine for marine use. Also, by applying acoustic resonance aggressively, the AENC with only one speaker system could be developed for auxiliary engine. The Filtered-X LMS algorithm with a signal filter was used for adaptive control. Finally, by assembling a passive silencer for high frequency noise, the active exhaust noise silencer was developed. Then the exhaust noise was drastically reduced to less than 65dB (A) at 1m from the outlet.
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