| Summary: | 碩士 === 國立臺北科技大學 === 機電整合研究所 === 92 === This thesis aims to attenuate duct noise by utilizing hybrid noise control. The hybrid noise control is built by integrating semi-active and active control systems.
In this thesis, the active noise control utilizes an adaptive digital filter as the controller and the adaptive digital filter is a form of IIR digital filter with the Filtered-U Recursive LMS algorithm employed. Feedback control architecture with only one sensor, sound level meter that was placed in downstream of duct is adopted. The semi-active control employs a piston as the Helmholtz Resonator, when the natural frequency of Helmholtz Resonator is tuned to approach the frequency of primary noise, the sound field will be attenuated.
This thesis presents four experimental results. The first part is utilizing genetic algorithm to select the fine-tuned position of piston for Helmholtz Resonator. The average noise attenuation is 13.15 dB which is better than the one with rough-tuned position. The second part aims to attenuate a pure tone by moving the position of piston to the second or third harmonics of the primary noise and followed by activating the active control. The average attenuation is respectively 21.98 dB and 22.76 dB. The third experiment aims to attenuate the noise consisting of two tone signals (one frequency in 100~180Hz and the other in 230~790Hz). The results show that the attenuation of hybrid control is also better than the one of active control, especially for signals with higher frequency. The most amount of noise attenuation compared between active control and hybrid control is 6.5 dB. The last part aims to attenuate engine exhaust noises of automobiles and motorcycles. Experimental results show that the attenuation of motorcycle noise is better than the automobiles. The difference of attenuation for motorcycles between active control and hybrid control is 5.7 dB.
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