| Summary: | 碩士 === 國立臺灣海洋大學 === 系統工程暨造船學系 === 94 === Abstract
The purpose of this paper is to proceed active noise control (ANC) experiment in duct and free-field sound space using the adaptive filter theory with digital signal processor (DSP) TMS320 C6713 DSK (DSP Starter Kit) . We first eliminate the noise in electric signals to realize the fundamental principle of adaptive control, that is, we write two componential elements of the adaptive filter, filter structure (FIR) and adaptive algorithm (LMS), into program with C language. Then we use real-time DSP as the core of whole hardware structure and transform the continuous analog sound signals into discrete digital ones. Finally, we can attain the required signals using the control algorithm.
Then we proceed to research the ANC of sound field for 1-D square duct and 3-D ideal open space (anechoic room) field. Afterwards we discuss many ANC factors that we didn’t take into consideration in electric noise elimination, such as the influence of the second path, acoustic field feedback, system identification and the frequency response of the loudspeaker. Therefore, we change algorithm into FXLMS method considering the second path. Before experiments, we first do system identification. We also use different sounds to simulate noise source. Pure tone, dual sine signal, and band noise are eliminated with the control experiments in 1-D duct and 3-D ideal open space. The result shows that the noise reduction of the narrow and broad band frequency can be obtained. In 1-D duct, pure tone has the effect of average 60dB noise reduction; dual sine signal has the effect of over 40dB noise reduction. In band noise, the individual average value of noise reduction are 32dB、26dB and 11.5dB in bandwidth 25Hz、50Hz and 100Hz respectively. In 3-D ideal open space, pure tone has the effect of average 50dB noise reduction ; dual sine signal has the effect of over 40dB noise reduction. In band noise, the individual average value of noise reduction are 33dB、31dB and 32dB in bandwidth 25Hz、50Hz and 100Hz respectively. Confirmed by the result, C6713 DSK can be used as the workbench for the initial programming simulation and experiment design of ANC commercialization.
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