This paper is to study the reduction of influence of acoustic feedback on the active control of sound transmission in duct by using two-secondary sources method. Therefore, two parts of the numerical analysis and the active control experiment are included. For theoretical analysis, the optimum distance, phase angle and the strength ratio between the two secondary sources to be used are calculated. In the active control experiment, A FIR filter is to combine with a LMS algorithm to attenuate the acoustic transmission from a primary source in the frequencies from 160 through 600 Hz. The result in this study reveals a very less acoustic feedback generated from the secondary sources influences the detection sensor, and attenuation of more than 30 dB downstream acoustic power at all frequencies to be measured can be achieved.
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