Actuator placement and zero effect on global wide-band noise reduction in ducts with hybrid system identification technique

To achieve global wide-band noise reduction in a physical acoustic duct, ac tuating dynamics of the duct were described as two black-box transfer funct ions obtained by a hybrid system identification technique. The derived actu ating, dynamics were then incorporated into a real-state-space acoustic duc t model for active noise control (ANC). The relative dispositions of two si tes, the secondary source and the performance point. along the duct were al so investigated to eliminate the effect of lightly damped zeros seen in fee d-forward ANC design. A better performance was obtained when the two sites were far apart and the secondary source was near to the primary noise sourc e. Computer simulation analysis revealed noise reduction of 20 dB or more f or periodic disturbance at a fixed frequency within 50-350 Hz, whereas ther e was 5-17-dB noise reduction for that within 60-345 Hz in the real experim ents. Less noise reduction near both ends of the frequency range (50 and 35 0 Hz) in experiments might result from the limited frequency range used for the system identification. Global noise reduction was also obtained for di sturbances at various frequencies in experiments. In addition, there was ef fective noise reduction for bandlimited white noise within 50-350 Hz. Taken together, computer simulation and experimental results demonstrate a globa l wide-band noise reduction performance.