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

Abstract

To achieve global wide‐band noise reduction in a physical acoustic duct, actuating dynamics of the duct were described as two black‐box transfer functions obtained by a hybrid system identification technique. The derived actuating dynamics were then incorporated into a real‐state‐space acoustic duct model for active noise control (ANC). The relative dispositions of two sites, the secondary source and the performance point, along the duct were also investigated to eliminate the effect of lightly damped zeros seen in feed‐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 source. Computer simulation analysis revealed noise reduction of 20 dB or more for periodic disturbance at a fixed frequency within 50–350 Hz, whereas there was 5–17‐dB noise reduction for that within 60–345 Hz in the real experiments. Less noise reduction near both ends of the frequency range (50 and 350 Hz) in experiments might result from the limited frequency range used for the system identification. Global noise reduction was also obtained for disturbances at various frequencies in experiments. In addition, there was effective noise reduction for bandlimited white noise within 50–350 Hz. Taken together, computer simulation and experimental results demonstrate a global wide‐band noise reduction performance.

Key words:

• acoustic duct model
• active noise control
• global wide band
• hybrid system identification

Notes

Correspondence addressee