Active noise reduction in ventilation ducts.

ANC is commonly used in several noise exposed areas. The basic idea has been extensively analyzed in literature, especially for the cancellation of sinusoidal noise in ducts. Here, the challenge for an ANC-system is the attenuation of undesired broadband noise in a ventilation duct with high air flow. In this case special consideration must be given toward the performance of the acoustic sensors while exposed to turbulent flow. The concept of a Swinbank-source in combination with an adaptive filter appears to fit well for the given problem. Furthermore, causality constraints concerning the feed forward adaptive controller are analyzed with respect to sensor and actuator placement. In an experimental setup with a duct of 3 m length and a diameter of 350 mm, noise attenuation of 14 dB in a frequency range from 50