An adaptive signal processing technique is implemented for the active noise cancellation of the propagating plane acoustic wave in a duct. To avoid the instability caused by the acoustic feedback from the control speaker to microphones, an off-line modeling of the acoustic feedback plant is done, using the FIR filter. Auxiliary path required for the Filtered-x LMS algorithm is modeled as well. Before going into the experiments, a simulation is carried out under the same conditions with experiments. The simulation shows that the longer the length of the adaptive filter is, the better the results are achieved. Experiments have been carried out at lower audio frequency ranges(50~400㎐), the results are in good agreements with those of simulation study. As a results of this adaptive noise control, around 50㏈ is reduced for a pure tone signal, and for a bandlimited white noise input with the bandwith of 316 ㎐, a maximum of 30 ㏈ noise reduction is attained."
