Least-mean-square weighted parallel IIR filters in active-noise-control headphones

Adaptive filters in noise control applications have to approximate the primary path and compensate for the secondary-path. This work shows that the primary- and secondary-path variations of noise control headphones depend above all on the direction of incident noise and the tightness of the ear-cups. Both kind of variations are investigated by preliminary measurements, and it is further shown that the measured variations can be approximated with the linear combination of only a few prototype filters. Thus, a parallel adaptive linear combiner is suggested instead of the typical adaptive transversal-filter. Theoretical considerations and experimental results reveal that the parallel structure performs equally well, converges even faster, and requires fewer adaptation weights.