From identification tests carried out in the acoustic duct, see the identification of the cancellation path model, it displays the characteristics of a resonant system. Perhaps a more appropriate control filter would be an infinite impulse response (IR) filter which can model these types of systems more efficiently than the FIR filter. The drawback of these filters though is that they have very poor convergence rate characteristics in conjunction with x-LMS based estimation [2] Adaptive FIR filters in conjunction with x-LMS estimation provides much better performance. Future work will investigate adaptive ANC using IIR control filters but in conjunction with RLS-based estimation.