Discrete-Time Parametric Modeling of Loudspeakers Used for Active Noise Control in Long Narrow Ducts

The secondary path in active noise control systems is generally consisted of electromechanical (loudspeakers) and acoustic elements. The secondary path is substantial part of any active noise control system. For adaptive systems, it influences on its convergence properties. For nonadaptive, it makes an additional term in control chain that can cause instability in closed-loop control. If the duct is long enough, the system will cancel the propagating acoustic wave before it reaches the end. This fact allows us to use infinite acoustic waveguide model for the duct, and to estimate loudspeaker acoustic load in such a way. The loudspeaker itself is modeled using electro-mechanical analogies, and obtained continuous-time model is transferred in z-domain using bilinear transformation. Proposed method can be made to include finite-length waveguides.