Adaptive-passive noise control with self-tuning Helmholtz resonators

A tunable Helmholtz resonator and a novel feedback based control law that achieves optimal resonator tuning for time varying tonal noise control applications are presented in this paper. The proposed tuning strategy combines an open loop tuning algorithm based on a simple lumped parameter model of the resonator with a gradient descent approach based on a feedback control structure that ensures robust performance. Optimal tuning of the resonator is achieved despite system uncertainties such as variations in the excitation frequency and environmental changes. An experimental verification of the proposed control law is included. Sound pressure level reductions of up to 30 dB were achieved in an experimental duct system using a tunable Helmholtz resonator. (C) 1997 Academic Press Limited.