Multivariable control of noise in an acoustic duct

The paper presents a methodology for designing a multi-input, multi-output active noise control system for an acoustic duct. The design technique proposed in the paper begins with measured frequency response data for the duct from which a state space model is constructed using the subspace approach to system identification. Errors between the measured data and the model are taken into account in constructing an uncertain system model for the duct. Then the minimax linear quadratic Gaussian (LQG) control approach is used to synthesize a controller which minimizes the duct noise level at a specified location in the duct. This controller is robust against uncertainties introduced by neglecting the higher order modes of the duct.