Modeling, identification and feedback control of noise in an acoustic duct

We consider a single-input, single-output plant involving one control actuator (speaker) and one control sensor (microphone). Additional speakers and microphones are used to provide disturbances and to assess closed-loop performance. To simplify matters, we confine our consideration in this paper to the case of a collocated sensor and actuator, that is, the control speaker and control microphone located at the same position along the duct. This configuration has been studied in the noise control literature under the name of tightly coupled monopole. In designing feedback controllers for the acoustic duct, we apply modern state space control techniques. The use of such techniques is necessitated by the high order of the identified model, which, for a 400 Hz modeling bandwidth in our experiment, involves 30 states. Feedback controllers designed for noise suppression were obtained by applying LQG synthesis with suitable precompensation to assure robustness to high frequency uncertainty.