Zero/pole placement control of periodic duct noise

A zero/pole placement controller (ZPPC) is presented here for active control of periodic duct noise. It uses sound pressure feedback instead of modal feedback. The controller is able to place closed-loop zeros in addition to closed-loop poles. A new adaptation law is proposed to help the controller to track parameter drifting and maintain good performance. The controller can combine with any feedforward scheme to form a hybrid (feedforward/feedback) active noise controller. It has an advantage of on-line identification of the secondary path without persistent excitations.