Robust feedback control of sound radiation into a closed cavity

The field of active noise control is currently very popular due to the fact that it has many practical applications. Some of these applications include decreasing cabin noise in aircraft and automobiles, reducing noise in rocket payload bays, and minimizing machinery noise in factories. Many researchers have developed active control algorithms for vibrating plates radiating sound into free space or enclosures. Most of the controllers employed have been adaptive like the Filtered-x LMS techniques. Very little previous work has been focused on feedback control techniques. In an earlier paper we have described techniques for controlling sound transmission through rectangular plates radiating into a closed cavity. Robust controllers, based on Linear Quadratic Gaussian with Loop Transfer Recovery (LQG/LTR) methods were designed and implemented on simple test articles. In comparison with LMS algorithm, this robust controller did not perform well. The time delay present in the structural system was not considered in the LQG/LTR design method. Hence, a poor performance was the result. In this paper, we have designed and implemented a modified LQG/LTR controller with time delay on an acoustic chamber test article. This controller estimates the previous states from the present output and predicts states for feedback purposes. The time delay of the structure is compensated in the configuration of the estimator of the controller. We have obtained the simulation and experimental results with the modified controller. The performance of the modified LQG/LTR controller is much better than the LMS controller. The performance of the LMS and LQG/LTR controllers is investigated with respect to change in noise frequency and plant parameter variations. The experimental results are included in this paper.