Noise suppression using local acceleration feedback control of an active absorber

Abstract

A popular approach for active noise control problems has been the use of the adaptive filtered-X least mean square algorithm. A fundamental problem with feedforward design is that it requires both reference and error sensors. In order to reduce the size, cost and physical complexity of the control system, a feedback controller can be utilised. In contrast to filtered-X least mean square, a feedback controller utilises local acceleration measurements of a sound-absorbing surface instead of global pressure measurements. Most control problems, including active noise control, can be formulated in the general control configuration architecture. This type of architecture allows for the systematic representation of the process and simplifies the design of a vast number of controllers that include $H_{\infty }$ and controllers. Such controllers are considered ideal candidates for active noise control problems as they can combine near-optimal performance with good robustness characteristics. This article investigates the problem of reflected noise suppression in acoustic ducts and the possibilities and trade-offs of applying $H_2$ control strategies. Hence, by controlling locally the reflecting boundary structure, a global cancellation of the undesired noise can be accomplished. In this article, the $H_2$ local feedback control strategy and performance are investigated using an experimental pulse tube. The $H_2$ design was chosen because it was able to provide consistently a stable response in contrast to the design.