A popular approach for Active Noise Control (ANC) problems has been the use of the adaptive Filtered-X Least Mean Squares (FXLMS) 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 utilized. In contrast with FXLMS a feedback controller utilizes local velocity measurements of a sound-absorbing surface instead of global pressure measurements. Most control problems, including ANC, can be formulated in the General Control Configuration (GCC) 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-infinity and H_2 sub optimal controllers. Such controllers are considered ideal candidates for ANC problems as they can combine near optimal performance with good robustness characteristics. This paper 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 cancelation of the undesired noise can be accomplished. In the paper the H_2 local feedback control strategy and performance are investigated using an experimental pulse tube facility.
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