Abstract
In this paper, an in-depth investigation of the control structures of the active noise cancellation for ducts is presented. The ANC structures of interest are the classical feedback control, feedforward control, and the hybrid control. These ANC structures are compared in terms of performance and robustness by using a general framework of the H ∞ robust control theory. Extensive experiments are conducted to justify the comparison. The advantages, disadvantages, and design considerations indicated in the experimental results for each ANC structure are addressed.