Active noise control using robust feedback techniques

With the resurgence of active noise control in the past two decades, the design and implementation of optimal noise cancellers has been a topic of considerable research. Recently, much of the investigation is focused on fixed controllers that rely on the robustness of closed loop systems to deal with poorly parameterized or changing plants. Many acoustic systems employ internal model controller structures [1-5] designed via H∞ techniques to attain optimality. Absent from the literature, however, is a qualitative study of classical robust controllers applied to the active noise problem. This paper looks at the practical issues and possible pitfalls of applying H∞ optimal feedback controllers to one-dimensional acoustic ducts. In particular, it is observed that the relatively high degree of non-minimum-phase zeros, typical of acoustic plants, limits the ultimate performance of the optimal H∞ solution.