A duct silencer is used to reduce the noise inside air-handling systems caused by the fan, passage of air through straight ducts, or impact of air flowing through components. The main components for the duct silencer are the resonators. The traditional resonators, generally passive resonators, are specifically designed to achieve their optimal performance at a single frequency, and their effective ranges are limited to a narrow frequency range. Recently, adaptive resonators associated with extra mechanical parts have overcome these drawbacks to some extent, but the large weight and complexity of the whole system might limit their implementation. New designs with simple structures are strongly required for improving the acoustic performance of the duct silencer.