Forbidden Transmission of Broadband Duct Noise Realized by Compactly Placed Detuned Resonators

Effective broadband duct sound propagation control is highly required in many practical engineering applications. In this study, a compact structure constituted by multiple detuned resonators is proposed for broadband duct noise transmission control. The coupling characteristics of two detuned resonators flush-mounted on the sidewall of a duct are firstly investigated. Results show that a coherent perfect absorption (CPA) is induced when these two resonators are precisely designed. Meanwhile, a nearly flat transmission forbidden band is formed, which is very beneficial for duct noise control. Furthermore, it is found that the appearance of the forbidden band is insensitive to the distance between resonators. On this basis, a customized broadband CPA-based structure constructed by detuned resonators is developed, in which the geometric parameters of each adjacent resonator satisfying the CPA condition and the resonators are closely placed. By overlapping the forbidden band of adjacent resonators, a broad duct sound transmission forbidden band is attained. The acoustic performance of the proposed compact design is demonstrated experimentally.