Ventilation duct silencer design for broad low-frequency sound absorption

Abstract

Low frequency sound absorption in ventilation duct is an important technical issue. In this study, silencer consisting of decoupled annular Helmholtz resonators (AHR) is designed to achieve low frequency sound absorption. The proposed silencer can achieve broadband sound absorption whilst avoiding hindering ventilation. Theoretical model that based on the temporal coupled mode theory (TCMT) is derived to reveal the working mechanism. To improve feasibility of the designed silencer and to reduce the required space for installation, arc-shaped Helmholtz resonator (ASHR) is then proposed as optimisation. Such structure allows the silencer to produce multiple peak absorption frequencies in a smaller dimension. The sound absorption performance of both the structures is investigated numerically and experimentally. For the AHR silencer, measured results indicate a >95% sound absorption coefficient from 690 Hz to 1350 Hz. The ASHR silencer can generate four effective peak absorption peaks over the range 570–1720 Hz. In addition, both structures are installed as the side-branches of the duct, so ventilation condition is completely not affected. The usage of porous materials prevents design process from repeated geometrical parameter tuning and enables continuous operational frequencies. The proposed designs are experimentally verified to possess good feasibility for practical application.