Barrier-free duct muffler for low-frequency sound absorption

We demonstrate a duct muffler design that operates in the low-frequency range (<2000 Hz). The device contained pair of coupled annular Helmholtz resonators (HRs) and porous material stuffing. HRs were installed as side branches circular tube to avoid affecting ventilation. Porous materials employed form an asymmetric intrinsic loss HR enable achieve perfect sound absorption. An analytical model based on temporal coupled-mode theory was derived, numerical simulation technique for structural introduced verified. experimental study demonstrated effectiveness methodology illustrated can near-perfect absorption desired frequency range. A symmetrical configuration also experimentally proved be able conduct incident from both sides duct. This provides solid foundation application designed explanation corresponding mechanisms.