A novel gradient multi-Helmholtz cavities muffler for low-frequency broad bandgaps

We proposed a gradient multi-Helmholtz cavities muffler for low-frequency broad bandgaps. The simulation and experiment results of our analysis claimed that this structure can reduce noise in resonance frequency, and the range of absorption frequency is enlarged with the number of cavities increase, almost 24.75 times that of one cavity. The transmission loss around the center frequency also increases from 45[Formula: see text]dB to 100[Formula: see text]dB. In addition, the relationship between noise attenuation and the distance of the cavities is also studied. Results show a deeper valley appears in the transmission loss curve with an increase of the distance, which greatly affects the sound absorption performance.