Broadband acoustic silencer with ventilation based on slit-type Helmholtz resonators

Recently, sound attenuation with ventilation is highly needed in many practical applications. In this study, we report on a subwavelength acoustic silencer, named double-layer acoustic silencer (DAS), based on compactly assembled slit-type Helmholtz resonators (SHRs) for low-frequency broadband sound insulation while preserving ventilation. A simple yet insightful theoretical model is first established to characterize the sound insulation performance in terms of transmission loss (TL) and used for microstructure designs of the DAS. The fluctuating TL of the DAS, inevitably produced by the SHR resonances, is then mitigated and optimized via the introduction of viscosity and proper SHR frequency detuning. The overall TL is numerically investigated and experimentally observed to reach beyond 30 dB over the target working band of 0.48–0.95 kHz, with a maximum exceeding 50 dB. In addition, the proposed design also provides perfect ventilation when deployed in a duct environment, due to the straight and conserved airflow cross section. We believe that the proposed acoustic silencer design and its associated theoretical model pave the way for designing and optimizing highly efficient low-frequency subwavelength acoustic liners and silencers.