A nested multistage sonic black hole structure: Design, optimization, and experimental validation for duct noise control

A nested multistage sonic black hole (MSBH) structure is developed to attenuate broadband low-frequency acoustic waves, particularly under open-end conditions. A theoretical model based on the transfer matrix method (TMM) is established and shows good agreement with finite element simulations. The sound attenuation mechanisms of structures incorporating sonic black holes and their extensions are further investigated. Results indicate that the MSBH structure provides effective sound attenuation and enhances low-frequency sound absorption. Crucially, it significantly improves low-frequency sound insulation performance even under open-end conditions. Multi-objective particle swarm optimization is subsequently employed to optimize the design parameters of the MSBH system with the open end, aiming to achieve compatibility between sound insulation and absorption requirements. The optimized five-stage MSBH design achieves an average absorption coefficient of 0.54 and an average sound transmission loss of 22.18 dB over the 10–200 Hz range, demonstrating a well-balanced trade-off between sound absorption and insulation. Impedance tube experiments conclusively validate the model and demonstrate the structure’s effective broadband low-frequency attenuation. The proposed open-ended MSBH structure is thus suitable for duct systems with open terminals, such as those in high-speed trains and ship cabins.