Low-Frequency and Large-Scale Hybrid Sound Absorption Using Active Force Control

Effective low-frequency and large-scale noise reduction are crucial in industrial applications. Conventional passive methods lack the effective low-frequency performance, and existing hybrid methods are costly to realize large-scale absorption. Hence, an effective and simply actuated solution for low-frequency and large-scale absorption is urgently needed. In this study, the low-frequency (100–500 Hz) quasi-perfect absorption characteristics of a hybrid structure which adopts the active force control (AFC) strategy are confirmed by experiment and its large-scale properties are analyzed. By using a flexible plate driven by a concentrated force as the AFC component and a passive MPP absorber, the large-scale model is established to absorb the normally incident plane wave. The structural–acoustic coupling characteristics are analyzed in detail and validated both by the experiment and finite element method. It is observed that by the acoustic–structural coupling, the frequency shift of the first structural mode will be inversely proportional to the total depth of the air cavities. Key parameters relating to the control force and other specifications of the hybrid system are analyzed to improve the broadband performance of the hybrid structure. Owing to the optimized control force, the coupled structural modes could be used to realize commendable large-scale (up to ten times larger than conventional hybrid absorber) absorptions. Compared with conventional methods, the designed absorber is able to realize low-frequency broadband quasi-perfect absorptions while dramatically reducing the number of secondary sources.