Low frequency sound absorber based on checkerboard Helmholtz resonators with different extended necks

In this study, we develop a checkerboard sound absorber based on Helmholtz resonator with extended neck (HREN), which is capable of low-frequency noise reduction. The absorber is constructed of alternating HRENs with varyinglength extended necks. Based on the transfer matrix method coupled with the equivalent medium method, an analytical model is developed to predict the sound absorption characteristics of the absorber. Its accuracy is validated by the experimental measurements in an impedance tube. Then, we report an analytical and experimental study on the absorption characteristics of HRENs and the checkerboard sound absorbers. Results show that HREN is featured by its thin thickness, and its resonance frequency can be flexibly tuned by designing the length of the extended neck. It is found that the coupling between resonators becomes quite weak if two adjacent resonators in a checkerboard absorber are largely dissimilar. In this case, they operate almost independently, resulting in a dual-band sound absorption performance. A wide-bandwidth absorber can be obtained if two adjacent resonators in the checkerboard absorber are strong coupling. The wide-bandwidth absorber exhibits a quasi-perfect absorption (the absorption coe cient above 0.9) in a wide bandwidth between two absorption peaks induced by two corresponding uniform HRENs. Both the dual-band and wide-bandwidth absorbers still possess the feature of sub-wavelength scale thickness. The proposed checkerboard absorber holds promising potential for low-frequency noise reduction in a constrained space.