In this study, lightweight membrane-type acoustic metamaterial with flexible and hierarchical structures are proposed to enhance the low-frequency sound insulation performance. Numerical and experimental analyses are conducted on the five models with identical mass in two classes with varying geometries. The sound transmission loss and modal characteristics of the membrane-type acoustic metamaterials are analyzed using the FEM. This analysis provides insight into their acoustic and dynamic behavior in the low-frequency range. The finite element simulation results are validated through reverberant-anechoic testing using a 3D-printed prototypes of the model I and Model II. Modal analysis demonstrated the influences of different geometries on the sound insulation performance. The models with complex geometry (including: Model I, Model II, and Model V) resulted in higher eigenfrequencies in high-order modes, which was caused by their rigidity. In contrast, uniformly spaced eigenfrequencies were observed in some other models including Model III, which exhibited more fluctuations in sound transmission loss across the low-frequency range. Peaks in sound transmission loss mainly occurred around the eigenfrequencies. The first resonance region corresponds to the first eigenmode, resulting in a sharp drop in the sound transmission loss curve. Furthermore, the first peak and the majority of high sound transmission loss values occurred in the anti-resonance regions. Model II presented high sound transmission loss performance in the range of 140–350 Hz, whereas Model I achieved better performance in the range of 350–1500 Hz. Superior performance in Class 2 was achieved by Model V in the ranges of 100–200 Hz and 350–700 Hz. Overall, MAM samples showed an enhancement of 14–22 dBA in sound transmission loss compared to conventional materials, such as rockwool and polyethylene acoustic foam. Statistical calculations show a relatively small difference between the numerical simulation and experimental test. This work demonstrates that lightweight membrane-type acoustic metamaterials can achieve high sound transmission loss in low-frequency ranges without any need to increase the wall mass, through optimized geometrical design.
Khoshru et al. (2026) studied this question.