# Development and Characterization of a Flexible Soundproofing Metapanel for Noise Reduction
## 4 Conclusions  
This study demonstrates that the Flexible Soundproofing Metapanel (FSM) offers significant advantages in lightweight design and flexibility while exhibiting excellent sound insulation performance, particularly in specific high-frequency ranges. Our experimental results confirm that the FSM can outperform conventional mass-law-based sound-absorbing materials, especially in high-frequency ranges.  
Figure 8: SPL test for enclosure-type FSM: (**a**) SPL graph comparing the cylinder-shaped FSM with the mass-law control group across 0–8000 Hz. (**b**) Comparison of SPL for the FSM in the target frequency band (2000–5000 Hz) (**c**) Simulated Sound Transmission Loss (STL) of the FSM unit cell compared to the mass law prediction (2000–5000 Hz). Green areas indicate where the FSM’s STL exceeds the mass law, while pink areas show where it falls below.  
We optimized the FSM using urethane rubber with Young's modulus of 6.5 MPa and unit cell dimensions of \(L_{\rm x}=L_{\rm y}=5.5\) mm, \(L_{\rm z}=3.5\) mm, \(t_{\rm f}=0.5\) mm, and \(t_{\rm m}=0.6\) mm. This configuration achieved superior sound insulation performance while maintaining lightweight and flexible characteristics.  
The FSM's flexibility allows its design and application to be tailored to fit the internal structures of products with various shapes and sizes, making it highly practical. This versatility, combined with its effective sound insulation properties, positions the FSM as a promising solution for noise control in diverse applications requiring soundproofing effectiveness and adaptable form factors.  
Our findings present potential applications for FSM in various noise reduction fields, especially in industries such as small electronics, automotive, and aerospace, where weight reduction is crucial. The results open possibilities for achieving both lightweight design and efficient noise reduction simultaneously in product development, potentially improving overall product efficiency across various industrial sectors.  
Future research could explore other materials with superior sound absorption properties or optimize unit cell dimensions to achieve even better performance. This approach could maximize noise reduction effects across a broader frequency range.  
In conclusion, this research demonstrates the FSM's superior performance over traditional mass-law-based materials. It highlights its potential to revolutionize noise control strategies across multiple industries, offering a balance of lightweight design, flexibility, and effective sound insulation.  
Conceptualization, D.J., S.K., J.K., H.K., S.L. and B.K.; methodology, D.J., S.K., J.K., H.K. and S.L.; software, D.J. and S.K.; validation, J.K., H.K. and S.L.; formal analysis, D.J., S.K., J.K., H.K., S.L. and B.K.; investigation, D.J., S.K., J.K., H.K., S.L. and B.K.; resources, B.K.; data curation, D.J. and S.K.; writing--original draft preparation, B.K.; writing--review and editing, B.K.; visualization, D.J., S.K., J.K., H.K. and S.L.; supervision, B.K.; project administration, B.K.; funding acquisition, B.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Hongik University new faculty research support fund.  
Not applicable.  
The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.