# Development of Folded Expanded Metal Mesh with Sound Absorption Performance
###### Abstract  
Reverberation time (RT) is an important factor affecting the quality of indoor acoustics. Using sound-absorbing materials is one method for quickly and effectively controlling RT, and installation in the ceiling is a common location. Sound-absorbing ceilings come in many forms, with light steel joint ceilings commonly used in office spaces, classrooms, and discussion rooms. Light steel joint ceilings are often matched with sound-absorbing materials such as gypsum board, mineral fiberboard, rock wool, and coated glass wool, but such materials may have durability and exfoliation problems. Therefore, considering performance and health, in this research, we aimed to design an expanded metal mesh (EMM) structure specimen for sound-absorption material, namely folded expanded metal mesh (FEMM). The results show that the FEMM can significantly improve the sound-absorption performance of the expanded metal mesh. The \(\alpha_{w}\) of single panel is 0.05-0.35, and the \(\alpha_{w}\) of FEMM is 0.65-0.85. On the other hand, the sound-absorption performance of the full frequency band has been significantly improved. Furthermore, the field validation result shows that RT decreased from 1.05-0.56 s at 500 Hz, meanwhile, the sound pressure level (SPL) is still evenly distributed, and speech clarity (\(C_{50}\)) is increased by 5.6-6.5.  
folded expanded metal mesh; ceiling panels; room acoustics +
Footnote †: journal: Applied Sciences  
office space, including sound pressure level, RT, and speech intelligibility, and their results showed that the separation between working seat panels and the installation of ceilings with high sound-absorbing capacity were necessary conditions for better acoustics. For the classroom, many studies have proposed that a comfortable acoustic environment is highly correlated with users' learning ability [6; 7; 8]. [PERSON] and [PERSON] pointed out that being in a noisy environment for a long time has a high correlation with the effect of speech (R\({}^{2}\) = 0.9), indicating that noise will seriously reduce learning ability [9]. In order to achieve full-band sound absorption, most products on the market are manufactured with a multi-layer structure, which contains more than two materials and in turn produces different sound-absorption performances. Such structures then create a wider sound-absorption band [10; 11]; for instance, metal composite materials are often combined with filler material in ceilings [12; 13; 14]. In 1988, [PERSON] [15] proposed a double-layer micro-perforated panel structure, which proved that the sound-absorption characteristics of the said structure were the same as the acoustic resonance structure of a single panel at high frequency, and an additional absorption peak appeared at middle-low frequency. Meanwhile, [PERSON] also pointed out that pore size, perforation rate, thickness, and cavity of the panels affected the sound-absorption coefficient. In recent years, more and more studies have discussed the multi-layer structure and the structure behind the micro-perforated panel. [PERSON] et al. [16] used the sandwich board to carry out sound-absorption coefficient experiments for four specimens and found that the sound-absorption coefficient was effectively improved via the perforated panel. [PERSON] et al. [17] proposed a multi-layer sound-absorption material of the micro-perforated panel that effectively increased the sound-absorption band and the coefficient. Other studies have proposed different shapes of structures in an attempt to increase the support capacity of the specimen while also improving the sound-absorption performance of the material. For instance, [PERSON] et al. [18] proposed to add the concept of origami to the design of the sound barrier. Meanwhile, [PERSON] et al. [19] disassembled a multi-layer structure of the folding panel into multiple units of Helmholtz resonance to calculate the sound-absorption coefficient. However, the manufacturing costs of micro-perforated panels are considerably higher than other materials.