Effect of Compression on the Acoustic Absorption of Coir Fiber

Problem statement: The absorption characteristics of coir fiber were analyzed previously. Analytical method to predict the acoustical behavior of coir fiber has already been developed. However, compression effects of coir fiber were not explored which might significant for acoustics absorption during seat padding. In this study, compression effect on the sound absorption characteristics of coir fiber are demonstrated based on the previous analytical approach such as rigid frame method with the modification in the physical parameters. Approach: The verification of the estimated acoustical absorption coefficient in uncompressed condition using rigid frame Johnson- Allard Model are shown for three different thicknesses of industrially processed coir fiber mixed with binder latex. Measurements were conducted in impedance tube on normal incidence sound absorption of coir fiber. It is well known that the absorption behavior of a porous material varies during compression and affects the physical parameters. In these analyses, formulas proposed by Castagnede are employed to predict the compression effect on the absorption of coir fiber which takes into account the modifications of the physical parameters during compression. Results: The agreement between the analytical and measured results is justified for all three sample thicknesses in uncompressed condition. Analyses on the acoustic behavior of material during compressed condition show that compression has a substantial effect on the absorption of coir fiber. It also indicates that the absorption of coir fiber can be enhanced by compressing the material. In addition, the absorption performances are compared by varying the compression rate on material at uncompressed and compressed condition. Conclusion: From overall analyses, it is evident that compression of coir fiber can significantly change the absorption behavior of coir fiber from the actual acoustical characteristics as estimated at normal condition. Moreover, compressing the material might be considered as a possible approach to improve the absorption coefficient of coir fiber. An additional example is presented to show a potential way of enhancing absorption coefficient of coir fiber utilizing compression effect.