Acoustic Absorption Performance of Coir Fiber- Rice Husk and Coir Fiber-Polystyrene Fibro-Granular Composites

Coir fiber and rice husk are two cost effective, abundant, sustainable and eco-friendly natural waste materials. Both of these natural waste substances have potential to be utilized as effective acoustic absorbers for various building and automotive applications. Polystyrene is also an eligible conventional sound absorbing material, which are identical and spherical shaped. The influence of granular materials on the acoustic absorption performance of a natural fiber composite was investigated in this study. This paper aimed to discuss the sound absorption properties of two innovative fibro-granular composites composed of natural fibers combined with natural and conventional granular materials. The fibrous and the granular components of one composite are pure natural which are fresh coir fiber and rice husk. On the other hand, the fibrous component of other composite is natural coir fiber and granular part is expended polystyrene beads. The amount of binder additive and grains added during
composite preparation were compensated by reconstructing the equations using fiber diameters as new parameters in the case of both composites. The compensation was also considered for other two geometrical parameters such as porosity and viscous characteristic length, in order for the formulation of analytical model. The prediction of the sound absorption coefficient was performed in terms of developed analytical model by employing rigid frame Johnson-Champoux-Allard model. The experimental analysis was conducted through impedance tube measurement in order to support the analytical outcomes. Both analytical and experimental analyses were performed at different thicknesses for each composite sample. Results confirmed the potential of the coir fiber-rice husk composite as a better and promising acoustic absorber than the coir fiber-polystyrene in the low-frequency region (less than 1 kHz).