Acoustic absorption of fibro-granular composite with cylindrical grains

This paper reports the influence of cylindrical granular materials on the acoustic absorption performance of a natural fiber composite. The acoustic absorption behavior of an innovative fibro-granular composite composed of natural fibers combined with granular materials was investigated. The fibrous part of this new composite is fabricated using coconut coir fiber and the granular part by cylindrical rice husk grain. This study was motivated by a desire to improve the acoustical performance of materials made from natural (coir) fibers. The amount of binder additive added during composite preparation was considered by reconstructing the equation using fiber diameter as a new parameter. The acoustic properties of the novel composite were investigated based on the well-known Johnson-Champoux-Allard model by varying different physical parameters. The experimental analysis was performed in impedance tube to validate the analytical outcome. The developed analytical model employing Johnson-Champoux-Allard model was found to give predictions in good agreement with absorption coefficient data for the composite material samples with four different thicknesses. The effect of varying the different factors, such as sample thickness, fiber–grain size and fiber-grain ratio, on the acoustic absorption performance and the effect of the binder additive were also investigated. Results confirmed the potential of the new material as a promising acoustic absorber in the low-frequency region (less than 1 kHz).