Implementation of coir fiber as acoustic absorber material

Abstract

Coir fiber is one of the natural fibers that can be easily found in tropical countries like Malaysia. This study illuminates the acoustical absorption of coir fiber throughout the frequency spectrum. The empirical Delany-Bazley method together with Allard elastic model were the two analytical approaches implemented in this research. Outputs of analytical techniques were validated by impedance tube measurements. Both methods were able to show the general pattern but existing frame resonance/resonances could only be predicted by Allard model as Delany-Bazley method does not take modulus of elasticity into consideration. Absorption of fresh coir fiber was satisfactory; more than 70% at f>600 Hz for a 30 mm thickness sample with resonance peak center frequency at 1 kHz. The industrial prepared coir fiber is mixed with binder; has higher stiffness and contains less amount of moisture compared to fresh samples. Therefore the absorption of industrial prepared fibers with the same thickness were generally less than 70% except for a small region around its resonance peak which also happened at higher frequency of 2.6 kHz. It is suggested that absorption of the industrial samples should be improved further in order to be used in real world applications.