Abstract
<title>Abstract</title> <p>The sound absorption and transmission characteristics of coir composites and coir-plywood composite panels are investigated in this paper. Natural composites made of coir fibres with poly vinyl alcohol (PVA) as matrix is used in the experiment. Samples of different thicknesses, fibre lengths, and fibre-matrix compositions are tested to obtain the optimal fibre size, composition and panel thickness that gives the maximum sound absorption coefficient. The optimized coir composite, which shows the maximum noise attenuation characteristics, is used for making coir-plywood composite panels. These panels with different configurations such as i) coir lamina facing the sound waves ii) plywood part exposed to sound and iii) sandwich models in which coir is placed in between two plywood panels are tested for their sound absorption and transmission properties using an impedance tube. The results show that the stacking sequence of the coir and plywood in a coir-plywood composite panel significantly influences the sound absorption coefficients, while the transmission loss is not much affected. These findings can have great applications in noise control fields, especially in the design and development of noise enclosures for machines and personnels.</p>