Different fiber shapes result in different surface areas; and different surface areas, in turn, lead to different viscous and thermal effects.14 Irregular cross section of fibers also increases the sound absorption due to increased surface area.61 Greater
fiber surface area allows greater sound absorption friction between fibers and air.64 Watanabe et al.64 and Narang et al.65 report a direct correlation between sound ab­sorption and fiber surface area. In the frequency range 1125-5000 Hz, fibers with serrated cross sections absorb more sound compared to ones with a round cross sectional area. Hur et al.66 explain that sound absorption increases with specific sur­face area of fiber with an increase of relative density and friction of the pore wall. Accordingly, Ta§can and Vaughn67 report greater sound transmission loss in fibrous structures of polyester fibers with deep grooves compared to that made from round polyester fibers.

In this regard, biocomposites are advantageous. Plant fiber component of bio­composites generally has increased surface areas caused by their inherent irregular shapes as shown in Fig 5.6 in contrast to smooth surfaces of man-made fibers. This might be the reason for the general acceptance that bio-fibers act as good noise reduction elements.