Acoustic Absorption of Natural Fiber Composites

Table 3

Influence of porous layer thickness on low frequency acoustic absorption of various fibrous and granular materials.

Materials	SAC at = 500 Hz
	Thickness
	10 mm	20 mm	30 mm	40 mm	50 mm
Polypropylene	0.061	0.072	0.080	0.135	0.199
Gravelite	0.066	0.079	0.101	0.138	0.185
Rubber	0.089	0.116	0.220	0.395	0.586
Mineral wool	0.089	0.187	0.401	0.702	0.786
High-silica sand	0.115	0.181	0.319	0.356	0.418