Acoustic characterization of natural fibers for sound absorption applications

Natural materials are becoming a valid alternative to traditional synthetic ones for sound absorption treatments. In particular, in recent years, natural fibers have been considered valid raw materials for producing sound absorbing panels at a reduced cost. Moreover, these fibers often have good thermal insulation properties, have no harmful effects on health, and are available in large quantities often as a waste product of other production cycles. Following a literature review of previous studies about the acoustic properties of some natural materials, this paper reports the acoustical characterization of the following natural fibers: kenaf, wood, hemp, coconut, cork, cane, cardboard, and sheep wool. The absorption coefficient and the flow resistance for samples of different thickness have been measured. By using existing theoretical models, this study also compares the measured behavior with the theoretically predicted behavior. This comparison shows the limits of theoretical models originally defined for porous materials with homogeneous fibers, when they are applied to natural materials. Finally, some suggestions for use of these natural fibers for sound absorption applications in buildings are reported.