Abstract
Sound absorption performance of needle-punched nonwovens containing polyester fibers of different sizes (7 and 15 denier) and configurations (hollow, 4-hole, hollow conjugated, and hollow trilobal), as well as their composites with perforated rubber layer were investigated. From results, nonwovens of finer 7-denier fibers exhibited higher sound absorption coefficient (a) than that of coarser 15-denier fibers. This was due to greater amount of fibers in nonwovens and larger fiber surface area, thus longer tortuous path for sound waves to travel. Nonwoven of 4-hole fibers (7-4H) showed higher sound absorption performance than that of single hole fibers (7-H) due to increase in surface areas of small holes inside the fibers, thus increasing tortuous path. Likewise, increase in hollow area in the hollow conjugated fibers (15-HC), and angular configuration in the hollow triangular fibers (15-HT) resulted in greater sound absorption coefficient, compared to those of hollow fiber counterpart (15-H). Increasing nonwoven layer to 2 and 3 layers yielded an increase in sound absorption coefficient due to greater thickness and more air gaps between the nonwoven layer. The rubber/nonwoven composites, where perforated rubber layer was inserted between nonwoven layers, exhibited higher sound absorption coefficient in a low- frequency range. This study demonstrated that sound absorption performance could be enhanced through a wide frequency range by employing nonwoven of fine fibers having irregular shapes and large hole area, in combination with perforated elastic rubber.
