Effects of pore structure on sound absorption of kapok-based fiber nonwoven fabrics at low frequency

The theoretical relationship between the viscous loss of sound wave and fiber structure parameter (fiber density) and pore structure parameters (pore diameter and porosity) of fibrous absorbing materials has been derived in this paper. Sound absorption of kapok-based fiber nonwoven fabrics with a different pore diameter, porosity or back cavity have been measured by using the impedance tube method. The effects of pore diameter, porosity and air gap on sound absorption at low frequency of kapok-based fiber nonwoven fabrics, caused by the viscous loss of sound waves, have been studied. It is shown that smaller pore diameter or greater porosity yields better sound absorption at low frequency for kapok-based fiber nonwoven fabrics. In addition, the combination of the kapok-based fiber nonwoven fabrics and the back cavity can improve the sound absorption at low frequency of nonwoven fabrics. The sound absorption at low frequency further increased as the back cavity depth increased.