Investigation on sound absorption properties for recycled fibrous materials

Acoustic is currently one of the most important fields of study. Recently, many studies have been carried out in this field and new findings have uncovered the potential use of new materials for sound absorption applications. This paper investigated the sound absorption properties for recycled fibrous materials including natural fibers, synthetic fibers and agricultural lignocellulosic fibers. Nonwovens produced from recycled natural fibers blended with synthetic fibers have been tested acoustically. Also, biocomposites from agriculture wastes such as rice straw and sawdust have been investigated. The results indicated that nonwoven samples have high sound absorption coefficients at high frequencies (2000–6300 Hz), low sound absorption coefficients at low frequencies (100–400 Hz) and better sound absorption coefficients at mid (500–1600 Hz) frequencies. The sound absorption coefficients at all frequency ranges improved by increasing the thickness of nonwovens. Also, adding air space behind the sample improved the sound absorption at low and mid frequencies. The tested rice straw and sawdust composite samples achieved low sound absorption at low and mid frequencies. However, they have slightly high sound absorption at high frequencies. A significant improvement in sound absorbing performance at low, mid and high frequencies was achieved by adding perforation of 6% for the tested sample and increasing the thickness of nonwoven samples. Adding air spaces behind the tested composite systems could improve the sound absorption at low and mid frequencies. Generally, the results indicated that recycled fibrous materials hold promise for use as raw material for sound absorbing, being low cost, lightweight and biodegradability.