Acoustical Test Methods for Nonwoven Fabrics
Acoustical properties of nonwoven fabrics are measured using several different test methods. These important test methods measure physical, mechanical and acoustic properties, which are important for the evaluation, characterization and differentiation of nonwoven fabrics for acoustical applications. Even the basic physical properties of nonwovens play a very important role in acoustics. Physical, mechanical and acoustical properties of nonwoven fabrics are measured using several standards that are defined in ASTM, ISO, ANSI and SAE test standards. Some other measurement techniques that are not included in any standard test methods can also be found in literature. In this chapter, important standard or nonstandard test methods related to acoustical properties of nonwoven fabrics are explained and described. Important physical properties of nonwoven fabrics for acoustical applications are areal density (mass) volumetric density, porosity, particle size distribution, tortuosity and thickness. Density parameters are the most important parameters for the differentiation of the nonwoven fabrics. Porosity also plays a major role in acoustical properties because each pore in the fabric becomes an absorptive material for the sound waves during sound wave nonwoven fabric interaction. Mechanical parameters that are related to acoustical properties of nonwoven fabric are tensile properties and Young's modulus. Acoustical absorption properties of nonwoven fabrics are determined using sound absorption coefficient, sound transmission loss, noise reduction coefficient, sound impedance and airflow resistivity parameters. These parameters could be measured using many different test methods. These methods are explained and related ASTM, ISO, ANSI and SAE test standards are discussed in this chapter. Especially impedance tubes and reverberation rooms are used for most of the acoustical test methods discussed in this chapter.