Nonwoven fabrics are ideal materials for use as acoustical insulation products because they have high total surface. The surface area of the fabric is directly related to the denier and crosssectional shape of the fibers in the fabric. Smaller deniers yield more fibers per unit weight of the material, higher total fiber surface area and greater possibilities for a sound wave to interact with the fibers in the structure. Another important parameter is the packing density of the fibers in the nonwoven material. More fibers per unit volume at the same fabric thickness yield greater possibilities for sound waves to interact with the fibers. Fabric density also affects the geometry and the volume of the voids in the fabric structure. Acoustical properties of fabric materials are measured by one of two methods: the impedance tube method (ASTM C 384-98) and the acoustical chamber method. The impedance tube method uses very small test samples. Large reverberation rooms and large test samples are used for the acoustic chamber method. A direct comparative acoustical properties measurement device has been developed and fabricated at Clemson University School of Materials Science and Engineering. This paper provides a description of the measurement devices and acoustical measurement data for needlepunched nonwoven fabrics made from three different polyester fiber shapes and two denier levels.
Acoustical insulation and absorption properties of nonwoven fabrics depend on fiber geometry and fiber arrangement within the fabric structure. The different structures of the fibers result in different total surface areas of nonwoven fabrics. Nonwoven fabrics such as vertically lapped fabrics are ideal materials for use as acoustical insulation products, because they have high total surface. Vertically lapped nonwoven technology consists of carding, perpendicular layering of the carded webs, and through-air bonding using synthetic binder fibers. The surface area of the fabric is directly related to the denier and cross-sectional shape of the fibers in the fabric. Smaller deniers yield more fibers per unit weight of the material, higher total fiber surface area, and greater possibilities for a sound wave to interact with the fibers in the fabric structure. The research in the literature uses two methods for measuring acoustical properties of fabric materials: the impedance tube and reverberation room method. Small test samples are in the impedance tube method and sound absorption coefficient is determined at each frequency. Large reverberation rooms and large test samples are used for the reverberation room method. A direct comparative acoustical properties measurement device that was designed and fabricated at Clemson University School of Materials Science & Engineering was used to measure acoustical insulation in this research. This paper provides a description of the measurement devices and acoustical measurement data for vertically lapped nonwoven fabrics made from three different polyester fiber shape and two denier levels.
This paper deals with ASHRAE filters used in air filtration applications and summarizes, on the basis of current research work, some of the reasons for the disagreement that exists among filter manufacturers concerning the properties and performance of various types of air filter media in general, glass and synthetic media in particular. Attention is also drawn to some important items that need to be incorporated in test methods and to some factors that could be affecting filter performance .
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