Acoustic Properties of Multi-Layer Wool Nonwoven Structures

Wool insulating materials provide good acoustic insulation and are increasingly used for room insulation. These insulating materials are usually produced using nonwoven techniques. The structure and nonwovens parameters affect the acoustic properties of the product. During the investigation, acoustic properties of needle punched and stitch-bonded wool nonwovens were examined. Sound absorption coefficient and noise reduction coefficient for monolayer and multi-layer structures were determined. Relations between acoustic characteristics and nonwoven thickness, surface density, and air permeability were revealed. For the multi-layer structures, an increase of sound absorption with an increase in layer numbers was observed. The increase in sound absorption coefficient was correlated with the decrease in air permeability.