Investigation into sound absorption properties of 3D cone knitted structures and their composites

Abstract

Noise pollution has become a global issue which adversely affects human health. Therefore, noise should be controlled for the comfort of humans. Textiles are widely recognized as cost effective and environmentally friendly solutions for sound absorption. Among textiles, three-dimensional (3D) knitted cone structures which have higher surface area and fiber content than normal fabric can be ideal for sound absorption. The acoustic behaviour of 3D knitted cone structures was mathematically investigated by developing a mathematical model using basic equations of fluid dynamics. The samples were produced with variations in loop length, cone geometry and structural characteristics to investigate their acoustic properties experimentally using reverberation room method. A reverberation room was developed with a volume of 2.06 m³ and an asymmetric design, overcoming limitations of conventional test methods. The test results demonstrated that shorter stitch lengths enhance sound absorption properties at higher frequencies (f > 1000 Hz) whereas, at low frequencies, the effect of the stitch length on sound absorption was negligible. Furthermore, cone geometry significantly influenced the acoustic behaviour of the knitted samples. Samples with taller and narrower cones led to greater sound absorption at low frequencies (f  1000 Hz) while wider and shorter cones demonstrated better absorption at middle and high frequencies. It was further observed that, through the parametric comparison of samples based on the physical parameters such as density and air flow resistance of cone knitted structures, sound absorption coefficients close to 1 can be obtained above 2500 Hz frequencies. The experimental results closely matched the model predictions with a root mean square error (RMSE) of 0.02982 and a mean absolute error (MAE) of 0.02410, confirming the accuracy of the developed mathematical model. Geometrically stable cone knitted samples without compromising acoustic performance were obtained by applying a thin layer of epoxy resin which are suitable for use as acoustic absorbers. The results confirm that cone knitted structures provide a sustainable solution for sound absorption in building applications