Influence of Perforation Geometry and Lamination on the Acoustic Properties of Natural Fiber Composites

Abstract The growing demand for environmentally sustainable building materials has increased interest in natural fibre–reinforced polymer composites as alternatives to conventional synthetic interior cladding systems. In this study, composite wall panels fabricated from hemp and sheep wool fibres embedded in an epoxy matrix were investigated to evaluate the influence of laminate configuration and perforation geometry on acoustic performance. Three laminate architectures Hemp/Wool/Hemp (H + W+H), Hemp/Hemp/Hemp (H + H+H), and Hemp/Wool/Hemp/Wool (H + W+H + W) were initially assessed for mechanical performance, and the H + W+H configuration was selected as the benchmark laminate for acoustic optimization based on its balanced flexural and functional characteristics. A total of forty perforated panel configurations were fabricated by varying perforation diameters (2.5–4.5 mm) and the number of stacked layers, with all samples tested in a reverberation chamber in accordance with ISO 354. Acoustic performance was evaluated in terms of Sound Attenuation Level (SAL) across the frequency range of 125–4000 Hz. The results demonstrate that multilayered panels incorporating smaller perforation diameters exhibit enhanced mid-frequency attenuation (500–2000 Hz), which is particularly relevant for indoor acoustic applications. The maximum attenuation of 48.8 dB at 2000 Hz was achieved for the 2.5 mm + 3 + P configuration, while several other multilayer combinations exceeded 46 dB. The findings highlight the strong dependence of acoustic performance on perforation geometry and laminate stacking sequence, confirming the potential of hemp–wool hybrid composites as sustainable acoustic panel materials for interior architectural applications.