Sound absorption performance of wood: influence of porosity, gas permeability, and back air cavities in five wood species

Noise pollution is a growing concern in urban environments, driving the need for sustainable and effective acoustic materials. Wood, a naturally abundant and lingocellulosic material, exhibits sound absorption properties influenced by its porosity, gas permeability, and structural integrity. This study aimed to investigate the relationship between these properties and the sound absorption coefficient (SAC) of five wood types: Coconut (Cocos nucifera L.), Hackberry (Carya ovata), Malas (Homalium foetidum Roxb.), Oak (Quercus mongolica Fisch.), and Paulownia (Paulownia tomentosa). Using the two-microphone transfer function method, SAC was measured across a frequency range of 250–4000 Hz, both with and without back air cavities (0–4 cm). Additional analyses included porosity determination via helium pycnometer, gas permeability using a capillary flow porometer, and surface morphology assessment with a 3D optical profilometer. Results showed that back air cavities significantly enhanced low-frequency SAC. Hackberry and Oak achieved the highest Noise Reduction Coefficients (NRC) values (0.55 and 0.53, respectively at a 4 cm cavity depth). Porosity was critical for low-frequency absorption in Coconut (80.91%) and Paulownia (55.56%), while high permeability and large pore sizes favored low-frequency performance in Oak and Hackberry. Malas demonstrated balanced acoustic properties across frequencies due to its intermediate porosity and diffuse pore structure. This research highlights the novelty of correlating wood anatomy with acoustic behavior and optimizing back air cavity depth to tailor performance. The findings provide valuable insights for developing eco-friendly, wood-based acoustic materials for applications in construction, interior design, and noise mitigation solutions.