The influence mechanism of tung oil and paraffin oil heat modification on the acoustic vibration characteristics of Jinghu soundboxes

Bamboo is widely used in traditional musical instruments because of its unique vibration characteristics, yet its moisture sensitivity leads to variations in structural and acoustic responses during service. However, how chemical modification regulates the multiscale structure and vibration behavior of bamboo soundboxes remains poorly understood. Here, we investigate the effects of tung-oil and paraffin-oil heat treatments on the structural evolution and acoustic performance of Jinghu bamboo soundboxes by integrating chemical, crystallographic, three-dimensional pore, and vibration analyses. We show that the two modifiers regulate acoustic behavior through distinct structural pathways. Tung-oil treatment primarily alters the cell-wall interface and pore environment through penetration, resulting in modified damping characteristics and vibration responses. In Erhuang bamboo soundboxes, the RMS amplitude increased from 1.15 Pa to 1.67 Pa, accompanied by a 45-60% reduction in damping ratio. In contrast, paraffin-oil treatment induces pore filling and spatial redistribution of the internal pore architecture, increasing cellulose crystallinity from 23.4% to 37.1%, reducing total porosity from 40.70% to 28.34%, and increasing the calculated permeability coefficient to 108.82 μm². These structural modifications regulate stiffness, energy dissipation, and vibration transmission pathways, leading to distinct modal responses between the two treatments. Our findings establish a structure–property–acoustic framework for understanding oil-based modification of bamboo soundboxes and provide a mechanistic basis for designing functional bamboo materials with tunable vibration characteristics.