Aging mechanism of the acoustic vibration characteristics of Jinghu sound boxes with different preservation ages

To elucidate the material science principles underlying the empirical belief that aged bamboo yields superior acoustics, this study investigates aging-induced changes in the acoustic performance of Jinghu, a traditional Chinese bowed-string instrument, using bamboo soundboxes subjected to three natural aging durations: 86 years (XP-86), 46 years (XP-46), and 3 years (XP-3). A multi-scale approach that spans macro-to-micro dimensions and structural-to-compositional perspectives was employed to characterize vibrational efficiency and timber quality. Long-term natural aging effectively minimizes internal interfacial energy dissipation. XP-86 exhibited the optimal synergy between stiffness and damping, achieving superior vibration transmission and tonal depth. Compared with XP-3, XP-86 exhibited a higher natural frequency (2417.50 Hz) and dynamic modulus of elasticity (9.70 GPa), while maintaining lower damping, a smoother frequency response, and more uniform modal distribution. Therefore, XP-86 showed the best overall stiffness–damping balance rather than the maximum value for every individual parameter. These enhancements stem from structural-compositional co-evolution. Specifically, the microfibril angle (MFA) decreased from 6.51° to 6.18°, optimizing the conductive framework. Degradation of starch granules reduced non-elastic friction loss. At the chemical level, hemicellulose degradation and lignin condensation and densification, as indicated by decreases in β-O-4 linkages and the syringyl-to-guaiacyl ratio (S/G ratio), enhanced cell-wall rigidity and structural stability. This study provides a rigorous theoretical foundation for the empirical ripening of bamboo, linking microscopic molecular reorganization to macroscopic acoustic excellence.