Optimizing acoustic vibration performance in Sitka spruce via grain inhomogeneity analysis: A hybrid approach of image processing and vibro-acoustic characterization

The inhomogeneity of the cross-sectional grain of Sitka spruce wood was analyzed using image processing techniques, and the influencing mechanism of this inhomogeneity on the acoustic vibration properties of the wood was investigated. The inhomogeneity of grain width was characterized by the average deviation of the growth ring width and latewood rate of the test specimens. The inhomogeneity of grain position distribution was characterized by the average deviation of the variation in growth ring width. The influence of the inhomogeneity of these grains on the acoustic vibration properties of the wood was investigated respectively. The results showed that as the inhomogeneity of the growth ring width and the growth ring width variation increase, the values of the specific modulus of elasticity (E/ρ), acoustic radiation quality constant (R), and acoustic impedance (ω) of the wood decrease, while the value of the loss angle tangent (tan δ) increases. As the inhomogeneity of the latewood rate increases, the values of E/ρ and R of the wood decrease, and the value of tan δ increases. The inhomogeneity of the latewood rate has no significant effect on ω. When the width of growth rings was between 0.14 cm and 0.17 cm while the deviation of the growth ring width ranged from 0.024 to 0.036 and the deviation of the width variation ranged from 0.016 to 0.020, the wood had relatively large values of E/ρ and R and a relatively small tan δ value, leading to better acoustic vibration performance. Similarly, when the latewood rate was between 15% and 20% and the deviation of the latewood rate ranged from 0.030 to 0.045, the wood had relatively large values of E/ρ and R and a relatively small tan δ value, leading to better acoustic vibration performance. This result provides more reference data for the rational selection of materials for musical instruments.