Vibrational properties of wood along the grain

The dynamic Young's modulus (E'(L)) and loss tangent (tan delta(L)) along the grain, dynamic shear modulus (G'(L)) and loss tangent (tan delta(S)) in the vertical section, and density (rho) of a hundred spruce wood specimens used for the soundboards of musical instruments were determined. The relative acoustic conversion efficiency (alpha, root E'(L)/rho/tan delta(L)) and a ratio reflecting the anisotropy of wood (beta, (E'(L)/G'(L)) (tan delta(S)/tan delta(L))) were defined in order to evaluate the acoustic quality of wood along the grain. There was a positive correlation between alpha and beta, and the variation in beta was larger than that in alpha. It seemed logical to evaluate the acoustic quality of spruce wood by a measure of beta. By using a cell wall model, those acoustic factors were expressed with the physical properties of the cell wall constituents. This model predicted that the essential requirement for an excellent soundboard is smaller fibril angle of the cell wall, which yields higher alpha and higher beta. On the other hand, the effects of chemical treatments on the alpha and beta of wood were clarified experimentally and analyzed theoretically. It was suggested that the alpha and beta of wood cannot be improved at the same time by chemical treatment. (C) 2000 Kluwer Academic Publishers.