Edwin R. Fitzgerald
Johns Hopkins Univ., 3400 N. Charles St., Baltimore, MD 21218
Carleen M. Hutchins
Morton A. Hutchins
Catgut Acoust. Soc., Montclair, NJ 07042
Values of complex shear compliance (J*=J'-iJ''), modulus, (G*=1/J*), and shear sound velocity and attenuation have been measured over a continuous frequency range from 10 to 10 000 Hz for samples of spruce and maple wood used in the construction of six violins. Measurements were made with an automated electromagnetic transducer system in which samples are sheared while clamped between stainless steel blocks. [E. R. Fitzgerald, Proc. Am. Chem. Soc. Div. Polymeric Mater. Sci. 60, 573--578 (1989); E. R. Fitzgerald, U.S. Patent 5,081,870 (1992)]. Four wood samples were measured for each finished violin, viz., samples of spruce and maple with and cross grain. As reported earlier, values of the shear parameters vary with frequency and grain orientation, but also with moisture content and the clamping force on the sample faces while they are vibrated in shear [E. R. Fitzgerald, J. Acoust. Soc. Am. 89, 1927(A) (1991)]. The details of the mechanical spectra of the six sets of samples vary, but, in general, several sharp, microstructural compliance modes are superimposed on broad retardation spectra [E. R. Fitzgerald, J. Acoust. Soc. Am. 33, 1305--1314 (1961)]. Comparisons among the six sample sets are made for the same clamping force at 20 (degrees)C and 52% R.H.