This just in. The latest issue of The Catgut Acoustical Society Journal reports that according to researchers at the University of Padova in Italy, and here I quote from their abstract, 'No evidence was found of a relationship between physical and acoustical properties (density, modulus of elasticity, index of merit) and external aspects of Italian red spruce (mainly growth ring distance).' Further excerpts from the paper - direct excerpts are in quotes, other words are mine: 'According to many studies (see Reference 1 at end of post - PF), frequency response and acoustic efficiency .. are mostly influenced by the following parameters: 1. Density 2. Modulii of elasticity El and Er.' El is longitudinal modulus of elasticity Er is radial modulus of elasticity 'Twenty-one planks of Italian red spruce, originally cut for piano soundboards, were taken from Fazioli and Ciresa stock.' 'All the planks were seasoned for more than 2 years before being cut into 300 specimens.' The researchers attempted to correlate growth ring distance (grains per inch) and percentage of late growth of rings, to density, moduli, and index of merit. Note here that index of merit is given by (from reference 1 at end of post): M = [(El x Er) ^ 1/4] / d ^ 2/3 Since this equation doesn't come across so well on e-mail let me express that in words: Index of merit is equal to the product of Logitudinal Modulus and Radial Modulus to the one-fourth power divided by density to the two-thirds power. According to reference 1 woods with higher values of M are more suitable for soundboards. The conclusion of the paper was: 'A functional relationship cannot be established between the spacing of growth rings and acoustic properties for 21 samples of red spruce from northern Italy. This suggests that optical regularity and dimensions of growth rings are unreliable indicators of physical properties.' The Index of Merit indicates to me that desirable properties for soundboard woods are high stiffness and low density (no real surprise there). However, since the moduli are to the 1/4 power and the density is to the 2/3 power that says to me that stiffness is nice, but lightness is nicer. But neither of these things can you reliably determine from looking at a piece of wood. Ref 1. Barlow, C Y , 1997, Materials selection for musical instruments: Proc. International Symposium on Musical Acoustics (ISMA 97), Edinburgh, Scotland, p 69 - 78.
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