Tonewood grains per inch

[thepianostore]

Great, I can see it now.  "Young Chang Lite--'Sounds Great, Less Filling'"

-----Original Message-----
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On
Behalf Of Phillip Ford
Sent: Thursday, November 14, 2002 7:13 PM
To: pianotech@ptg.org
Subject: Tonewood grains per inch


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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