Soundboard stiffness variances

[John Delacour]

At 10:11 +0100 12/2/08, Richard Brekne wrote:

>...as for the variance of wood strength properties (in any 
>direction) with changes in humidity.  This is all pretty well 
>published and plastered all over the worlds various wood engineering 
>/ forestry department / etc websites...
>
>>"The strength of wood increases as the wood gets drier...maximum 
>>crushing strength in compression parallel to the grain and fiber 
>>stress at proportional limit in compresssion perpendicular to the 
>>grain is approximately tripled in drying from green to oven dry. 
>>Modus of Rupture (MR) is more then doubled in the process, but the 
>>stiffness is increased by only about half."

FIne.  I don't doubt it.  Green to oven dry is a long long journey 
and nothing in the working piano gets anywhere near either end of it. 
What we are concerned with is a comparatively small variation in 
moisture content, and if in completing that whole journey the 
"stiffness is increased by only about half" then I would guess, and 
can easily test it, that the differences in all these properties over 
the range we are dealing with are hardly significant.

I am all in favour of using the results of serious research to 
support arguments.  Things get shorter in the direction of travel as 
they approach the speed of light, and there is no such thing as a 
straight line, but in the range of our experience these facts are 
immaterial.

Let's test the properties of spruce over the range of dampness to 
which it will be subjected and then see how significant the change is.

JD