Sound board trenching and stuff

[Ric Brekne]

Ron O writes:

As someone responded to Dean's suggestion, we've been trenching
boards for many years now (since about the mid 90's). Seiler have
been trenching the entire sound board perimeter for even longer.
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Just got back from the NPTA convention in Stocholm where this exact 
subject matter was discussed by Joachim Leonardy from Seiler in his 
lecture. Unless I totally mistunderstood it was his position that the 
reasons for doing this exact proceedure were based on an assumption that 
the wood in the soundboard that lies above a line of force that exists 
from the highest point of the soundboard to the underside of the panel 
where it joins to the rim along any given axis is really unneccesary 
from a structural support perspective.  This was at least part of why 
Steinway and Sons came up with their tapered soundboard.  Seiler would 
do the same thing except the proceedure is very expensive, so they 
decided to come up with an alternative method of accomplishing more or 
less the same thing.  As I read his comments, this was a way of cutting 
costs quite a bit at an exceptable reduction in the effectiveness of the 
scheme comparied to the S&S method.

Btw... Joachims lecture was one of the best I've ever heard on the 
general subject matter of soundboard function and construction... in the 
sense that it wasnt flooded with a lot of math and physics concepts that 
go over the heads of 90 % of the audience. Tho it was extremely 
understandable for the layman average tech on the beat, it was still 
very well explained, clear, and left nearly everyone there with a much 
better understanding of soundboard function as he views it.  Also, for 
what its worth. Seiler subscribes to the idea that the highest possible 
stress levels need to be achieved in the assembly for the best possible 
and most enduring tone. Seiler takes particular pains to create as much 
along the grain compression in their soundboards, and use every device 
to obtain as much compression in both directions as possible, including 
installing the assembly while very dry to a very tight fit to the rim so 
that upon taking on humidity end grain support of crown is also in the 
picture.  They also tension the bridge on attachment to the soundboard.

Of other interest... Petrof tapers their soundboard planks before 
glueing them together so that  there is a slightly increasing gap 
between planks towards the middle of two adjacent planks.  Their 
research shows  that this proceedure increases the stiffness to mass 
ratio significantly as I understood Jan Scalas lecture. They also have 
been doing this for several decades... from before there was any kind of 
scientific method applied to see if there was any real benifit to doing 
so.  Where they got the idea in the first place I am sure I dont know.

Cheers
RicB