Soundboard mass

[Ron Nossaman]

> Indeed! I was not making the distinction between strength and resistance 
> to flexure, ie. stiffness, presuming erroneously that they were the 
> same, so it can be said that "the strength of a rectangular beam varies 
> as the square of the depth, and the stiffness to resist deflection 
> varies as the cube of the depth" as you say, which means that a 38mm 
> bridge is more than 50% stiffer than one 33mm tall and if one were to 
> increase the height to 40mm. there would be a 78% stiffness advantage.

If you're talking about loading to failure, it's a moot point 
in a bridge, since the flexural loads aren't anywhere near the 
limit of strength. Stiffness is exactly the quality in question.


>>  A similar net effect can be gotten with a short bridge with the 
>> addition of more crowned ribs.
> 
> That I am not qualified to calculate, but I am thinking of the whole 
> length of the bridge and perhaps you are thinking more of remedial 
> measures for weakness in a troublesome part of the scale as found 
> commonly in old American Steinways (the "killer octave" ??).  To stiffen 
> the whole stucture by this means would surely mean adding quite a lot of 
> unwanted mass, many times more than by increasing the bridge height or 
> adding a "mirror bridge" as used by Grotrian, Rittmüller et al.    To my 
> mind a high ratio of stiffness to mass is of prime importance.
> 
> JD

I'm talking about in general, a lesser bridge height can be 
effectively compensated for by increasing the number of load 
supporting ribs. If these ribs are shortened through the 
treble with cutoffs, considerable stiffness can be obtained 
with a net reduction in mass, if that's what you want. Ribs 
can also be reconfigured to be deeper and narrower, again 
increasing stiffness without being locked into any particular 
mass as a result. They can also be made wider if you want more 
mass. The whole point of redesign with rib crowned and 
supported boards is that you get to make these decisions 
consciously and deliberately rather than taking what the 150 
year old approaches and assumptions leave you stuck with. This 
isn't smoke and mirrors. A number of small shop rebuilders are 
currently doing this stuff quite successfully.
Ron N