Ebony bridge caps

[Michael Spreeman]

                Michael C. Spreeman http://www.spreemanpianoinnovations.com




> From: jimialeggio5 at comcast.net> To: pianotech at ptg.org> Subject: Ebony bridge caps> Date: Mon, 11 Jun 2007 12:37:40 +0000> > Michael, Ron, etal,> > I've been following this thread with interest, and thinking about some of the > concepts.
 
Me too!  This has been VERY thought provoking for me, especially considering the exerience and quality level of those who are contributing.> > One piece of the explanations for the observed effect of the multi-species > laminations doesn't make sense to me, and I wanted to run it by you all.> > Regarding Michael's experiment, ie, three identical pianos with three different > bridges, 1-solid maple,2-maple with mahogany laminations, and 3-maple with > mahogany and ebony laminations... > > The explanations for the observed effects all seem to point to the effect of > increased density/mass.> > Here's my question. In the 2nd piano example, maple and mahogany laminations: > since the specific gravity of mahogany (swietenia macrophylla= .51) is actually > less than that of maple (.63), this bridge is actually less dense than the stand > alone maple, assuming absolute density is what we are looking at.
 
The specific gravity of the wood is higher in the maple, or at lease we are assuming that this "specific piece" of maple has a higher specific gravity than the maple/mah, but the overall weight of the mah/maple laminated bridge is more; there has to be a reason for this.  After thinking about Ron's question about weight, I weighed the 3.  The solid maple comes in at 3.5 lbs, the mah/maple 4.0, and the ebony/mah/maple at 4.5.  Don't ask me why!  Maybe Terry used lead based epoxy in the maple/mahogany laminated bridge :) The maple/mah laminated bridge may have maple which is a higher specific gravity than the maple of the solid bridge.  The solid bridge looks to have much wider grain than the beatufiul maple Terry used in the laminated bridge.  I don't know what the mahagony in the laminated bridge is, Terry was the head chef on that.> > To my mind, this doesn't jive with the straight-up absolute density > explanations...unless... the effect of increased density occurs as much from the > layers of non-uniform densities introduced by layering different species (with > differing densities), as from the > actual absolute densities of the woods. 
 
There's MUCH more I don't know about this than what I do know.  Part of the intruige for me in this thread has been the subject of mass loading which has been touched on.  Between that and Ron's comment about the "magic vibrations theory", it is challenging most of what I thought I understood about what's "really going on in that there belly". My initial thinking is that a vertically laminated bridge is more efficient than a solid bridge.  But there's no question that the mass has to play into this.  Back to the extremes, I seriously doubt that a laminated bridge made with balsa could compete with a solid maple bridge.  
 
> > Does this make any sense?> > Jim I> > 
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