Ebony bridge caps

[Michael Spreeman]

Nice one.  I'll keep that in mind 8-).
 
                Michael C. Spreeman http://www.spreemanpianoinnovations.com


From: mfarrel2 at tampabay.rr.comTo: pianotech at ptg.orgSubject: Re: Ebony bridge capsDate: Mon, 11 Jun 2007 17:14:17 -0400



> 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.
If the volumes of the three samples is the same, I see no good reason that the solid maple would be lighter than the mahogany/maple sample. It is obvious from handling the wood that the mahogany is much less dense than the hard maple. Obviously, your statement: "The maple/mah laminated bridge may have maple which is a higher specific gravity than the maple of the solid bridge." is true, but why? Can I assume the solid maple sample did not originate from my shop? Is there any chance the solid maple sample is soft maple? That's about the only explanation I can think of.
 
It doesn't surprise me that the mahogany/maple/ebony assembly is more dense than the other two - that ebony is extremely dense - small pieces of it weigh a bundle. I used a two-part urea-formaldehyde resin adhesive for both the mahogany/maple bridges and the mahogany/maple/ebony bridges.
> 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.  
 
I think that could be applicable if you believe that sound propagation along the length of the bridge has a significant influence on sound ultimately eminating from the soundboard. If one subscribes to the theory of strings vibrating the bridge, which vibrates the soundboard, which moves air, then perhaps there is not likely not much difference between a solid and laminated bridge. The biggest reason I like a laminated bridge root is because it should never crack.
 
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.   As you state, you would have mass issues with a balsa bridge root. But you might find the balsa is so soft that it imparts a damping effect between string vibration and soundboard movement. Might not want to spend too much time experimenting with balsa. 
 
However, if you are a paying customer and want me to build you one........  ;-)
 
Terry Farrell
> Does this make any sense?> > Jim I> > 



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