Ebony bridge caps

[Michael Spreeman]

Hi David,
 
I'm not sure if your post was directed to me, but it's tagged onto a closing statement I made in a previous posting. In any event, thanks so much for your input, you provide substantial, reasonable, and clear data for consideration!  I'd like to attempt to comment on what you've brought to the table, but want to make it clear that I am no authority in this area, nor am I challenging your position; I'd like, rather, to offer some points to balance this ongoing discussion of bridge capping material.   Hopefully the readers aren't getting bored with our discussions. 
                Michael C. Spreeman http://www.spreemanpianoinnovations.com




> From: davidlovepianos at comcast.net> To: pianotech at ptg.org> Subject: RE: Ebony bridge caps> Date: Thu, 7 Jun 2007 09:53:13 -0700> > There are a few problems I have with the theory of harder bridge cap> material influencing the sound as described. First, the boxwood caps in> question are on average maybe 5-6 mm thick over a bridge that is 25 - 30 mm> thick. That bridge material is made primarily of maple and other woods that> aren't as hard, laminated or solid as the case may be. Even if the harder> boxwood cap transmits the higher partials (I assume that is what is meant by> brighter) more efficiently without filtering them, those frequencies still> must traverse another 80 - 85% of bridge body where there would be ample> opportunity for catching up on the filtering. 
 
I don't get the impression that anyone is implying that bridge cap material is the sole determining factor of harnessing and transmitting the energy of the strings into the soundboard. I am only suggesting that it is one factor that can be considered and altered in the overall assembly. I'm not a scientist, but when presented a scenario, I like to see what happens when a proposed idea is taken to the extreme.  If capping material is not important, then a sponge would be as efficient as titanium.  Without question, the bridge pin is held securly in place with the material in which it is placed. So, again I ask, why not use steel if the bridge pin is the only thing carrying the energy into the bridge body?  The bridge pin would be practically immobile, the surface wouldn't indent under pressure, and there would be minimal expansion and contraction with changes of RH.  I know that aluminum has been machined into bridge caps for experimental purposes, and it sounded horrible. So now we enter the arena of impedance.   
 
 
 Second, the point of contact> for the termination is really the bridge pin (marginally) which is both> harder and denser than either material and extends through the cap into the> bridge body which, since it is not made of boxwood, would still have the> opportunity to filter out those higher frequencies. 
 
If the bridge pin is the point of contact, then why not have the bridge pins go directly into the soundboard? Isn't there some interface between the bridge pin, bridge top, and string? If one were to place a thin piece of rubber between the top of the bridge and the bottom of the string, are you suggesting that the rubber would not absorb any of the energy from the string and the bridge pin would transmit this energy into the bridge regardless? Would the neighboring notes without the rubber sound the same as the one with?  I think I look at the bridge pin, bridge cap, and string interface as all being factors in "minimizing the losses".  It's all important and works together.
 
 
Third, the piano world> is replete with solid bridge bodies of maple and a variety of caps made with> other than boxwood that don’t seem at all compromised in this way. 
 
I'm not certain in "which way" you mean that they don't seem copromised, but I'd like to make a general observation about bridges here.  I have only my limited experience to share, and what I've been told by others about this subject.  I have 3 identical pianos (same size, same scale, same board thickness, same ribbing, same bracing, same rim structure, same belly rail, same type of hammers, etc.) with 3 different types of bridges.  One has a solid maple bridge, no cap, one has a vertically laminated body of maple and mahogany with hardwood caps, and one has a vertically laminated body of maple, ebony, and mahogany with hardwood caps.  I understand that the characteristics of the wood of the board, ribs, differnces in hammers even with the same manufacturer and same model,, etc.  However, the difference in sound between these pianos is gargantuous, far exceeding any differences caused by the differences of the boards or hammers.  The solid bridge is the least efficient.  Nice warm sound, ok duration, but no power.  The 2nd has around 30% more of both, and the 3rd yet another 30%.  Apparently something is going on between the string and the soundboard which is causing a marked difference in the sound of the pianos.  I'm thinking it's the bridges. 
 
Back to your bridge pin/termination point:  yes,, how very important it is.  Perhaps we should focus a bit on the bridge pin material,, hmmmmmmm????? > > The filtering of those high partials seems more likely a function of> inadequate stiffness in the board through the treble region and the board's> inability to reproduce the high frequencies transmitted through the bridge,> or, a function of inadequate mass in the rim and/or belly rail facilitating> unwanted bleed. 
 
I'm not real clear on what you mean when you say "filtering", but yes, once again: "minimize the losses" in every possible manner. And may I again, for the sake of those still awake, take the inadequate stiffness in the board theory to the extreme and suggest that it is important to not have the board too stiff.  It still needs to move, and I've seen "redesigned" boards with added ribs, thickened ribs, etc., in the treble where the result was disastrous.  The board was stiffened so much that there was almost no duration in the treble.  Like the bridge capping material discussion, there is an impedance point which cannot be so high as to cause problems.  At the same time, there is a workable tolerance that can be manipulated to produce the type of sound one is after.   
 
Whether or not some makers believed they could compensate> for killer octave problems with harder materials on the cap, I don't know.> I certainly do see the benefit of harder and denser wood on the cap to> resist compression damage from the strings over time and an eventual> compromise of the terminations. If I am incorrect, which is entirely> possible, I would love to hear the explanation.
 
 
 
 
> > David Love> davidlovepianos at comcast.net> www.davidlovepianos.com > > > > Having said all of that, (I also love dichotomies),I think most would agree> that throughout the conversations of boards, bridges, caps, etc, one theme> remains constant:  minimize the losses.  Lost energy is lost energy.> > Michael C. Spreeman > > > 
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