Ebony bridge caps

[David Love]

My comments were meant for the general discussion.  Comments inserted.

 

David Love
davidlovepianos at comcast.net
www.davidlovepianos.com 

 

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
<http://www.spreemanpianoinnovations.com/> 





 
 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.   

There are many reasons a sponge would not be as effective: not holding the
pin or string securely not the least of them.  I can't describe what happens
when you make a bridge out of aluminum that makes it sound horrible, but I'm
also not arguing for the need to go that hard.  I would think that a steel
bridge would impact soundboard movement-manufacturing might be a problem as
well.  


 
 
If the bridge pin is the point of contact, then why not have the bridge pins
go directly into the soundboard?

My point was that the bridge pin transmits some energy to the bridge body, I
don't think it's necessary for the pin to go into the soundboard for the
energy to get there via the bridge.  

 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.
 

The rubber might very well absorb some energy because of the flexible nature
of the material.  But we're not comparing boxwood and rubber, but boxwood
and hardened maple.  

 
 
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. 

Hard for me to comment on this:  you're saying that the 60% increase from #1
to #3 is the bridge?  I find that difficult to believe.  I've replaced
boxwood caps on pianos with hardened maple and have not recorded any drop
off in power or sustain. 


 
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????? 

 

Solid bridge termination is critical to control loss of energy, I agree.  A
firmly attached pin with adequate diameter is important, I think.  



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.   

 

Bridges and soundboards filter certain frequencies in certain areas.  A
killer octave (among other things) due to its lack of stiffness, filters out
high frequencies produced by the string.  The lack of stiffness also
compromises sustain.  Part of what you hear is the lack or weakness of upper
partials on those notes.  Recall, soundboards do not produce any partials on
their own, they can either effectively transduce the ones provided by the
string or filter them out due to their inability to reproduce them.
Certainly you can overdesign a soundboard.  Simply adding a rib or
thickening them is not the solution.  Creating an effective spring in that
section with balance between mass and stiffness in order to control the
point of balance along the continuum of power and sustain is the trick.  


 
 

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