Ebony bridge caps

[Michael Spreeman]

JD,
 
Yes, I agree with most of your detailed points and also agree with Dale that your post is pleasantly succinct.  There is also a manufacturer of uprights in UT, Astin Weight, who use the "simplest expedient to achieve a stiffer bridge" by using taller bridges.  The pianos I have heard with tall bridges have a "unique" sound.  It's not a "bad" sound, it's just not the sound I was after in this piano.  It would be interesting to experiment with this practical principle as well and perhaps I will have time in the future to do so.  At present, I am quite satisfied with the results of the shorter bridges with ebony.
  
I have to admit that the original theory for using the different woods for laminations, and the selection of materials for the cap had more to do with having varying densities of woods than it did with a focus for a stiffer bridge with more mass.  For me, the stiffness and mass are characteristics that resulted from a decision to have a more efficient transducer than an original concept or decision to increase mass and stiffness.  A consideration for the soundboard thickness, rib dimensions, number of ribs, density and placement of ribs, radius of ribs, radius of press cauls, resulting crown, grain orientation, and attempting to create a bridge which would function most efficiently with this unit as a "whole", was primary. So, the type of bridge to be used was the first decision; completely solid, solid body with solid cap, vertically laminated, vertically laminated body with solid cap, vertically laminated body with horizontally laminated cap, horizontally laminated body with solid cap,, and on and on. All have their merits and shortcomings. Next, what materials to be used in the bridge was considered, then the dimensions, with an understanding that in the end all these things together would effect mass and stiffness.  Having plowed through the numerous threads and input on this subject, it could appear that I am way off base and have taken an incorrect approach.  Maybe I did,,, I don't know.  If I were to start all over again from the beginning, I can't say that my approach would be too much different.  Some would consider it a good approach,  and some an erroneous one, thus is life.  I suppose one could design a board around a bridge as opposed to a bridge to compliment a board, or any other number of approaches, but in the end they must play nicely in the sand box together. 
 
Like most of us, ultimately my focus was on creating a musical instrument, not just a well engineered structure like the Golden Gate bridge, or a sky scraper.  Yes, the musical instrument must be structurally sound and designed in order to insure longevity and this comment is NOT to imply that the discussions in this thread have been restricted only to matters of physics and mathematics, but rather which principles and materials combined would result in a specific sound profile.  These principles are imperative considerations.  Most of the input has been based on experiential knowledge and application, but some of it involves speculation.  Both the speculation aspects and the sheer facts lend an interesting, thought provoking format for discussion and have been very eye opening and enjoyable to be a part of. There is a type of musical, piano sound profile I was after in this one piano which is subjective, and for whatever reasons, be it logic, science, analysis, magic fairy dust, or sheer luck, I attained the results I was after, so, by all means, let's analyze and decipher the specific "whys" of how it works.   Whether the ebony cost was horrific , a pure waste of money, or not even necessary was not a primary consideration. It, to me anyway,  was a necessary means to an end to produce a specific result I wanted.  And no, in my opinion,  it did not create a detrimental result in the tenor, just the opposite.  The tenor has a wonderful clarity with a broad dynamic offering and the transition at the break is quite even as a result this (and a few other considerations). The additional expense was well worth the benefit.  Discuss, analyze, and  even criticize if this gives you pleasure, but please attempt to refrain from pre-judging and guessing whether one's decisions to invest in more expensive materials is horrific or a pure waste until you've personally felt and heard a piano with this specifc type of construction. 
                Michael C. Spreeman http://www.spreemanpianoinnovations.com


From: Erwinspiano at aol.comDate: Tue, 12 Jun 2007 18:39:24 -0400Subject: Re: Ebony bridge capsTo: pianotech at ptg.org

  Jd
  Nice clear post. Especially the underlined. Comments below
  
It seems to me that a laminated hardwood bridge is not only stiffer but will, stiffness aside, transmit the vibrations more quickly and efficiently by dint of the direction of the grain.  Add to that the virtues of ebony or a dense rosewood (dalbergia xxx) and you have almost certainly a "faster" bridge.  What surprises me is that so few makers have used the simplest expedient to achieve a stiffer bridge, and that is to make it taller, since the stiffness increases as the square of the height, so that a 38mm bridge will be twice as stiff as a 27mm bridge of similar construction and a great deal stiffer than a 27mm bridge using ebony laminations without the horrific cost.
  I have a 6 ft Julius Bauer that has a very tall bridge.ie roughly 37mm  The belly system is VERY  stiff in spite of the lack of rib support
I'd say the question of mass is very low in importance compared with questions of stiffness and speed of sound in the bridge.  The bridge is a transmitter and also a filter.  The capping of the bridge in the top treble with a suitable hard and dense wood reduces the filtering, which needs to be different in different parts of the scale according to the quality of sound one aims to achieve. 
  I especially like this above. I'm not sure I've ever heard it explained that succinctly.  Or... maybe I wasn't listening.
  Cheers
  Dale
The use of ebony at all in the tenor and the bass would strike me as a pure waste of money and likely also to have tonal effects that might not be desirable.JD

 


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