Ebony bridge caps

[John Delacour]

At 9:45 am -0600 11/6/07, Michael Spreeman wrote:

>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",Êit isÊchallenging 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.

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'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.  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