[pianotech] Increasing bridge height

[John Delacour]

At 17:41 -0500 22/3/09, Will Truitt wrote:

>Hi JD:
>
>Thanks for your further comments on top of Del's.
>
>Many of the old Chickering grands had low bridges at heights in the range
>you describe, and not a particularly powerful or satisfying tone - they can
>sound a bit flabby to me.

Flabby is a good word, and I think that is just what it is, not only 
tonally but mechanically -- The bridge undulates.

>The why of the taller the bridge is what most intrigues me.  All else being
>equal, the taller bridge will have more mass.  I think we probably have a
>better understanding of the role of mass in the bridge than we do stiffness.

I think it is the stiffness that matters.

>...But that taller bridge is also going to be stiffer - how much 
>does that add to the improved performance of the soundboard?  How 
>much stiffness do we need to achieve optimal performance?

I'd say that the vibrations put into a stiff bridge will be better 
transmitted without loss to a greater proportion of the soundboard. 
A good piano with a tall bridge has qualities that are not met with 
in pianos with lower bridges, among which I'd list a very definite 
and pure attack and a good decay curve; good sustain; a wide spectrum 
of tone colour, and an indefinable correspondence between the voices, 
with the sustain pedal producing effects not possible with a low 
bridge.

>I recall reading in "Piano Tone Building" about experimental bass bridges
>which were made out of Vanadium instead of maple or beech.  These bridges
>were much stiffer than the wood ones, and had a dramatically longer sustain
>times - but not a pleasing tone.

That book of wonders contains more long-winded nonsense than most!

>Still, it points to the potential value that added stiffness might 
>have, particularly in this modern age of composite structures, where 
>various materials are combined to achieve a blend of properties.

Kirkman's tall bridges, on the grands at least, were built of spruce 
with a thick (about 1/2") beech capping and steep notches.  Sound 
travels faster in spruce.

JD