[pianotech] Increasing bridge height

[John Delacour]

At 19:13 -0500 23/3/09, Will Truitt wrote:

>Well, JD, you certainly are a good salesman for the concept... ...

Maybe, but I'm not sure how much improvement you would effect in a 
Steinway by the modification you envisage except perhaps in the 
treble. Every few millimetres in total bridge height will make a 
little difference and, by simple mechanical laws, increase the 
stiffness by more than the proportion of the added height to the 
original, but you will not achieve a step change by so small an 
increase.

As Ron says, the string height in the Steinway is likely to be lower 
at note 88 than in the middle.  There's good reason for this in 
pianos with studs (agraffes), as I explained recently.  Why Steinway 
continued the practice, using the capo bar, heaven knows.

Raising the string height is not the only way to increase the 
effective bridge height.  One alternative is to lower the inner 
rim/soundboard, possibly necessitating cut-outs in the framing to 
allow the passage of the bars.  I've done this a couple of times with 
experimental models, and it's a lot of work without a good set-up.

A simpler way is to do what Grotrian, Rittmüller and others did and 
add to the bridge height from underneath.  I've never been impressed 
with the result Grotrian achieved with the double bridge, but I think 
that's because of their actual design rather than a fault in the 
principle.  This way you have a far simpler task and can increase the 
effective bridge height as much as you like without changing the 
string heights and getting all the bother that ensues from this.  If 
I were doing this, I would calculate (or get a better engineer to 
calculate!) what _width_ of under-bridge would be required for a 
given under-bridge depth (which must be 1/4" greater than the depth 
of the bars) to produce a structure that is as stiff as a simple 
45-50 mm over-bridge.  This would almost certainly result in an 
under-bridge narrower than the over-bridge.  I guess that Grotrian's 
'mistake', as I would call it, was to over-egg the pudding.  One day 
I must sit down and do the calcs.  Rittmüller, by the look of it, put 
more thought into the matter.

As a man with a very limited admiration for Steinway's supposed 
genius, I myself would start with a better piano!

JD