[pianotech] Increasing bridge height

[Will Truitt]

Hi JD:

Well, I agree with you that there can often be an irrational exuberance for
a Steinway.  Still, they can be awfully nice pianos, and it is what is
before me in my shop as my next project.

I make no claim to have any practical experience in deliberately modifying
bridge height, at least not yet.  But I am aware of the experience of others
in doing so, and have long thought about the relationship of bridge height,
stiffness, and mass.  My query here is to avail myself of the experience and
knowledge of others before making deliberate and calculated changes in this
piano.  

Others can tell you if the addition of 4 or 5 mm. along the length of the
bridge effects a meaningful change in the tone in areas other than the
treble.  But, to my ear, that is the area in Steinways that would most
benefit from this change.  I have long thought Steinways to be lacking in
volume and sustain in the treble compared to many other high quality
instruments. This is the area of the scale that would likely most benefit
from higher bridge stiffness and mass, yet the bridge is shorter and
correspondingly less stiff.  And the addition of the same amount of bridge
thickness will effect a larger percentage of change in the treble compared
to lower down in the scale.

I have wondered about lowering the inner rim in the grand scheme of things,
but have given it no consideration for reasons of practicality.

Sohmer added to the effective bridge height in the manner you describe for
the Grotrian, at least in their Cupid model, which also had the agraffe
bridge.  Your comment here is meaningful, because adding stiffness and mass
by having an "underbridge" would carry the virtue of not having to disturb
existing relationships between the action and the string plane, unless there
were other compelling reasons to do so.   

If the only changes that need to be made in the action to accommodate
changes in bridge height on the topside bridge are the hammer bore distance,
and there are no other attendant penalties; then it would remain the
simplest possible way to effect the desired change. Other than the necessary
calculations, you are not really adding much work.  You have to cap the
bridge anyway, you have to thickness the pinblock anyway, and you have to
bore the hammers anyhow, and you have to set plate height at the rim.  So I
remain most attracted to this methodology.

Thank you for your (as always) insightful comments.

Will 

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of John Delacour
Sent: Tuesday, March 24, 2009 3:46 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Increasing bridge height

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