Soundboard mass

[David Love]

In view of this it is interesting that one almost always finds bridges on
older Steinways that diminish in height through the capo sections.  The
bridge in question was on the order of 27 mm through the treble and I've
certainly seen them drop well below that by the time they get to C88.  While
I understand the effect of an increase in height of the bridge on overall
stiffness, I suppose I'm wondering whether a better protocol for working
with older and tired soundboards that aren't quite ready for the scrap heap
might not be to simply recap the bridge complete adding, in similar cases,
7-8 mm.  One may need to add some thickness to the new pinblock and raise
the plate a bit and, of course, it would change the hammer bore, but I'm
trying to think of a downside.  Even in the case of the dampers, I'm often
replacing the old underlevers with a new Renner one where the wires often
need to be trimmed.  In this case the extra length would be welcomed.  Any
thoughts on the downside of this, if any?

David Love
davidlovepianos at comcast.net 
www.davidlovepianos.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of John Delacour
Sent: Saturday, November 24, 2007 1:56 AM
To: Pianotech List
Subject: Re: Soundboard mass

At 18:51 -0600 21/11/07, Ron Nossaman wrote:

>[At 16:04 -0800 21/11/07, David Love wrote:]
>
>>Anyway, I'm wondering if others have done similar things with similar
>>outcomes or found that bridges below a certain height simply don't have
>>enough mass without some help.  Further, with a certain minimum bridge
>>height does mass loading become unnecessary?
>
>I think it's stiffness, rather than mass that makes the most 
>difference in the taller treble bridge...

I think so too.

Writing in 1916, Wolfenden says :

         "For very many years both long and bass bridges were cut out
         of 1 in. [25mm] beech, and were often finished under
         7/8 in. [22mm] in height, but of late the long bridge,
         by general tacit consent, stands 1-15/16 in. [33mm] to
         1-1/2 in. [38mm] above the belly and the bass bridge from
         3/4 in. to over 7/8 in. higher still.
           No definite proportion between the tension of the strings
         and the height of the bridge has been discovered.  It would
         not be surprising were it to be found that a further increase
         in height was of advantage."

The stiffness of the bridge increases as the _square_ of the height, 
to that a bridge of 33mm is about 70% stiffer than one of 1 inch and 
a bridge of 38mm is 33% stiffer than one of 33mm.

Of the pianos I have in the shop at the moment, neglecting those with 
a double bridge, most have bridge heights closer to 33mm but two Lipp 
uprights (which I consider the best upright ever made) have a 
38mm-40mm bridge and so do two 6'9" Kirkmans from about 1865, which 
also have a wonderful sound.  One day I plan to analyse the sound 
scientifically but I have the impression that what characterises the 
pianos with the tall bridge is that the tone is almost fully 
developed and pure at the attack, the decay very smooth and the 
sustain exceptional.  They also allow, or should I say require, the 
use of a very firm hammer, without which only a fraction of their 
wonderful potential is available.

JD