Soundboard mass

[John Delacour]

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