[pianotech] Increasing bridge height

[Will Truitt]

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.

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.
Our R,C, & S bellymen who regularly mass load bridges to targeted levels to
fine tune the performance of the soundboard can attest to the importance of
that from their own experience.  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 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.  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.

Will Truitt



-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of John Delacour
Sent: Sunday, March 22, 2009 4:18 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Increasing bridge height

At 15:21 -0700 21/3/09, Delwin D Fandrich wrote:

>I don't really like treble bridges that are 24 to 25 mm tall. I want 
>to end up with a bridge height of at least 30 mm at C-88.

I'd say that is very conservative.

In 1916, Wolfenden wrote:-
______________________________
"For many years, both long and bass bridges were cut out of 1 in. 
[25.4mm] beech, and were often finished under 7/8 in. [22.2mm] in 
height, but of late the long bridge, by general tacit consent, stands 
at 1-15/16 in. [33.3 mm] to 1-1/2 in. [38.1mm] 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."
______________________________

In fact one English maker had already been building uprights and 
grands with a bridge 42 - 44 mm in height for nearly 50 years before 
this was written, having changed from a 1" bridge as soon as the low 
tension pianos were discontinued in favour of the modern scaling with 
the new wire.  And these pianos are, without exception in my 
experience, powerful, clear and subtle with excellent sustain.

I would go so far as to guess that, all else being equal, the taller 
the bridge the better.  The few pianos I have, both upright and 
grand, that have bridges over 35mm in height, all have well-designed 
string scales with moderate tensions (ca. 160 lb.), and all of them 
are outstanding.

JD