[CAUT] Stuart & Son on NPR

[Edward Sambell]

What of the effect of no downbearing load? And side bearing of the bridge pins 
exerts a twisting forse on the bridge. Alfred Knight recognized this in his 
verticals; the bass bridges have the bottom half of the bridge pins leaning at 
the opposite angle.

Ted Sambell





________________________________
From: Fred Sturm <fssturm at unm.edu>
To: caut at ptg.org
Sent: Wed, January 19, 2011 7:49:54 PM
Subject: Re: [CAUT] Stuart & Son on NPR

On Jan 18, 2011, at 8:16 PM, Ron Nossaman wrote:

> This has been addressed on Pianotech (that other list). An additional kilo of 
>agraffe mass on the bridge will increase sustain and change the tonal envelope 
>without any inherently magical properties of the agraffe.


    Just a couple thoughts about this statement: I assume it is a summary of the 
collective conclusion, essentially discounting any effect beyond that of the 
added mass.
    First, about the "extra kilo." How much does an agraffe weigh? Anybody 
actually weigh one? I am guessing somebody thought they would be about 10 grams 
each, hence a total of 880 grams added, nearly a kilo. Or does someone actually 
know? Also, does somebody actually know how much mass is subtracted from the 
bridges to install agraffes? (Or, more precisely, not included in the bridges, 
if it is a new install). Taking a normal bridge as a starting point for 
comparison, they will be machined down maybe 4 mm, so there is some wood mass 
removed, and there will be no bridge pins. If we are doing seat of the pants 
estimating, we might suppose that the agraffes _could_ weigh from 7 to 12 grams, 
and that 3 to 5 grams per unison _might_ be removed, which leaves us with a net 
increase of 200 to 800 grams round figures for the agraffe system. This is top 
of the head, just to illustrate the dangers of doing this kind of figuring 
without "getting real."
    But let us suppose that, in fact, nearly 1000 grams are added to the 
bridges. That means about a third of it will be added to the top three octaves, 
or 350 grams. Just adding 350 grams in some ways, whether a weight screwed to 
the bottom of the bridge or insertions of lead or whatever, will certainly have 
an effect on sustain. Will it be the same spreading it out unison by unison? I 
don't know, does someone else? Has it been tried? It could be, by using "earth 
magnets," that are relatively inexpensive and easily reversible (put them on the 
strings on top of the bridge).
    Without having these questions answered, and based on the physical 
experience of listening to that Baldwin retrofit, I'd have to say that I believe 
there is more to it than just added mass. Others may feel free to hold their own 
differing opinions.
Regards,
Fred Sturm
fssturm at unm.edu
http://www.cdbaby.com/Artist/FredSturm

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