Article about bridge agraffes - function, types

[Calin Tantareanu]

> -----Original Message-----
> From: pianotech-bounces at ptg.org 
> [mailto:pianotech-bounces at ptg.org] On Behalf Of Ron Overs
> Sent: duminică, 19 noiembrie 2006 04:25
> To: Pianotech List
> Subject: Re: Article about bridge agraffes - function, types

> 
> While Stuart claims that the bridge-agraffe is allowing the piano to 
> produce longer sustain, it is unlikely to be resulting from the 
> superior mechanical characteristics of the agraffe, when compared to 
> standard bridge pins. According to Calin's web page, the Stuart 3bp 
> agraffes weigh 12.9 grams. The total weight of these bridge agraffes 
> will add over 2.5 lbs to the overall bridge mass. I would expect this 
> mass to contribute to increased sustain in any piano. Attaching 2.5 
> lbs of brass to a conventionally-pinned bridge will also increase 
> sustain. In the case of the Stuart, with a long-bridge height of only 
> 24 mm, there will be approximately 1 lb less rock maple, when 
> compared to a standard concert grand bridge of say 34 mm in height. 
> So the overall increase in bridge mass on the Stuart concert grand, 
> due to the bridge agraffes, will likely be around 1.5 lbs.
> 
> Ron O.

I think Stuart's claim regarding longer sustain is quite correct. I heard
his piano on recordings compared with other famous concert grands. The same
piece was played on different pianos by the same pianist. The Stuart piano
struck me as having probably the logest treble sustain of them all.

I believe longer sustain is a direct consequence of using bridge agraffes,
as I tried to explain on my website and in my other replies to this thread.
Simply because you loose less energy with a bridge agraffe and put it to
better use because of its large footprint.

What I'm trying to say is that it's not only the increased mass that
accounts for the longer sustain, it is the stiffness of the agraffe which
allows it to transmit much more of the string's energy to the soundboard.
The traditional termination looses too much of it at the string/wood
interface.

The lower bridge of the Stuart is another issue. It is not directly related
to the use of bridge agraffes. I don't know why he does it.

However, mass is not the only factor when using bridge agraffes. Otherwise,
one could mass load a bridge imagine adding weights to the treble end. Maybe
they will improve sustain a bit, but not as much as a bridge agraffe,
because the string still bears on wood. And the string/wood interface is
inherently flexible and absorbs much of the string's energy rather than
transmitting it to the soundboard. The agraffe improves sustain because it
offers a clean termination, high stiffness (=little loss within it) and
transmits the string's energy via a large footprint to the bridge.
Just look at the footprint of a bridge agraffe and compare it to the
footprint of a string on a wooden cap. The difference is huge.

By the way, I'm always talking about the treble end because that is the
place where sustain is insufficient even in the best pianos.
Lower down the scale, the situation changes, as the frequencies to the
transmitted are lower and the string/wood interface becomes less of an
issue. It can transmit lower frequencies much better than high ones.

Calin Tantareanu
http://calin.haos.ro
--------------------