String termination question

[David Love]

Like Ron said, termination of the bridge top and pin need not be exactly the
same, in fact, it's probably best to err on the side of having the notch cut
slightly behind the pin to prevent the edge from migrating out beyond the
pin over time as the bridge top indents underneath the string.  With the pin
angled at some 20 degrees the string will not ride up during its normal
vibration and create problems as you describe.  Bridge pins are necessary to
prevent lateral movement of the strings especially since the hitch pins are
not always in an exact straight line with the bridge notch.  With single
strings on a guitar, you don't have that problem.   The bearing angle
through the capo (or the pressure bar) lessens the need for pins on that end
except, such as in the bass on certain uprights, where the tuning pin
location creates an offset.  BTW, a lack of adequate counterbearing through
the capo can create problems with string migration side to side as you see
on some lesser uprights and grands, especially if the layout of the tuning
pin array doesn't quite match the needed spacing of the strings across the
capo.  

 

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 Geoff Sykes
Sent: Sunday, January 13, 2008 10:51 PM
To: 'Pianotech List'
Subject: RE: String termination question

 

David --

 

I believe I used the term inharmonicity incorrectly. My apologies.
Inharmonicity is caused by the fact that the string doesn't terminate at an
exact or perfect point like, say, a hinge, but rather through a bend that
does not uniformly reflect the multiple waveforms of the different partials
created within a vibrating string at a unique point. 

 

I don't think the primary purpose of a bridge pin is to prevent the string
from sliding around on top of the bridge. Like a guitar or other stringed
instrument that possibility is minimal. But just the same, because of the
high tension and subsequent high partial content of a piano string the
tolerance of any string movement across the bridge would be much lower and a
bridge pin is very helpful in that regard.

 

What I'm referring to is the need to make sure that the edge of the notch on
the bridge exactly matches the side of the bridge pin so that the string
termination at the bridge is the same in both the X and Y axis. If it were
not the same then the string is literally a different length on one axis
than it is in the other. Since a string moves in all directions when
vibrating, not just up and down, if that termination is not exact then the
partials created in one axis are different than in the other, creating
beats. This is one reason why we make sure strings are seated correctly
against the bridge itself, and hope that the bridge notching and the pin
placement has been done accurately. It's another reason, in addition to
stability, why the movement of bridge pins in cracked bridges is such a
problem.

 

So I understand why matching the termination points for both X and Y axis is
important at the bridge. What I don't understand is why it's not a
consideration at the opposite end of the string. And like I said, since this
is a centuries old practice it's obviously not a significant problem or else
we would see X and Y axis termination at both ends of the string. I'm just
curious as to why it's not a problem at the agraffe and capo bar end of the
string. 

 

For a better understanding of my question check out Reblitz page 113,
"Ringing, Jangling or False Beats in Treble Strings." I pulled out my copy,
(2nd ed), and looked this up and then posed my question here because Reblitz
just didn't address the effectiveness of the agraffe/capo bar termination.
Perhaps, as you suggest, it's because the counterbearing is so severe that
it's just not a problem. I'd just like to understand it a little better. If
that's possible.

 

-- Geoff Sykes, Los Angeles

 

 

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