String termination question

[Geoff Sykes]

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
 
 
 

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of David Love
Sent: Sunday, January 13, 2008 8:34 PM
To: 'Pianotech List'
Subject: RE: String termination question



Are you asking why there aren't pins at the capo bar (or agraffe)?  Part of
the reason there are pins in the bridge is to keep the strings from moving
sideways.  The relatively low bearing on the bridge (as compared with the
counterbearing angle for the agraffes or capo bar) combined with the bridge
surface's natural lubricity would allow the strings to move side to side
quite easily especially as the bridge moves up and down.  You don't want
that.  You might note, however, that on guitars and other stringed
instruments, the strings are not locked into place with vertical pins at the
bridge and they don't seem to move.  Anyway, the same problem doesn't exist
at the capo or agraffe though leakage can occur where counterbearing angles
are insufficient.  

 

Changing lengths, btw, will not necessarily cause an increase in
Inharmonicity, rather a difference between similar strings.  Also, bass
string do exhibit a tolerance for different speaking lengths (and different
winding lengths) without causing problems with Inharmonicity as evidenced by
the number of pianos in which the bass bridge is not individually notched
for each set of unisons.  

 

Of course, I'm not sure if that's what you are talking about.

 

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 8:05 PM
To: 'Pianotech List'
Subject: RE: String termination question

 

Wim --

 

BUT... As I understand it, one of the important reasons for the X and Y axis
to terminate at exactly the same point, (at the bridge), is that if one axis
is different than the other then the string is essentially a different
length in one axis than the other. This increases inharmonicity and causes
conflicting partials in the two axis. This is a similar reason as to why the
windings on bass strings must be the same length and end at the same
distance from BOTH termination points. I understand that, among other
things, equal termination at the bridge equates to maximum transfer of
energy to the soundboard, but doesn't unequal termination at the agraffe or
capo bar cause distortion in the string waveform that not only increases
inharmonicity and unwanted conflicting partials but also a loss in overall
energy?

 

I don't mean to start an argument. I'm really just interested in the
mechanical logic of this centuries old manufacturing practice. For all I
know the contribution of any errors at the agraffe or capo bar may be so
insignificant as to be unworthy of consideration. I'm just curious. 

 

-- Geoff Sykes, Los Angeles

 

 

 

 

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Willem Blees
Sent: Sunday, January 13, 2008 7:22 PM
To: pianotech at ptg.org
Subject: Re: String termination question

Geoff

 

As Annie indicated, the string needs to go over the bridge for the
vibrations to transfer from the string to the soundboard. The string needs
to be seated at both sides of the bridge, so that the vibration is
transferred without interference. If the string is not seated, then there
will not be a solid transfer of the vibrating string. 

See what happens when you start thinking.  :
<http://o.aolcdn.com/cdn.webmail.aol.com/33706/aol/en-us/images/aimex/cry.gi
f> 

Willem (Wim) Blees, RPT
Piano Tuner/Technician
Honolulu, HI
Author of 
The Business of Piano Tuning
available from Potter Press
www.pianotuning.com



-----Original Message-----
From: Geoff Sykes <thetuner at ivories52.com>
To: Pianotech at Ptg. Org <pianotech at ptg.org>
Sent: Sun, 13 Jan 2008 3:42 pm
Subject: String termination question

Greetings All --

 

I made the mistake of thinking the other day, and I started wondering why
piano strings are terminated at the bridge on both the X and Y axis but at
the capo bar, or agraffe, on only the X, (or perhaps that's Y depending on
how you are looking at it), axis. We go to lengths to make sure the strings
are seated properly at the bridge so that there is a definite and precise
termination in both planes at the bridge and bridge pin. Why then is the
lack of termination in both planes not a problem at the agraffe and capo bar
end? 

 

-- Geoff Sykes, Los Angeles


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