Strings riding up (was Tuning stability)

[Ed Sutton]

Fred wrote:

>    I am thinking in practical terms: if one chooses (as I do) to resurface the
bridge
> top, re-notch and repin, should one make a great effort to get the top back to
> flat? Perhaps not. I will theorize that a curved profile will work just fine, as
long
> as, using the string test, a string run from capo or agraffe touches front of
notch
> before the rest of the bridge top. In fact, maybe a mild curvature would be
better
> theoretically, both for transfer of energy and for durability. Possible, I'm not
> saying it's so.

If strong contact with the bridge top at the pin matters, then we should be
carving a gully in the middle of the bridge cap so that the strings only contact
at the front and rear bridge pins!

But that is where we need some amazing videos showing us what the string really
does at the bridge pin.  Is it possible that some wiggle room behind the bridge
pin is both inevitable and beneficial?  It would make the termination more hinge
like, and presumably lower the inharmonicity.  Is it possible that there is a
continuous rattle going on just behind the bridge pin, but it is so high frequency
that we don't hear it?  Even if we get perfect termination, and that prevents the
string section beghind the pin from moving down, there is nothing to prevent it
from flexing up when the speaking wave is down. Since the bridge pin is slanted, I
assume the wave is reflected at an angle that progresses with each return of the
wave, and that the string behind the pin is sort of spinning.  I also wonder if
the increasing width of the groove we see near the pin may be caused in part by
string movements.

(If anyone thinks I've gone nutty here, please explain.)

There is plenty wiggle room in all front terminations, and they still seem able to
reflect a wave.


>    How is load transferred through bridge to board? On violin family
instruments,
> the bridge top is as close to a point as practically possible. Harpsichords (not
> counting 20th century anachronistic designs like Neupert and Sabathil) have
> the string bearing on a mild point of the bridge, 1 - 2 mm behind the bridge pin
> (with a definite gap between). The flat bridge top is definitely a piano thing,
and
> probably mostly by accident of practical considerations (planes make flat
> surfaces).

Has anyone written a history of the harpsichord and piano bridge?  There will
always be a dialectic between acoustic needs and production driven designs,
especially as the piano becomes mass produced.



>I'm thinking that, although I have believed, like others, that the
> process of resurfacing doesn't affect downbearing, because one is only
> removing material to the bottom of existing grooves, perhaps this isn't really
true.
> One may be reducing the loading of the bridge a wee bit by removing the
> curved part in the middle of the bridge.

How much wood are you removing?  I think this would be very slight.  When I
resurface a bridge I want the string grooves to still show very slightly because I
believe the compressed wood is more stable than new wood. (Sometimes the string
groove barely disappears in the middle of the cap.) Because the old groove has
already been compressed, and also because I epoxy the new pins, in the style of
Bill Spurlock's articles, I believe my resurfaced bridge top is more stable than a
new bridge top.

Ed Sutton