tapping strings

[David Skolnik]

At 06:49 AM 04/04/2002 -0600, you (Ron N) wrote:

>I've gone over this a bunch of times on Pianotech. Check the archives under
>"string seating" and such. Meanwhile, here's a clip from the most recent
>round...

Ron N-

Since you seem to have the info easily at your disposal, could you please 
give me the names and dates of at least a few of these threads, such as the 
one from which the clip below came from?  When I tried using the search in 
the archives I got very little.  I'm search impaired.

The implication of your line of thought, which, for the most part, I agree 
with, is that even a correctly set up (downbearing-wise) piano in a 
temperate climate with x amount of humidity variation will soon exhibit 
some degree of negative front "termination", the cause of which tapping 
will not cure.  It seems to me that, if you discount, for the moment, any 
distorting interaction between the string and the flat spot formed on the 
pin, then, from a termination point of view, you have negative front 
bearing. The string energy, or some portion of it, is going into the pin. 
Some residual energy will be absorbed/reflected by the wood. What changes 
between this scenario and one in which the negative condition is more 
pronounced would be the alteration of loading forces on the bridge/board. 
So, your tendency, in a negative front condition would seem to be to let 
the string seek its own point of vertical termination stability, or, that 
defined by the point where the string does contact the bridge proper, but 
which then allows some vertical displacement at the pin when it (the 
string) is vibrating. You can correct me, whether I'm wrong or right.  Can 
you describe a situation  where the crushing of the bridge surface, 
especially at the termination, could be eliminated? How might a less 
resilient material affect the tone, or life of the string?

David Skolnik





>------------------------------------------------------------------------------
>My point here is that strings don't hang up on bridge pins in the first
>place, so seating them back down isn't curing anything. Sure, they move,
>ping, and seem to have been up the pin before seating, but I think that's
>just because we're not looking past a basic false assumption (yet again).
>Here's the scenario according to the way I see it.
>
>Incidentally, this does assume a reasonably well set up piano with positive
>bearing at both the front and back notches and the notch edges remotely
>centered on the pins - for simplicity's sake.
>
>During the wet cycle, as the swelling bridge is pushing the string up the
>pin against down bearing, side bearing, and pin inclination, the wood
>surface of the cap is crushed under the string. Since the most resistance
>the string offers to being pushed up the pins happens AT the pins, rather
>than in the center of the cap, the cap edges crush more than the center.
>The string is no longer lying on a flat cap. This is important. In the dry
>cycle, the soundboard crown is less, the bridge is shorter, so the
>downbearing angle is less across the bridge. At some point, it's likely
>that the string isn't touching the bridge surface at the edge of the notch
>where the pin is, but it is touching a little further back on the bridge
>because the edge is crushed down below where the pin inclination can force
>the string under tension. The string hasn't climbed the pin. It's
>horizontal termination support just no longer coincides with the notch
>edge. If the pin is even a little loose at the bridge surface, it will
>flagpole and produce false beats. Seating the string will knock it down on
>the bridge, creating a slight negative front bearing angle between the
>speaking length and the length of string that wasn't touching the bridge
>prior to seating. The false beat may go away temporarily, but it isn't
>fixed, and will return as the piano is played and the string tries to go
>back to it's natural straight line between termination points.
>
>The false beat is there in the first place because the bridge pin is loose,
>the bearing angle is low, and the cap is deformed so the horizontal
>termination point is behind the (-20°) vertical. The notch in the pin may
>eventually be a factor, but these kind of beats will often show up very
>early in a piano's life before any significant wear damage accumulates on
>the pins.
>
>Seating strings won't cure any of these conditions, so why is it so
>universally insisted upon? It's quick, easy, and gives the immediate
>illusion that the tech is improving something. At least that's why I used
>to do it before I decided it wasn't a long term fix.
>-------------------------------------------------------------------------
>
>That's the gist of it. When a tech can touch a screwdriver to the side of a
>bridge pin opposite the string and make the false beat disappear as long as
>a light pressure is applied (never touching the string directly), what
>indication is there that seating the string will fix it?
>
>Ron N