String Leveling

[Delwin D Fandrich]

robin fox wrote:
> 
> I too have been reluctant to level strings despite what I read (persistent cuss
> that I am). My thought has always been that the hammers would have mated to the
> string heights so that leveling them would disrupt that relationship. So what
> does happen to the string-hammer relations on leveling, or, why does it work?
> 
> Robin Fox

Robin,

Boy, do I ever wish I had an answer for this! But I don't. I do have a
couple more questions, though:

  1)  Not all of the unisons with strings that are out of level make any
abnormal sounds whatsoever. Why not?

  2)  If it is a hammer contact, or impact, or release problem then why,
if the strings are out of level and the hammer is carefully shaped to
fit the strings, does the sound often still sound “twangy.” Or it can be
fine. I've seen both. It would seem that if the problem were simply one
of the hammer hitting all of the strings simultaneously, then fitting
the hammers to the strings would take care of the problem in all cases.
It doesn't.

  3)  The explanation is given that the obnoxious initial sound we hear
from out of level strings is due to their starting to vibrate out of
phase and then being brought in phase during the first few milliseconds
of operation by mutual coupling. And that to get them to vibrate in
phase from the start requires that the hammer strike all three strings
simultaneously. Actually, the assumption is made that if the hammer does
strike all of the strings of a unison simultaneously then all of those
strings will be vibrating in phase and the problem will not rear its
ugly head. (See Ed Foote’s post on this subject.) And this explanation
certainly seems to make a lot of sense. However, the vibration patterns
and modes of piano strings are exceedingly complex. They don’t just
vibrate in a vertical and horizontal plane; there is also a rotational
mode and a longitudinal mode. In the real world, with all of this going
on simultaneously, the separate strings of a unison rarely, if ever,
vibrate precisely in phase. They are certainly not in phase if any one
of the unison strings is even slightly—and I do mean “slightly”—out of
tune. Also, it should be remembered that you don’t hear this same twangy
sound as the open string catches up with the other two when the piano is
played with the una corda pedal depressed. Nor for that matter, with the
Bluthner treble aliquot string. In each case, the unstruck string
certainly starts out out of phase.

  4)  Why do out of level strings create more tone problems in some
pianos than in others? There are a few pianos that seem to be almost
completely impervious to the effects of out of level strings. This has
lead me to wonder just what specific design features might accentuate or
suppress these particular problems.

I have no solid answers to any of these questions. I can say, however,
that I’m not really looking at the hammer impact phenomenon as much as I
am at string termination. When you “level strings” what you are really
doing is more precisely seating the string against its termination
point—at least you are changing the configuration of the string at that
point. You are also decreasing its bend radius at the point of
termination which has to affect the amount of energy that is coupled to
the front scale.

Well, I have to get to work now. By tonight I expect some technical
wizard will have supplied solid answers to all of these questions. By
then, I should have a few more...

ddf