termination & differences in string pull/pin set

[Delwin D Fandrich]

Rolf von Walthausen & Nancy Larson wrote:

> The specific situation I'm trying to figure out has to do with a Baldwin
> SD-10 from the early 70s that was restrung five years ago with the original
> 'treble resonators'.

These devices are actually string termination pieces.  They are not
"resonators" in any sense of the word.  They were developed to provide a more
precise string termination point and to couple the Capo d’Astro bar to the
pinblock plate flange.  The idea was to make the Capo d’Astro bar stiffer -- to
raise its mechanical impedance -- and make the string termination more
efficient.  Unfortunately, the string deflection angles are too shallow to
efficiently terminate the strings.


> Nothing else was modified as far as I can see.  The problem is that the
> strings in the treble section D5-G6 do not move in corresponding units with
> similar movements of the pin.  The feel and response is much like that of a
> Steinway upright where the string moves a large amount all of a sudden after
> many movements of the pin in the block.

The pins and strings react similarly in both pianos for much the same reasons.
The string deflection angles are not sufficient to adequately terminate the
speaking lengths of the strings.  There is very little friction across the
string bearing points.


> I've never experienced this before on an SD-10, either with the old-type
> resonators or the new type.  I was interested to read Roger Jolly's
> observation that the 'old-type' resonators were made of a material with a
> different carbon content and hardness, so I wonder if there were
> experiments with different prototype models of SD-10 (between the SD-10 and
> SD-10b) with resonators that might be causing the strings to respond
> differently to string pulls?

The design is particularly susceptible to string noises.  Making the part of
harder material has helped but not eliminated the problem.  To eliminate the
problem will require a redesign of the part.


> I'm thinking how tuning stability is related to changes made to the capo
> and other termination points.  What, if any, changes in string pull or
> tuning pin setting has anyone experienced after making
> changes/modifications to the capo bar and/or other termination points?

Well, it's a trade-off.  There must be some string friction at the bearing
points.  Too little and tuning becomes a problem because the string is too
sensitive to  even slight movements of the pin.  Some of the Steinway 1098's I
worked on during the 70's could be put out of tune by just putting a moderate
finger pressure on the tuning pins.  A tuning hammer was not needed.  On the
other hand, some of the old M&H grands used such extreme string deflection
angles that the pins had to be turned substantially before the string could
render through.  The strings often break before this can happen.  A similar
problem exists -- but for a different reason -- with the Steinway style of
tenor string counterbearing scheme.  In these pianos the string is passed over
a broad expanse of felt between the agraffe and the tuning pin.  The problem is
exacerbated as the piano ages and the strings take on a bit of surface
corrosion.  Friction quickly increases to an unacceptable level.  Replacing all
this felt with a simple brass half-oval makes the piano much easier to tune
through this section.

Del