Stretching

[EHILBERT@midd.middlebury.edu]

Merry Christmas and Happy New Year to you also, Avery
      Yes, that is why lowering pitch is as tricky as raising it, things
are definitly adjusting anytime you are making a substantial pitch change.
Just as increasing tension on a string will increase the downbearing pressure
on the bridge so will lowering tension.  With an increase or decrease in tension
several things can happen to affect the pitch of adjacent notes.  First, the
board will fo up or down slightly and that movement will affect the other notes
in that area.  Likewise, as a piano gets older, the strings do not render (move)across the
bridge very much.  Thus the bridge will move slightly forward or
backward depending on whether the tension is increased or decreased in the
speaking length portion of the string.  That too sill change the pitch of the
adjacent strings.  Steve Fairchild once said in a class that the plate also
compresses and that can change the pitch of adjacent notes.  Perhaps it can.
At any rate, things are definitly moving and several tunings may be needed to
make things stable where you want them, especially in the high treble.
      As a side issue on making major pitch changes, I believe this to be one of the major
causes of bridge roll in pianos.  If the strings don't slide over
the bridge easily, and if the pitch is raised considerably, then the bridge
will be pulled forward as the overall system attempts to equalize the tension
throughout all parts of the string sections.
      While touring factories in Germany se saw one factory that put
screw adjustable supports between the bass bridge and the plate when stringing
inorder to prevent the bridge being pulled forward.  I have pictures of this
in my slide collection but don't know exactly where at the moment.  I am not
sure, but I believe this was being done in the Seiler factory.  Maybe
someone else from the tour remembers.  Yat Lam Hong might very well!
      At any rate, it does lead one to think about what is happening to
the bridge and soundboard when making a large pitch change on an old piano.
Scott Jones, in a Steinway class, showed a techniques for equalizing the
tension on both sides of a bridge through the use of a string hook and
pulling on the string next to the bridge so as to increase the tension
enough to draw more tension into the waste end of the string.  I have done this
several times and I do believe it helps to stabilize the pitch.  I also
believe it would help to stop bridge roll and thus help to protect the
string/bridge/sounboard geometry.  Should help to prevent sine-waved boards
also.
      I would be interested in hearing others thoughts on this.
Ed Hilbert
VT Chapter
EHILBERT@MIDDLEBURY.EDU