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MMD > Archives > August 1997 > 1997.08.16 > 06Prev  Next


String Tension
By Craig Brougher

Bernt Damm, in referring to piano strings, made this comment:

> From practical piano-building, I know that a music wire sounds at its
> most pleasant to the human ear just before its breaking point.  Good
> pianos are therefore constructed in such a way that the wire is under
> such tension that it almost (not quite) breaks.  The wire will continue
> to sound at its best as long as the pitch of the instrument (tension)
> is not lowered too much.  Experiments have shown that not even surface
> rust on the steel makes a noticeable sound difference to the string
> in a piano.

I agree that rusty strings in the trichord section have no effect on the
tone of the string at all, however, the advantage to restringing the bass
section, tone-wise, is all important.

The bass strings comprise the "foundation tone" of the entire piano.
Live bass strings resonate with every other string, even through their
dampers to a degree, lending both the fundamental plus the higher
partials that characterize the piano's personality and power.  Old bass
strings cannot do that to a great degree, and that's why old string sets
sound "tubby."

Another advantage to replacing the bass strings (and bushings and pins,
too) is to see if you can remove and replace the bass bridge in uprights,
as well as to make needed repairs down there.  The bass bridge is
cantilevered for tonal balance, but this also causes high shear forces
which tend to break the joint, and is very prevalent in upright pianos.

About the string tension in most pianos, I think you will find their
treble pulled up to within 45-60% of their breaking strength, usually.
Granted, a few high-tensioned pianos tune within 70% up there, but that
is unusual.  Tenor sections are tensioned between 25-40% on average.

Most upright pianos (which are lower tensioned than most grands) can
be purposely tuned up 5 half-steps without breaking any strings, since
5 half-steps changes the tension only about 35% or so.  Just for fun,
try it on an old instrument which you intend to re-string, and see how
far you can take a few strings, just for a test.  Pianos aren't that
fragile.

Craig Brougher

 [ I don't like the sound of the high treble section in the new, big
 [ Boesendorfers and Yamahas.  To me, the tone-purity has been sacrificed
 [ by demanding so much power from the partials, which sound quite
 [ atonal to my ears.  Is that due to the great tension or the hammer
 [ characteristics, or what?  (Or is it my ears?)  -- Robbie


(Message sent Sat 16 Aug 1997, 13:41:59 GMT, from time zone GMT.)

Key Words in Subject:  String, Tension

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