Drifting Unisons

[Newton Hunt]

The flat and sharp strings would reverse themselves if this were the
case.

		Newton

Jon Page wrote:
> 
> Could it be that the wire on the treble & bass sides of the unison
> react to the movement of the sounding board. I always thought it
> was one of those mysteries of nature.
> 
> Still do,
> 
> Jon Page
> 
> At 03:15 PM 11/07/1999 +0000, you wrote:
> >Ron,
> >       I agree we would have to account for the total "waste length" of
> every
> >string (whether toward tuning pin or hitch pin), and their relative
> >tensions, and the amount of friction involved, and bridge rise and roll,
> >to come to a complete analysis. I have certainly considered all these
> >factors in my musings while pitch raising/lowering for the ?thousandth
> >time.
> >       The puzzle for me is that uprights and grands both show the same
> >tendency for the right string to move most, whether to a large or small
> >degree. Hitch pin waste lengths vary, but typically not by much on any
> >given piano. Tuning pin waste lengths vary pretty consistently, so that
> >on all grands the right tuning pin's waste length is longest for the
> >unison, while on an upright the right is shortest. So why isn't the
> >pattern reversed for uprights?
> >
> >Fred
> >
> >Ron Nossaman wrote:
> >>
> >> Hi Fred, I doubt that this will answer anything well enough to clear this
> >> up, but here are a few observations.
> >
> >> * Let's consider what we are looking at. There is more involved than just
> >> the strings from the bridge to the tuning pins. You need to consider the
> >> entire string length from the hitch to the tuning pin. When the bridge
> >> rises and lowers with the soundboard, the strings render over the rear
> >> aliquot, the V bar, the front counter bearing bar(s), and, unless the total
> >> length of string segments behind the bridge equals those in front of the
> >> bridge, the strings will render through the bridge pins to some degree. The
> >> bridge is the high friction point, so it takes bigger tension changes to
> >> move a string across it. In general, the longer the total string length is,
> >> the less the tension change with bridge rise or fall (not roll). The left
> >> string of the unison has the shortest length from the bridge to the tuning
> >> pin, but not necessarily from the tuning pin to the hitch. This will change
> >> from unison to unison depending on the distance from the bridge pins to the
> >> hitch for any string. If the total back scale is significantly shorter than
> >> the total front scale, here's what should happen when the soundboard and
> >> bridge rises with humidity increase: The tensions in the back scale will
> >> increase as a faster rate, and peak at higher values than the tensions in
> >> the front scale segments. If the difference in tension is enough to
> >> overcome the friction at the bridge, the string will render across the
> >> bridge toward the hitch pin, further raising the tension in the front scale
> >> as the back scale tension decreases. The pitch rise of the speaking segment
> >> in this instance will end up being sharper than that of a string segment of
> >> a neighboring unison who's tuning pin is closer to the capo than this one
> is.
> >>
> >> Just like everything else in a piano, you have to take fourteen different
> >> things into account to make any sense of what you're looking at. After you
> >> factor in the string segment lengths, proportions of front segments
> >> relative to rear segments, vertical bridge movements, and friction, it
> >> begins to make some sense. The biggest problem as I see it is that we can't
> >> really know what the tension is in any given section at any given time (or
> >> can we?). If we could measure segment tensions we could see exactly what's
> >> happening.
> >>
> >> Ron N
> >
> Jon Page,  Harwich Port,  Cape Cod,  Mass.  mailto:jpage@capecod.net
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