Pitch Raisins

[Dean L. Reyburn, RPT]

Dean Reyburn wrote:
>:My experience, and that of many other RPT's indicates that raising the
>:center strings first, and then the left and right strings later results
>:in *LESS* tuning stability than if you just pulled up the unisons as you
>:go.  I have not researched the stability aspect with hard data though.
>:
Ron Nossaman writes:
>The term "stability" is tossed about here without defining the term.
>Stability should, in my mind, refer to the long term probability of any
>given note, or overall tuning, staying where you LEFT it when the tuning was
>done. This is, as opposed to, an individual note or section drifting with
>soundboard deflection as a bridge is loaded during a pitch raise.

That's as good of a definition as I've heard.  Yes I would agree, the
pitch drop in a pitch raise (or lower) happens immediately, and is
separate from stability, except as noted below.

Ron:
> What happens during the pitch raise has nothing to do with stability.

Well for the most part that's true, but there is one effect you might be
overlooking.  When you raise the pitch on all the center strings first,
you will have to overpull the first string quite a bit more than you will
the second string of a trichord.  The third string of the trichord will
need very little overpull.  This may be why pitch raising chromatically,
unisons-as-you-go ends up more stable.  Each string is pulled almost the
exact same amount above pitch.  There is a string-stretching factor that
enters in to the equation, similar to the effect of pulling a brand new
string up to pitch.  This effect is more pronounced on pianos that are
way of pitch, say 100 cents or more.

>String breakage incidence goes up with the amount of overpull. The reason
>overpull and resultant string breakage is higher when starting in the middle
>is that this is the center of the board and will deflect further during the
>pr than any other portion of the board. Starting at A1 and progressing
>sequentially to C88 loads the board from the edge (which doesn't deflect as
>much with a given load) to the center (which has already been forced down
>somewhat by the already tensioned strings). The result is that the overpull
>is less and string breakage goes down accordingly. From the center out, the
>soundboard acts like a class two lever, for instance a wheelborrow. In this
>analogy, the rim is the wheel, the center is where you grab the handle, and
>the load goes in between. My guess is that the results of an "edge first,
>center last" pitchraise procedure would be even better if you were to
>alternate from both ends and work toward the center tuning the unisons as
>you go. It would be pretty slow, but if any of you digitoids out there in
>electronicland have ever tried, or would care to try it, I'd be curious to
>know how it works. I'd try it myself, but I don't have access to the
>hardware (it's tough to do with a fork <G>).
>
That is a real interesting analogy, will have to think on that one.  It
sounds like a fascinating experiment too.  Seems like a good way to do it
would be with two (human) tuners with two Accu-Tuners starting at each
end.  Sounds like fun.  If nothing else, the piano would get raised twice
as fast!  ;-)

But seriously, I hadn't thought of it like that.  I pitch raise
chromatically, unisons-as-you-go, and think of it as sort of a tension
"wave" that moves up the piano with me.  The peak of the tension "wave"
is on the notes I just raised, and the valley of the "wave" is just ahead
of me.

BTW, I tried my own experiment I posted a few days ago:
>If anyone doubts this [pre-drop effect], try this experiment:  on a piano
that is say 50 >
>cents flat or, measure the pitch of middle C (C4) with a electronic device.
Now pull the
>strings up to pitch starting with the lowest A up to the B below middle C
(B3).  Use
>whatever overpull you would normally use, or use none if you want.  When you
get to B3, and
>before you tune C4, measure C4 again.  You will find it to be MUCH lower in
pitch than it
>was when you started pitch raising.

The piano was a Yamaha G2R 6 years old, not tuned for 5 years.  It varied
from about 80 cents to 120 cents flat.  Middle C (C4) measured 100.3
cents flat.  After pitch raising all the strings from A0 up to and
including B3, C4 had dropped 12.5 cents to 112.8 cents flat.  I used
12.5% overpull (10 cents max) on the wound strings, and 30% overpull on
the plain strings up to B3.  The piano ended up within 2-3 cents on
almost all notes after one pass.  (no broken strings - but it was pretty
new)

Did anyone else try this?  I would be interested in the results.  Every
piano will be a little different.

Dean

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Dean L. Reyburn, RPT                    Sanderson Accu-Tuner
 REYBURN PIANO SERVICE, INC.             Authorized Distributor
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