[CAUT] IRe: Unison drift

[Don]

Hi Susan,

I have mentioned this before on the list. It seems to be related to the
string with the shortest distance to the tuning pin. I.E. that string will
move the most. If the pins are "staggered" the effect is even more
exaggerated. On one ancient quality upright the difference was up to 13
cents on the shortest strings, compared to the middle wire.

I've tried altering my tuning sequence (I usually do the shortest one last
on uprights) but it seems to make no change in the smearing of the unisons.

The only thing that does seem to provide a cure is a full Damppchaser
system, with back/bottom cover. After that the problem "goes away".

I have no hard data but I suspect the pin block moves causing the pins to
"flagpole" with humidity change.

At 08:48 PM 3/6/2006 -0800, you wrote:
>Dorrie, I'll be interested to see what Fred says, but I've
>noticed similar patterns after very sudden large humidity shifts.
>For instance, we had a dry sunny week, with frost in the days as
>well as the nights (not usual for us in the wintertime in Oregon),
>and then all of a sudden we got a warm wet front through (much
>more typical.) Unisons, especially on new or newly strung pianos
>went all over the place in the midrange to the high treble -- not so
>bad in the top octave. While I didn't think to diagnose the exact
>shifts, what I saw may have followed Fred's pattern.
>
>The only difference I can see between the three strings is the
>placement of the bridge pins (nearness to front edge) and the differences
>in the backlengths. As a totally uneducated guess, I'd choose the backlengths
>as the culprit, especially in the capo sections.
>
>Does anyone know about this, instead of just speculating?
>
>Susan Kline

Regards,
Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T.
Non calor sed umor est qui nobis incommodat

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