[CAUT] IRe: Unison drift (was Reading low humidity/seasonal SB failure)

[Susan Kline]

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
Linfield College,
McMinnville, OR

At 06:45 PM 3/6/2006 -0500, you wrote:

> > [Original Message]
> > From: Fred Sturm <fssturm at unm.edu>
> > To: caut <caut at ptg.org>
> > Date: 3/2/2006 11:31:18 PM
> > Subject: Re: [CAUT] Reading low humidity (was seasonal SB failure)
> >For instance,
> > we just had a trace of rain last night, first in months. RH rose virtually
> > instantly inside the building from 13% to 25%. I know from experience that
> > by this evening . . . most of the mid to high treble will have unison
>drift with a
> > pattern of right string 0.5 cents sharp, left string 0.5 cents flat, etc.
>
>Dear Fred,
>
>I'll bite: what mechanically would make the unison drift with that
>particular triplet pattern? I tuned a home piano this morning which was in
>exactly that situation after having been tuned at much higher RH five
>months ago. Somewhere recently I read that 'if the pitch goes out, it's the
>humidity; if the unisons go out, it's the tech.' I'm certainly willing to
>take responsibility for all the griefs of man, but it doesn't make sense to
>me that unisons going out in a very specific pattern, in a very specific
>part of the piano, would indicate poor hammer technique. When I look at the
>piano, though, I don't see what would cause the consistent flat-sharp
>changes.  Can you advise? Thanks.
>
>Dorrie Bell
>Boston, MA
>
>
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