plate reaction was Re: Pitch Raising to A440.......Or Not?

[sid blum]

Sid Blum
sid@sover.net
----- Original Message -----
From: Ron Nossaman <RNossaman@KSCABLE.com>
To: <pianotech@ptg.org>
Sent: Sunday, August 19, 2001 1:58 PM
Subject: Re: plate reaction was Re: Pitch Raising to A440.......Or Not?


> >After raising pitch 50-100 cents,and leaving the piano at 440 I usually
> >expect the piano to drop and need another tuning within a few weeks.
Does
> >this suggest that I am missing something?
> >
> >Sid Blum
>
>
> Hi Sid,
> Obviously, something is moving, but why does it have to be the plate
> flexing?

Sorry, didn't mean to impy that here...hope I didn't seem inflexible...

>When you raise pitch 100 cents, you most likely aren't going to
> get tensions in the string segments fore and aft of the bridge equal. Over
> time, temperature, and humidity changes, the string will tend to render
> through the bridge gradually until those fore and aft tensions are pretty
> close. Since you pulled the segments between the bridge and pins higher
> than they were, the segments between the bridge and hitch will probably be
> of lower tension that what you just tuned, so the pitch drops at the back
> scale steals tension from the speaking length (etc). If you leave more
> tension between the agraffe and pin than there is in the speaking length,
> the pitch may go high first (since there is less friction at the agraffe
> than at the bridge pins), then low later as the string slowly renders
> through the bridge.
>
> Anyway, that's my take.
>
> Ron N

Makes all kinds of sense.  But in the case where after a couple of weeks the
unisons are better than I expect and the pitch has dropped most in the mid
treble  always assumed that the board and maybe the entire structure was
moving around.  Don't mean to harp on this subject, I'm just thinking about
all the variables involved in predicting, for the customer's benefit, when
to plan on a follow-up tuning.

thanks,

Sid Blum
sid@sover.net