Overshoot -- Pitch Raising

[Overs Pianos]

Ron N, Del and list,

Ron N wrote;

>I believe the plate
>compression theory, in general, because the soundboard deflection from the
>increased tension from the pitch raise doesn't, according to my
>calculations, shorten the already tuned strings nearly enough to account
>for the pitch drop. Something else is moving, and plate compression, or
>more accurately deformation, seems like the only thing left that could move
>enough to produce that pitch drop - unless I'm missing something obvious. I
>suspect too, that there is some racking, bowing, or deflection off plane
>going on in some plate configurations, more so than in others that accounts
>for some of the differences between pitch raise characteristics in pianos
>with lighter plates. As a casual observation (otherwise unqualified), I
>seem to get less pitch drop in thicker, heavier plates in grands than in
>lighter ones. Since mounting and internal stress balance wouldn't be as
>critical in a heavily overbuilt plate as in a more reasonably adequately
>built one, it seems to me that I'd statistically see less pitch drop with
>heavier plates, though not necessarily more in lighter ones. And that's
>what I find.

I agree entirely with your theory Ron. It is unlikely that 
compression of the base metal is the cause of the drop. It is more 
likely to be plate deflection, mid section between the struts. The 
plate between the struts acts as a beam which is supporting a more or 
less uniform load across the string section. I have no doubt that the 
plate is sagging under the increased loading experienced during a 
pitch raise. This effect is most pronounced when pitch raising 
designs such as the Knight K10 vertical, which has a bar-less design 
for the entire treble. This piano is quite difficult to get up to 
pitch (much over pulling is necessary).

>  . . . . . how much of the difficulty in getting an
>S&S D to calm down with a pitch adjustment is plate flex related.

Between the plate weight (lack of) and the pin block fit (at the 
flange) - I would say 'a lot'.

The D (Hamburg version in particular) is a light plate for the (19 
ton +) string tension it supports (check out the bow of the bar 
adjacent to A1, when at pitch). An additional stability problem with 
the Ds is that the pin block fit to the plate flange is nearly always 
poor - this becomes a major problem when the pin block is un-bushed, 
as it is in Steinways (check out the fit of the pin block to the 
flange with a mirror and a light from underneath). I have found that 
replacement pin blocks in Ds, which have been properly chalk fitted 
along the entire length of the plate flange, result in much improved 
tuning stability.

Seasons greetings and regards to all,

Ron O
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Website:  http://www.overspianos.com.au
Email:      mailto:ron@overspianos.com.au
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