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

[Ron Nossaman]

>Ron,
>
>Pitch drop. I'm referring now back to pitch raises lets say for arguement,
>especially so with new wire, adding tension causes plate compression / flex
>and an amount of board movement as your hypothesis suggests but you stated
>that you cannot account for the amount of pitch drop with only plate and
>board movement. The only other thing that can move is the string. Wire
>stretches but I'm not sure for how long.
>Hence string stretch. I'm sure there is something in the archives on this
>but for the sake of discussion I'll send it anyway.
>
>regards,
>
>Graeme Harvey

I said that I can't account for the amount of pitch drop during a pitch
raise with just soundboard deflection. The plate flexes, and there's
probably some strings rendering through bridges between the first and
second pass. The week after, I presume there has been more rendering and
equalization of segment tensions, but nothing would be sharp if the strings
were still stretching.  Strings are stretched during the pitch raise, of
course, but we aren't aware and don't much care how far they stretch
because we just pull them up until they produce the pitch we're after. Is
there long term stretch? Probably, but I don't know how much. New strings
sure seem to stretch, even when we're careful about setting coils, and
tightening those bend radii around bearing points, but they seem to
"stretch" a lot more if we don't do this, so part of that isn't stretch. So
in anything but new strings, I don't think it's much of a factor. Like you
said, I don't know for how long either.

It would be interesting to know what the creep rates are in various
diameters of piano wire under tension. Someone somewhere has surly done
some QC testing along those lines. 
 
Ron N