[CAUT] pre-stretching new string?

[Fred Sturm]

On 6/7/07 5:13 PM, "Ron Nossaman" <rnossaman at cox.net> wrote:
> 
> That was Darrell, and his premise was based on strings not
> rendering through the bridge. An interesting thought though.

Yes, an interesting thought as a component of what happens. But as I worked
through it in my mind, the friction would eventually give way, strings would
render, and you'd end up with the original tension, and a longer speaking
length to boot (so you might even expect lower pitch). One would predict
that one could manipulate the wire (push on it in the speaking length) to
equalize the tension, and so strings that had gone sharp could be fairly
easily made to get the string back to pitch. Or do it by vigorous pounding.
Tried that and that, didn't happen.
    Also, part of Darrell's thesis was to "prove" that bridge rise (caused
by soundboard expansion - increase crown) couldn't account for pitch rise,
using calculations. He came up with a calculated bridge rise of .5 inch to
account for observed pitch change. There were typos, and, I think,
miscalculations. I think the calculations based on the distance between
tuning pin and hitch pin (based on changes in deflection) are far more
reliable and closer to real life. My own empirical experiments showed that
0.1 inch rise in string deflection would yield a pitch rise of 15 - 30
cents.
> 
> Nothing is simple or isolated, and this isn't a discussion on
> every potential detail of why and how pianos go out of tune,
> is it? My initial intention was to illustrate that string
> stretch wasn't the likely primary reason for long term pitch
> drop. I don't have authoritative details on everything that
> happens in soundboards with moisture changes, and most likely
> never will. I've picked up what I think are a few clues, and
> reported why I think so. That's the best I can do.
> 
Yes, I understand that. And your thoughts about bridges, bridge pins,
angles, and so forth are excellent and make a whole lot of sense. I'm just
balking at your more "absolute" seeming statements, like
>"Hasn't it already been determined fairly reasonably that soundboard rise, or
>fall, isn't a significant (there's that word again - not absolute or
>exclusive, even if measurable) factor in pitch change?"
I'm perfectly willing to go along with a statement that probably bridge
changes are actually more important than soundboard rise or fall, but I'm
not willing to discard rise or fall as not being "significant" until I have
seen that proved in some fashion. All right, "significant" is an inexact
word, but your own calculations show that a .6 degree change in downbearing
(soundboard rise/fall, perhaps) is equivalent to your measured and
documented .2 mm expansion in bridge. Now, you say you have never measured
more than .5 degree, but wouldn't that .5 degree change be "significant,"
nearly as significant as the .2 mm bridge expansion? Maybe it is clear that
the bridge contributes more than the soundboard, but the soundboard may
still contribute a good bit. Could be 60/40. Or 70/30. I'd call the 40 or 30
significant.
    My experience tells me the grands at UNM with dry humidistat and a 50
plus a 25 watt rods change pitch about half or less as much as those
without. Lids are almost always up. Air is in constant motion from the HVAC
system. I'm real skeptical that enough moisture is pulled from the bridges
into and through the soundboard to overcome what is being absorbed into them
from the air. Or that the heat from the rod raises the temperature of the
bridges through convection enough to do the same. Maybe it's true, but my
common sense notion is that most of what I am affecting with my rods and
humidistat is the board.
> When it rains outside, the humidity level in my house
> increases even though the doors and windows are closed.
> Dampp-Chasers are least effective when the lid is always wide
> open, with no bottom cover, and most effective with a top and
> bottom cover.
Very true, and I a pretty well convinced by your writings that the reason DC
systems work less well than expected often is that the bridges are exposed.
I haven't got around to fooling with top covers yet. I have, so far, found
bottom covers less effective than I would have liked to expect. Effective,
but somewhat marginally in many cases. I'm wondering if I can work out a way
to manufacture string covers using material similar to bottom covers without
overmuch time and hassle. One of these days . . .
> 
> Ron N
> 
Thanks for your thoughts.
Fred