[CAUT] Wire Stretch, was Hardness of termination vs string breakage

[Jeff Tanner]

On Apr 27, 2007, at 3:49 PM, Fred Sturm wrote:

> Hi Jeff,
> 	On the issue of stabilizing over time (not just responding to  
> humidity change and whatnot)

Yes, keeping climate factors out...

> , it may have to do, again, with low tension. The tension is  
> causing stretch (whatever the physical/metallurgical explanation  
> might be for it), very slowly, much more slowly than a string at  
> higher tension.

Yes, I agree, which is my point.

> You can often get a string to stabilize very quickly by giving it a  
> tuning to, say, 100 cents sharp and leaving it 24 hours or so. Then  
> tune to pitch, and the string will behave pretty much like its  
> neighbors, which might be 50 years old.
> 	So that low tension string just continues to stretch for years and  
> years because it has never had a chance to "get it out of its  
> system" once and for all <G>.

Yes, which is my point...

...But I was questioning your and Ron's assertion that most of the  
pitch sag is due to bridge cap crushing (even of reused bridge with  
restringing?), and bends coming into the wire as it conforms to  
bearing angles over time, and not the wire stretch you just  
described.  Do not the wrapped strings go through this same process  
also, but seem to "stabilize" long before the plain wire?  If your  
and Ron's idea that the majority of the pitch sag comes from factors  
other than wire stretch or elasticity, then your higher and lower  
tension position doesn't seem to be supported.

or vice versa?  Anyway, what you had written made an impression, and  
when I got to thinking about the differences in the way the two types  
of wire behave under the same circumstances, it made me think to ask.

I've tuned way too many pianos the last few days.
Ya'll have a good weekend,

Jeff



Jeff Tanner, RPT
University of South Carolina



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