[CAUT] Wire Stretch

[Ron Nossaman]

> I have a different thought. Picture this:
>       The piano is tuned evenly but is 5 cents below pitch (440). The 
> tension on all string segments are equal.
> I am going to use the term render to descibe the equalizing of tension.
>       
> You start to tune, raising pitch, If the string doesn't render across 
> the bridge, wouldn't the bridge roll forward as all the strings were 
> brought up?
> 
> Keith Roberts


One would think, though not necessarily during tuning. A five 
cent pitch raise won't pull a bridge forward that much unless 
the back scale is very long, and those strings that don't 
render through during tuning will some short time later, and 
the bridge will go back. That strange random minor unison 
detuning that happens a few weeks after that 10-20 cent pitch 
change could very well be from this cause.

As I've said a time or 600, the string is moved up and down 
the pin by dimensional changes of the cap. If the string moves 
up or down, it will also render through while the friction is 
overcome by the vertical movement, so the back scale should be 
fairly close, above or below, to the tension of the speaking 
lengths most of the time. Not exact, but fairly close. 
Temperature changes alone should squirm a string across a 
bridge with more minute but more frequent dimensional changes. 
I have no idea where the notion that strings don't render 
through bridge pins came from, short of the unified rustoid 
string-n-pin, but it's very common, and awfully hard to shake.

As I said, I think it's possible that seating a string could 
trigger it's rendering through the bridge. I don't think 
that's an unreasonable possibility, but I don't believe that's 
the cause of the typical measurable pitch drop from seating. 
If it was, they should be going sharp once in a while as well, 
and that doesn't happen.
Ron N