[CAUT] pre-stretching new string?

[Fred Sturm]

Hi Ron,
    "Measurable" is not a precise word. Depends what your level of accuracy
is. + or - what? Under what circumstances?
    The experience I refer to isn't just noticing how strings go flat over
time. It's also knowledge of how materials behave. Most processes like
string stretching (deformation under load, if you like) happen in a
parabolic curve, with more rapid change at the beginning, and more gradual
change approaching and never quite reaching a limit over a longer time. I
have trouble with the notion that piano wire is different. How rapid at the
beginning and how gradual later? The more the process is "front-loaded," the
more impression one might get that "it all happens instantly" and it could
be "true enough for most applications" but still not absolutely true.  I
first heard that "piano wire doesn't stretch" (more or less what you quoted)
over 25 years ago. I've been keeping that in mind as the "official
scientific opinion" ever since. But I haven't been able to digest it yet.
    My take is that some of the pitch drop could be in the coils, some could
be in wood crushing, some in "conforming to bearing points," and some could
be in string stretching. I don't think any of us has full evidence to say
how much or little results from which. Most if not all of us rely on
anecdotal evidence, based on our own personal interpretation of the results
arising from our own pet procedures. We're probably all right and all wrong
to some extent. I do know that new strings drop in pitch over time on old
instruments with zero to negative bearing, in my experience (meaning wood
crushing probably wasn't a significant factor there).
    About suspension bridges, well, John Delacour's response stole my
thunder (though I knew nothing of monsieur Vicat). But in general, I'd say
(1) suspension bridges are engineered with considerable "forgiveness" to
allow for temperature related expansion and contraction as well a wind and
weight of traffic, and (2) piano wire is probably the use of steel involving
the highest tension over the longest period of time. Piano wire (and its
use) being a special case, it might not fall within the realm of standard
material experiments. And the amount of deformation required for a very
significant pitch drop might be very insignificant for an other use of
steel. Might not sag your suspension bridge enough to notice, for instance,
at least not enough to catch that mast as it sails by <G>.
    That, at any rate is my reasoning. I remain a skeptic, aware of the
various opinions and "truths" circulating around, but not entirely convinced
by any of them.
Regards,
Fred Sturm
University of New Mexico


On 6/6/07 5:38 AM, "Ron Nossaman" <rnossaman at cox.net> wrote:

> 
>> Hi Ron,
>>     I dunno. Those phrases "appreciable change in dimensions" and "no
>> practical significance" might be loaded (along with "measurable
>> proportions": who's measuring, and to what accuracy?).
> 
> "Measurable proportions" is a significant indicator.
> 
> 
>> Could be "not
>> significant in 99% of all applications, but there's enough creep to cause
>> 100 cents of pitch drop in piano strings over the course of a year, and
>> another 100 cents over the next 20."
> 
> What indication, measured by what and by whom, do you have
> that creep is the cause of this, other than wood compaction,
> as I've said, and coils settling, as Ed pointed out?
> 
> 
>> Just the skeptic in me, and, possibly,
>> years of experience. Of course, I could be wrong, and I could be
>> misinterpreting my "years of experience."
> 
> I think you are, along with most everyone else. Most people
> seem to think that music wire keeps stretching forever, but I
> don't think that's the case. Do they go out every year and
> tighten the cables of suspension bridges every year to pull
> the roadway back up level? Anyone know?
> 
> 
>> But it sure would be nice to tie
>> down one of these people who write this kind of stuff and ask some very
>> precise questions.
>> Regards,
>> Fred Sturm
> 
> Been looking for real information for years, on a lot of
> things like this.
> 
> Ron N
>