Big string bends on acoustic and staying in tune

[JeffreyAK]

Originally Posted by fazool

That's so weird though because if you put a piece of guitar string on a tensile tester, it won't stretch, then stop. Intuitively, I think its going to neck down and snap with very little transition period.

You certainly bring up a compelling thought with your observations.

Maybe it's a combination of the two. Your initial deformation happens once, then any instability after that is slack. Perhaps.

Could be time for another experiment! I'm not sure what that would look like, though. A good rainy day project.

[YeOldRocker]

The OP mentioned locking tuners, which has no real bearing on and does not solve your problem; locking tuners simply clamp the string in the thread hole, enabling simpler, faster string changes. To some extent, less wrapping around the post is needed, as the string will not pull out of the hole during installation and final tuning. My Strat has locking tuners and they're wonderful and can spoil you with their string-change ease, but they will not solve the problem of string slippage from slack left around the pole itself, although they do help a bit.

As others have pointed out, I think that the main issue here when bending (or strumming hard) is the string around the post still has some slack in the wrapping. When I play lead on electric, I bend strings a lot, with very little de-tuning. Same with acoustic, although I do bend far less and less extremely - half-steps, rather than the occasional whole steps, for eg.

Strings do wear out with bends as the strings are pushed over the frets sideways, and that will make them less tunable, eventually, but they will also start to sound old and dull by that time. I can't speak for the physics of strings actually stretching, but I suspect that is not happening in any obvious, measurable way. So, I still think that if your guitar is going wildly out of tune with a bend, then its the wrapping at the post, or uneven friction at the nut, that's slipping.

[robj144]

Originally Posted by JeffreyAK

Us physicists like to do experiments to get real data. So here is what I did out of curiosity, to see what happens to a brand new string when we "break it in" by stretching it out.

1) Marked two tiny black spots on a new Ernie Ball 0.010" string with a sharpie, placed so that they would wind up between the nut and saddle on my Strat when I mount up the string.
2) Measured the distance between the two spots as precisely as I could, which is approximately a tenth of a mm for changes and approximately 1 mm absolute accuracy, using a meter stick with two good metal rulers with 0.5 mm increments taped to it. The initial separation was 556 mm.
3) Removed my old E string and mounted the new one, being careful not to rub off the sharpie marks.
4) Tuned the string to E, 329.6 Hz.
5) Stretched the string vigorously with my fingers. I noted that the tuning dropped a half-step to Eflat, 311.1 Hz.
6) Retuned to E and stretched again. The tuning dropped a little bit.
7) Retuned to E and stretched again. The tuning did not drop.
8) Removed the string carefully and remounted it on my measurement device. The final separation was..... 556 + 0.1 mm.

So any real deformation of the string was at the limit of my ability to measure, and approximately 0.018%. This compares with the change in frequency due to stretching (5.6% after the first stretching routine), and the required decrease in mass per unit length required to explain that frequency change (twice that, if I did the math right).

Conclusion: A string can indeed stretch and deform a bit, but what I measured can't possibly account for the full half-step drop in tuning I heard. In fact it's nowhere close.

So what is changing? It seems unlikely to be the tuning peg, since the string was wrapped nicely and tightly. My guess, it's at the ball end somewhere, but that's a guess.

If a string doesn't deform when it's brand new and just installed, it certainly won't when you bend it up a half step or two. But it's conceivable that whatever is slipping when you break in a brand new string, could slip a bit more when you bend it up, particularly if it's still relatively new and if you haven't gone through a stretching routine to get it to hold a stable tuning.

Just to point out... if the only quantity which is changing is length (and thus mass per unit length to conserve volume), the change in length goes as the square of the ratio of frequencies. To change according to your measurements, requires about a 13% change in the length of the string. So that's not what is happening here. Clearly the tension is changing as well.

[Orfeas]

New strings might go out of tune a bit.

[ljguitar]

Hi Jimmy R

I do a lot of bends on acoustic, and as a result, no matter how 'settled' the strings are, I tweak once in a while mid-song when the bent string goes flat.

Acoustic bends have more of an effect on my strings than when I bend on my electric guitars (and I bend strings a lot on both).

[JeffreyAK]

Originally Posted by robj144

Just to point out... if the only quantity which is changing is length (and thus mass per unit length to conserve volume), the change in length goes as the square of the ratio of frequencies. To change according to your measurements, requires about a 13% change in the length of the string. So that's not what is happening here. Clearly the tension is changing as well.

Length is the same, though, between nut and saddle. If the string was deforming inelastically in response to "break-in", mass/unit length could change, and perhaps it does a tiny bit, but you're right, it's nowhere near the amount required (12.x%) to explain the tuning difference from E to Eflat. Once I tune it back to E, the tension is the same as long as the length and mass/unit length do not change.

I admit, I am a bit puzzled as to what is really happening during "break-in". Could be several things combining. But, of course, it's real, and as we all know, if you don't deliberately "stretch" a new string after you install it, it will take a long time and a lot of playing before the tuning stops drooping flat.