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I had a recent issue with my high e string where the saddle was adjusted as short as possible but the twelfth fret was still very flat. I read online that a new set of strings may fix this, and that turned out to be a perfect solution. My question now is, from a physical standpoint, why does string age affect intonation? I can understand why old strings won't hold their tuning as long, but I don't understand how age can throw a strings intonation off.

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  • What was the string made of?
    – phoog
    Nov 17, 2021 at 16:07
  • Nickel I reckon. The strings were on the guitar when I bought it. Standard electric guitar strings.
    – Awalrod
    Nov 17, 2021 at 16:12
  • This is just a suspicion, so I won't put it as an answer yet: As strings age, they stretch. As they stretch, they become thinner. Note that the lighter gauge strings have the saddle set shorter than the heavier gauge strings of the same type, though some of that has to do with the height of the action.
    – Theodore
    Nov 17, 2021 at 16:18
  • I would claim age in itself does not cause any intonation change. Crud buildup from grubby or sweaty hands does. There's also the bizarre, yet as far I I'm aware untested pseudo-science that one person can kill strings in days while another can keep playing them forever without them going "bad". I used to know a guy who, if you lent him your guitar for an afternoon, within days the strings would need changing. I've known lesser versions of this across many players. Some of my guitars have 15-year-old strings & no intonation or tuning issues [I like mellow on some ;)
    – Tetsujin
    Nov 17, 2021 at 18:47
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    @Tetsujin Good point; aside from chemical corrosion, I wouldn't expect strings that don't get played on to go false just from age alone. But if it's true that the problem is from actual mechanical damage or deformity, then it makes sense that more "vigorous" technique might make them die sooner (though I don't know about "in an afternoon"!) Nov 17, 2021 at 18:50

3 Answers 3

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I've been curious about this too. I imagine this is the same phenomenon that violinists refer to as a string "going false." The effect is the location of pitches becomes inconsistent along the length of the string, especially noticeable on a fretless instrument; i.e. if you tried to play, on two strings, a pitch a perfect fourth higher than the open string, the placement would have to be slightly different on the two strings (which is of course impossible with frets). I've also noticed, especially with an unwound wire string like the violin's high E, that plucking a false string can produce "two pitches," as if an E and another slightly detuned E were being played at the same time.

This page simply says "A 'false' string is one with uneven thickness and mass along its length." It suggests that it involves the "flattening" of the round cross-section of the string. This discussion thread is rambly and largely speculative, but I imagine much of that speculation is true, that it also involves changes to the elasticity of the metal. The fact is, for a wound string, there are so many parts that there could be a lot of factors. The string's core is perhaps a number of braided steel wires, which could become inconsistent in thickness, shape, or elasticity, and the winding could become deformed or perhaps have its "coils" spread apart or together.

Of course, if the new strings hadn't solved the problems, there could be other suspects as well. The wood of fretboards wears grooves between the frets over time, and frets themselves could become worn and be inconsistent from one string to another.


I can understand why old strings won't hold their tuning as long...

Actually, I would expect (and find, in practice) the opposite. New strings always have a "break-in period" during which they stretch and have to be retuned regularly (the period varies in length and intensity depending on the material), but once they've "settled in," they generally hold their pitch quite well (unless maybe eventually some mechanical flaw like we've been discussing impacts their stability).

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tl,dr: Finger gunk.

It's the same reason why strings become dull over time. When playing. the oil, sweat and salt from your fingers interacts with the string and results in corrosion and accumulation.

This is more pronounced where you fret the most and this results in an uneven mass distribution and the center of gravity moves slightly away from the 12th fret. Hence it's out of intonation.

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    If you observe the 12th fret tone to be flat compared to the 0th flat, then the finger gunk theory would mean that more finger gunk accumulates in the upper half of the string than in the lower half. As the left hand contributes more finger gunk than the right hand does, this would suggest that a lot of the playing was happening above the octave (which would strike me as unusual playing style). So the outcome, a flat octave, would be a slightly unexpected consequence of finger gunk accumulation. Nov 19, 2021 at 7:02
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    The finger gunk theory is testable. Soak your strings in ethanol for 24 hours and see what happens with finger gunk gone. Nov 19, 2021 at 7:16
  • @JirkaHanika, I suspect the physics is much more complex. Presumably, the effect of finger gunk is to cause differentials in dampening and tension across the length of a single string. Those effects probably interact with string use, such that higher use + finger gunk impacts the string differently than lower use + finger gunk. Another element to consider is the cumulative effect of many spots where the strings are degraded. I feel like the math would need to be worked out to show that this would always produce flatness in every instance. Soaking in ethanol won't reverse permanent damage.
    – jdjazz
    Nov 20, 2021 at 18:04
  • @jdjazz - That's the point. Cleaning the string lets you separate wear effects from gunk effects. What will be the finding? I don't know. I do get your point about dampening versus weight. Perhaps not about tension though, tension has to be constant even on an unevenly gunky string. Nov 20, 2021 at 23:15
  • @JirkaHanika maybe I'm not familiar enough with the gunk theory. I thought it was proposing a mechanism that causes the wear on the strings. The physics is starting to go beyond my knowledge, but I thought the tension isn't constant (1) if the string has kinks, (2) if there's an applied force on the string (not really relevant in this scenario), (3) or if the string is accelerating different masses along the length. Without a ton of direct knowledge, I'd guess that the 3rd is most relevant here, since each bit of string is accelerating as it vibrates, and those bits can have different masses.
    – jdjazz
    Nov 20, 2021 at 23:29
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Probably the already given answers are also right, in the sense that the mentioned factor physically modify the harmonic response of the string. But I think soaking in ethanol for 24 hours will not make the string new, because of a physical phenomenon called "fatigue", that I guess plays the main role here.

As you know every material have his own elastic constant E (young modulus), in the case of steel it is around E=210 GPa. The fatigue is a phenomenon that ""make the material weaker"" when the same point of material is subjected repeatedly to many cycles of the same load. https://en.wikipedia.org/wiki/Fatigue_(material) You can see that e.g. the "main" LA string goes 440 Hz (around? sorry i'm just half musician), so it does 880 cycles from minimum tension to max every second that it vibrate. Every material have its own characteristic number of allowed cycles before suffering of fatigue (see Whaler function). From this number you can compute by simple division the number of seconds that the string can vibrate before suffering of fatigue. This phenomenon modify the value of this Young coefficient E (and also others like Poisson coeff., more complicated, just doesn't matter, but the idea is the same). But as you know the vibrating string doesn't have the same tension everywhere: every harmonic have his own wavelength. Assuming the string is vibrating sinusoidally, in a full period we have one max and one min points (the one with horizontal tangent line, i.e. derivative 0, for those who knows a bit of math) and those points will be the most strained ones. Instead, the nodes of the mode will be less strained ( this because the differential equation of the vibrating string is Yxx=k*Ytt where k basically is modified by tuning. xx and tt are partial derivations). https://en.wikipedia.org/wiki/Normal_mode To conclude, the string will fatigue not in a constant way, but differently in every point. If you add this to all imperfections (like that touching the string non uniformly will consume it non uniformly for example), after a while the string doesn't perform as new.

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