I know that tuners are one of the features that distinguish a classical guitar from an acoustic one.

But why are the tuners the way they are?

And are they still this way in this day and age because they just work or because they're perfect for their purpose?

EDIT: I meant the tuning pegs.

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    Do you mean "tuners", which are a tool for determining if an instrument is at the correct pitch, or "tuning pegs", which are the knobs at the end of the guitar to tighten or loosen the strings?
    – Aaron
    Commented Jan 14, 2021 at 3:02
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    'Machine heads' is more accurate.
    – Tim
    Commented Jan 14, 2021 at 8:40
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    @Edward: I'm not a friend of google hits as indication for correctness. At least Collins dictionary supports the claim under American English section giving as definition: a person or thing that tunes.
    – guidot
    Commented Jan 14, 2021 at 10:03
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    @guidot which is literally the function that the tuning pegs perform :)
    – Džuris
    Commented Jan 14, 2021 at 15:21

3 Answers 3


When what we think of as the classical guitar was normalized, it was just after luthiers switched from friction pegs like you would see on violins to the geared open-backed pegs, which were the advanced cool new tech at the time. They hit an optimized form early, and couldn't make it better without making an large departure, like steel strings with higher tension, so the guitars that get made are made to be the best and prettiest versions of that.

You can find acoustic guitars with that kind of in-line open-back tuner. I think I own four. But the closed-back style you often see are lubricated for smooth operation. I would guess the post is made from higher-quality metal to keep from being bent from the higher tension, but that's just a guess. There are also locking tuners, but I normally see them on electric guitars with whammy bars, not steel-string acoustics.

I could imagine classical guitars with the more modern tuner styles, as I have seen violins with geared guitar-style tuners and with geared tuners built to look like friction pegs, but musicians often go with their eyes not their ears, and would be likely to avoid guitars that don't look like the ones their heroes played.

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    Nice answer Dave +1, I’m wondering if the OP isn’t also referring to slotted headstocks on classical guitars as well... Commented Jan 14, 2021 at 6:16
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    Yeah, I'm thinking it's the slotted horizontal vs electric guitar-style vertical that the OP is asking about.
    – Tetsujin
    Commented Jan 14, 2021 at 10:48
  • I have both types of guitars, an old one from Madrid with violin style pegs (pain to tune) and one with machine heads.
    – user50691
    Commented Jan 14, 2021 at 12:37
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    Thinking of adding: some say that headstock mass does a lot for acoustic guitar sustain and tone, and choose tuning pegs to fit. I think I hear that most in bluegrass context, but that's the place where high performance is most valued in acoustic music. Commented Jan 14, 2021 at 20:43
  • And yeah, @ggcg, I own violins and they're a pain even with fine tuners Commented Jan 14, 2021 at 20:44

It's because the strings are different.

If you look at the shafts that strings are wrapped around, on classical guitar they are plastic and have much larger diameter than on acoustic. Nylon strings have lower tension than steel ones, and stretch much, much more when pulled into tension. The shaft has to be larger so that more string can be wrapped around it, and plastic, because metal would be heavier and nylon strings don't cut into the tuner like steel ones. It would be possible to build a non-slotted headstock with tuning posts with similar dimensions, but it would look ridiculous, and because of the huge number of string wraps, string break angle at nut would be inconsistent.

In other direction, acoustic and electric guitars with slotted headstocks do exist. The tuning shafts are steel instead of plastic and the gear ratio is typically lower than on classical guitars. They are uncommon because the slotted design makes string changes a huge hassle and the design doesn't have that many benefits.

  • Depends on the quality and expense of the tuner. The shaft is metal (seeing brass in the catalogs) but there's a roller around it, and that could be plastic or ebony or powder-coated aluminum. Commented Jan 14, 2021 at 20:51

The main reason is that nylon strings need to be stretched much more than metal strings to raise the pitch by the same amount. For this reason classical guitars need thicker pegs with larger circumference, allowing to reach the desired pitch faster, with less rotations. Metal string guitars need thinner pegs for better control of the pitch while tuning.

Some other differences might be historical, but there also could be some other technical or musical reasons. I don't know.

The tuners technology is being developed e.g. you can find classical guitar tuners with bearings where the pegs rotate in the holes, and with other improvements.

  • To be exact, they need to be tightened to greater tension ( not just "stretched more" ) Commented Jan 14, 2021 at 15:45
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    @CarlWitthoft They need to be stretched more, meaning, you need to elongate nylon string more to increase its pitch. Compare how much the pitch changes when you bend a nylon and a metal string by the same distance, e.g. 1 cm. Pitch of a metal string will increase much more. Also, in most cases tension of nylon strings is significantly lower than that of metal strings. Commented Jan 14, 2021 at 16:07
  • Elongating and greater tension are the same because of Hooke's Law, i.e. distance of excess string is proportional to tension. So you're both correct.
    – awe lotta
    Commented Jan 14, 2021 at 16:28
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    Nope. Nylon strings have lower spring constant and density, so they have lower tension for the same frequency and more elongation for same tension. The difference in spring constant is larger.
    – ojs
    Commented Jan 14, 2021 at 20:14
  • @ojs is right. Young's modulus for nylon is like 100 times smaller than for steel. So while Hooke's law obviously does apply, there are other, larger effects involved. Commented Jan 15, 2021 at 0:21

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