Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Guitar string tension: effect of total length

Tags:
  1. Dec 3, 2014 #1

    sgb

    User Avatar

    I suspect my question will be somewhat unique, please forgive me if it's entirely out of place. (Please also forgive my ignorance when it shows, my knowledge of physics is extremely limited.) You might wonder why I'm asking it here, rather than on a guitar forum. Let me simply say that the guitar community is infused with all manner of voodoo-like beliefs, such that it can be difficult to arrive at a straight answer on such matters. I don't expect that to be a problem here.

    I'm interested to learn if the total length of a guitar string should, in theory, have any effect on its tension, i.e., it's bendability. Specifically, my question relates to headstock design. For those unfamiliar with guitars, let me quickly explain a few things.

    A guitar string vibrates between two points: (1) the bridge, at the picking end; (2) the nut, at the other end.

    The headstock is the material beyond the nut, where the strings are tightened by being wound around tuning pegs. (The strings are anchored at the other end, beyond the bridge.)

    Headstocks generally come in two forms: (1) three tuning pegs on each side, called "3+3"; (2) all six pegs on one side, called "in-line."

    In-line headstocks themselves come in two forms: (1) standard form, where the tuning pegs are on top, such that the thicker, lower-pitch strings have the least amount of length beyond the nut, since those tuning pegs are closer to the nut; (2) reverse form, where the tuning pegs are on bottom, such that the thinner, higher-pitch strings have the least amount of length beyond the nut.

    And now I finally get to my question: Is there any theoretical reason to expect that the amount of string beyond the nut will have any effect on the tension (expressed as bendability) of the string between the nut and the bridge?

    If the choice of standard or reverse in-line headstock should in theory have such an effect, I suspect most guitarists would choose the form which would impart greater bendability to the thinner strings and lesser bendability to the thicker ones.

    I'd like to know if there's any theoretical reason to expect such an effect, even if in practice it would be too little to expect most players to feel a difference on a typical guitar. Should there be such an effect, palpable to the player, on a ridiculously atypical guitar? Suppose, for example, that the headstock is one meter long, such that there is even more string beyond the nut than between the nut and bridge. Or, for a visual unrelated to guitar, suppose a length of rope, pulled taught across two logs by two persons, such that it could be "plucked" between the logs; should the distance of the persons from the logs, and thus the length of the rope beyond the logs, have any effect on the perceived tension of the rope between the logs?

    In order to raise a string of a given gauge to a desired musical pitch, it must be placed under a certain amount of tension. Some guitarists believe that the placement of the bridge and nut along the length of the string will have no effect on its bendability. Others believe that it will, and that the headstock form is therefore relevant.

    So, should the total length of a guitar string (or any other wire, cable or rope, for that matter) have any effect on its perceived tension between the terminal points of its vibration?
     
  2. jcsd
  3. Dec 3, 2014 #2

    Danger

    User Avatar
    Gold Member

    That's a really good question, and well presented. I don't know the answer. Among many reasons, one is that I don't know what effect the bridge has on vibrational nodes. Logic tells me that vibrations should be almost entirely damped out when they hit it, but that obviously isn't the case or messing about with the strings on the neck with your other hand wouldn't do anything. The one thing that I think might be applicable is that a long string (I'm thinking on a large scale here, like a gondola cable or power line) takes a lot more force to be stretched to the same curvature than a short one does. I kinda think that such might be due to gravity rather than an intrinsic property of the string, though.
    Good luck with finding an answer from someone else who actually knows about this stuff. There are a lot of them around.
     
  4. Dec 3, 2014 #3

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    If the string past the nut is just danglin' in the breeze, it has no effect on the sound made by the taut portion of the string.

    The bridge and the nut are node points on the taut string, the points where no vibration takes place.

    This article discusses briefly the physics of string instruments:

    http://en.wikipedia.org/wiki/String_instrument

    The frequency at which a string vibrates depends on the length between nodes, the tension, and the linear density of the string (how much a string weighs for each unit length).

    High pitch strings are light and highly tensioned; low pitch strings are heavy and more loosely tensioned. In a guitar, for example, all of the strings are roughly the same length, but in a concert piano, there is much variation in the lengths of the strings, which in turn, influences the shape of the instrument.
     
  5. Dec 3, 2014 #4

    Danger

    User Avatar
    Gold Member

    I always wondered why they look like that. Thanks.
     
  6. Dec 3, 2014 #5

    sgb

    User Avatar

    But it isn't just danglin' in the breeze. The string is anchored somewhere behind the bridge (either at the back of the guitar, if it's a string-through-body design, or at the back of the bridge behind the saddle, which is the actual point where the vibrational length of the string begins), and past the nut at the tuning pegs. These points could in theory be any distance from each other; the scale of the guitar is determined by the distance between the bridge saddle and the nut. The string, however, is taught all along its entire length, and, presumably, under equal tension all along its length. Suppose a mile long string, with a standard guitar scale (let's split the difference of the most common scales and call it 25 inches). So we have a bridge and nut 25 inches from each other, with the strings passing over them, at slight angles to maintain pressure at those points. If the tension is constant along the length of the string, should it make any difference how much string there is beyond those points? (Let's eliminate gravity from consideration in the case of my ridiculous mile-long string.)
     
  7. Dec 3, 2014 #6

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    No it shouldn't. When you pluck the guitar string, the part which vibrates and makes the sound is the length between the nodal points, that is, the bridge and where the nut takes up the slack in the string.

    I think if you were to measure several different guitars, acoustic, electric, whatever, which are tuned to give the same chords, you'll find that each was made from similar gauge string and each has a similar distance between the bridge and the nut.

    If you know any sound engineers, I bet they would have equipment which could tell you at what frequency a given string vibrates when it is plucked. You could round up and test several different instruments, heck, even a 2x4 with some string nailed down on it, and see how the frequency of the sound changes with string length, with excess behind the bridge, the color of the instrument, whatever variables you want to investigate. This is how you learn about something, by making an actual test. The guys who just shoot the breeze will be disappointed, though, because some of their cherished theories may not survive a scientific test. The latter is just as bitter to realize in the musical world as it is in the scientific world.
     
  8. Dec 4, 2014 #7

    Bandit127

    User Avatar
    Gold Member

    Consider a Floyd Rose equipped guitar with clamps on the nut (a locking nut). When the clamps are done up you can cut the string between that and the tuning pegs on the headstock with no change in string tension.

    That suggests to me that any string length beyond the nut is irrelevant to string tension.
     
  9. Dec 4, 2014 #8

    Danger

    User Avatar
    Gold Member

    Oh, yeah! Bring on the jug band with the washtub bass! :D
     
  10. Dec 4, 2014 #9

    sgb

    User Avatar

    What you've said is correct, but it seems that I've failed to convey what I'm trying to determine. Let me try wording it another way.

    Suppose you have a 36-gauge (.036 inch) string. In one scenario, you fasten the string at two points exactly 25 inches apart, and tune it to 440 Hz. In another scenario, you fasten the string at two points 50 inches apart, but slide a bridge and nut under the string, 25 inches apart, and tune it to 440 Hz when plucked between those points. In each scenario, the string tension will presumably be the same. The question is whether the string will be more or less bendable in the second scenario.

    I should have stated this before, but the string is free to slide inside its slot in the nut. This is where some guitarists get the idea, which I'm hoping can be confirmed or denied by physics, that a greater or lesser amount of string beyond the nut should have an effect on its bendability. Complicating the issue even further is the lack of consensus on whether more or less string beyond the nut should impart greater bendability! On the one hand, some players believe that a standard in-line headstock should make the thinner strings more bendable, based on the idea that the extra string beyond the nut (on a standard in-line, the tuning pegs for the thinner strings are furthest from the nut) imparts greater elasticity and allows more slide inside the nut slot. On the other hand, some players believe the opposite, that a reverse in-line headstock, having more string beyond the nut for the thicker strings, will make those strings stiffer because of the longer total length!

    As you can see, these contradictory beliefs are in need of some solid physics to back up one side or the other, or to disprove the idea altogether and show that total length should have no effect on the bendability of the string between the bridge and nut.

    Indeed, a locking nut renders the whole discussion moot, but not all guitars use a locking nut. As I hope I've made clear, I do understand that the tension will be the same along the entire length of the string when tuned to pitch between the bridge and nut. The question, as I hope I've now clarified above, is whether more or less extra string beyond the nut will make a string more or less bendable, despite the fact that the tension is the same along the whole string no matter how much extra lies beyond the nut.
     
  11. Dec 4, 2014 #10

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    I'm afraid you've lost me when you talk about the 'bendability' of the string. I'm not a musician, so I'm not sure what phenomenon you are trying to describe. All I know is if the string is a certain length, a certain size and at a certain tension, when you pluck it, you should get a certain frequency of vibration. That's what physics tells you about how the string responds.
     
  12. Dec 4, 2014 #11

    Bandit127

    User Avatar
    Gold Member

    I am a guitarist and I do understand what happens when you bend a string. You increase the tension and therefore the frequency.

    However I do not understand "bendability" and I suspect it is entirely subjective anyway. The OP should define bendability in better terms for a physics answer.
     
  13. Dec 4, 2014 #12

    sgb

    User Avatar

    Agreed, "bendability" is a poor word, but I could think of no other. Let me try another visual.

    Imagine you're standing on the neck of a giant guitar. If you pull on a string, you will clearly see it sliding inside its slot in the nut. The question is whether the amount of string beyond the nut should have any impact on the ease of pulling the string. If the guitar had a locking nut (and if we eliminated any potential movement at the bridge saddles from the equation), then clearly all we'd be doing is stretching the string along its scale length. But with a standard nut, the string is also moving inside its slot, and is stretching along a greater total length. Should this alter the ease of pulling the string (its "bendability")?

    As I said before, I'd like to know the theoretical answer to this even if in practice it is unlikely to be felt by the player on a typical guitar. Suppose, if you like, a ridiculously long string beyond the nut; would it have any effect?

    Thanks everyone for staying with me so far.
     
  14. Dec 5, 2014 #13

    billy_joule

    User Avatar
    Science Advisor

    This is a basic experiment you can do on a lock nut equipped guitar. Bend with the lock not off, then again with it locked down, I think the effect is definitely noticeable.
    I found the extra string length would require a greater bend distance to reach a certain pitch.
    I concluded it was because you are not only increasing the tension in the vibrating length but also the nut-tuner distance.
    Look at your (non locking) nut while bending, you can see the string sliding through the nut while bending - The string is elastic and the nut-tuner length is undergoing extension.
    This effect is even more pronounce on certain jazz guitars where the tail peice is some distance from the bridge - One of my guitars (epiphone Joe Pass) has 23cm of non vibrating sting on the G & D strings that undergoes extension while bending.
     
  15. Dec 5, 2014 #14

    sgb

    User Avatar

    Interesting. So, is it your conclusion that the reverse in-line headstock is preferable to the standard in-line, if the player desires that the treble strings be more "bendable" and the bass strings be less so?

    Speaking of experiments, I have an idea for one. It requires: (1) a guitar with an in-line headstock; (2) a firearm trigger-pull scale.

    1. String the guitar with only two strings, of the same gauge, at the two outer positions (where the two E strings normally go), tuned to the same pitch.

    2. With the scale positioned at the center of a string (12th fret), pull it across the neck to the opposite edge and record the reading on the scale.

    3. Repeat with the other string.

    If the readings on the scale are different, then it does make a difference how much extra string lies beyond the nut.

    Unfortunately I have access to neither of the requirements for the experiment. Can anyone tell me if there is any theoretical reason why the readings for the two strings should or should not be different?
     
  16. Dec 5, 2014 #15
    To speak about "bendability" sounds like you are talking about the bending stiffnress (EI) for the strings. I think all of our theoretical models for vibrating strings assume infinite flexibility.

    Another problem with our models is that they assume infinite stiffness for the support structure. In reality, the guitar body and neck have finite stiffness, so the models do not fit in fine detail.
     
  17. Dec 12, 2014 #16

    jh0

    User Avatar

    I'm sorry to join in so late, but I think what "bendability" is. But in my opinion what is important for the guitarist when he's bending the string is to reach the note he wants to play. It is important to remark this, because in my opinion if there is a lot of string behind the nut (and/or the bridge), it will be easier to bend the string if we think in terms of distance, but the string tension will not rise so easily as with a locking nut or a shorter length of string behind the nut. I believe the effort and the deflection (in terms of length) of the string will be less with a locking nut.
    Let's assume the string is attached (locked) at both ends as in the following drawing.


    http://imageshack.com/a/img674/2648/QHpR67.png [Broken]
    In order to reach the desired note, the guitarist has to bend the string the distance d, so the string is deformed and tension is increased from T to T'. The force he exerts on the string is f.

    Now let's make the thought experiment proposed by sgb and think of a guitar with a distance between the tuners and the nut several times the scale length. If we pull the string sideways at the middle of the scale length we want the tension to increase accordingly, from initial tension T to the target tension T'. But as there is a lot of string length to stretch, we will have to deform it (increase its length) more and the string will travel a distance D, in order to reach the same tension T'.

    http://imageshack.com/a/img901/7676/1YQz61.png [Broken]

    As D>d, the angle between the two forces T' will be smaller, so the force F that the guitarist has to exert on the string will be considerably higher.
    So in this case it will be more difficult to reach the note, the guitarist has to bend further the string and he will need more force.

    In my opinion bending should be easier with guitars with locking nuts or with short "free" lengths of string behind the nut and saddle. But as these distances are comparatively small against the scale length the difference will not be much (at least with common guitar designs).
     
    Last edited by a moderator: May 7, 2017
  18. Mar 8, 2015 #17
    I've been really interested in this question for a few years now, and I'm glad I found this forum post!

    The reason I was wondering this is because Jimi Hendrix played a Stratocaster guitar strung backwards. Essentially this means that the strings that get bent more often in blues music (the high E, B and G strings) had LESS string length behind the nut.

    According to the ideas described by billy_joule and jh0, this would mean that it would be easier for him to bend the higher 3 strings than on a typical Stratocaster. This, along with the fact that he usually tuned a semitone lower than E standard, might have facilitated his incredible skill and nuance when playing his bluesy bent-note melodies.

    In order to gain some practical perspective on this subject, I ordered 2 (essentially) identical necks from warmoth.com. One with a standard headstock, and one with a reverse headstock. In a completely un-scientific study I did a month ago, I compared the "feel" of the two. Personally, I could not feel if the reverse headstock was more "bendable" on the high strings.

    In my opinion the difference in string length behind the nut may or may not have helped Jimi's bending, but the fact that he tuned to E flat standard definitely did. As far as my guitar playing is concerned, my conclusion is this: The marginal difference in performance does not outweigh the utter pain in the butt it is to string up and tune a guitar with a reversed headstock.
     
  19. Sep 17, 2015 #18
    Long story short, sgb, for a couple of years I have been studying some of the equations behind what you asking about, and yes, I believe quite firmly that it does.

    If you haven't already, I would recommend looking up the equations for string tension, as well as 'Modulus of Elasticity' and 'Poisson's Ratio'. I have been attempting to write an equation which would allow a person to know the distance they would have to bend any plain string across the same fret to result in the same bend interval, and from there, if they wish, narrow down which plain string gauges they will need soas to better 'set' that bending distance, thereby making it more predictable from string to string, and therefore the learning curve of the instrument that much more steep.

    (It would, of course, require a number of measurements of the guitar itself, such as scale length, distance from bridge/tremolo-block to tuner of each string, the string height of each at the 12th fret, the nut-tuner breakover angle of each, each string's diameter, etc.) As a side note, apparently D'Addario (if not also other string manufacturers) use wound strings with a hexagonal core, as the edges of the hexagon make it much each for the wrapping wire to 'bind' to the core wire, so by knowing the area of a hexagon... you could arguably calculate, and by extension better 'set', the bending distance of wound strings!

    I would also recommend reading about 'progressive tension'. D'Addario has 'balanced tension' string sets available (and the idea of 'balanced tension' had been out long before they chose to capitalize on it), but some folks felt their bass strings still sounded a little muddy, hence 'progressive tension' came about. (I've tried writing D'Addario about it, but they haven't received enough requests to make seem it worthwhile to them.)

    However, with progressive tension comes even MORE progressive friction (meaning progressively worse and worse tuning stability from string to string, which is why a person would be forced to wind more string around the string post (be it up or down). This could be accomplished a little bit easier using string posts whose heights are intentionally 'staggered', and going from there.
     
    Last edited: Sep 17, 2015
  20. Sep 19, 2015 #19

    Randy Beikmann

    User Avatar
    Gold Member

    I happened to have done a lot of research in this area, although it was on belt drives in cars. The physics of each is about the same.
    Only three things matters for the tuning of a guitar string 1) the amount of tension on the string, 2) the mass per unit length of the string, and 3) the length of the free span of the string. The reason for this is that the bending stiffness of the string is very low - the tension is what makes the string come back to center after you pluck it.
    As it vibrates, the string produces forces on the supports at both ends, perpendicular to the supports. These forces vibrate the sounding board of the guitar, which then acts like a speaker and produces the sound.
     
  21. Sep 22, 2015 #20

    JBA

    User Avatar

    I know nothing about this subject and before scanning through these posts, quantum physics was #1 on my list of complex subjects but now I think I'll drop it to a #3 or so.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook