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Why when we play a guitar string it always vibrate in the fundamental harmonic?

  1. Sep 18, 2011 #1
    We have many harmonics in a string

    [PLAIN]http://img43.imageshack.us/img43/3452/dfshfghdfh.jpg [Broken]


    Why when we play a guitar string with the finger it vibrate in n=1, where L = lambda/2

    Even when we press the string in a given position (to make another note for example) the remaning L vibrates in the fundamental harmonic .

    Why we always have this and how can we play the second harmonic, or any other harmonic in a string?
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 18, 2011 #2
    Re: Why when we play a guitar string it always vibrate in the fundamental harmonic

    Good evening jaumzaum

    The fundamental is the lowest energy configuration. That is it takes less energy input to cause vibration in the fundamental than any other mode.

    It is an underlying principle of nature that systems try to adopt the configuration of least energy before entering higher energy states.

    So even if you get the string vibrating in a higher mode by overdriving (adding excess energy) some, probably a greater part, will be transferred to the fundamental.

    However there are always harmonics present, the note (vibration) is never purely at the fundamental.

    go well
     
  4. Sep 18, 2011 #3
    Re: Why when we play a guitar string it always vibrate in the fundamental harmonic

    What's the explanation for this? I'm "intuitively" thinking of the Boltzmann factor but I'm not sure if the canonical ensemble can be applied to a guitar string.
     
  5. Sep 18, 2011 #4
    Re: Why when we play a guitar string it always vibrate in the fundamental harmonic

    Hello again Mr Vodka, good luck with your second (?) year.

    Yes this principle appears in many places and guises, from thermodynamics to Occams Razor to quantum theory to structural mechanics.....to.... and the statistics of partitioning of states follows it.
     
  6. Sep 18, 2011 #5

    olivermsun

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    Re: Why when we play a guitar string it always vibrate in the fundamental harmonic

    There's pretty good evidence that other modes exist in the vibration, because a plucked guitar string doesn't sound like, say, a flute.
     
  7. Sep 18, 2011 #6

    rcgldr

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    Re: Why when we play a guitar string it always vibrate in the fundamental harmonic

    If you attached an oscillator to a string and it vibrated at non-harmonic frequencies you'd end up with moving waves, similar to jerking a taught slinky, rope, or hose up and down. This also happens just after plucking a string depending on where and how a string is plucked, but those non-harmonic moving waves are quickly dampened out.
     
  8. Sep 18, 2011 #7

    Ken G

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    Re: Why when we play a guitar string it always vibrate in the fundamental harmonic

    The answer is that you have totake the shape you give the string when you pluck it, and decompose that into elementary excitations of the various harmonics. Typically when you do that, you get a large component of the fundamental, say with the standard "triangular" pluck (look up Fourier transforms for more on this). If you want to play a pure overtone, you need to deform the string initially into a shape that looks like the overtone you want. That's more or less what you do when you move your fingers down the frets-- remember that the fundamental of a shorter string looks a lot like a harmonic of a longer one.
     
  9. Sep 18, 2011 #8
  10. Sep 19, 2011 #9
    Re: Why when we play a guitar string it always vibrate in the fundamental harmonic

    There must be more to it than node position, since a tapped or finger-damped harmonic has a clear piercing pitch even when the node position is the same as where you would fret the guitar and play normally - i.e. a "harmonic" sound at the octave fret is not the same as a fretted sound at the octave fret. Perhaps the guitar neck plays a role somehow. As the article states, you can get a really high, clear piercing pitch with a pinch harmonic, which basically puts the node farther up closer to the bridge.
     
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