Talk:Guitar/Harmonics
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how do the notes in harmonics on frets 5,7, and 12 get lower sounds, yet theyare going up the neck, which usually has a higher sound?
- When you pluck a guitar string it oscillates, but not as a pure, single-frequency sine wave (as the picture might lead you to believe). Rather, we get the fundamental, plus all its harmonics (i.e., double frequency, triple frequency, quadruple frequency, etc). I hope this doesn't cause confusion, but in physics, the word harmonic is used to indicate the relationship between frequencies. So when I say "harmonic" here, I'm not talking about the technique described on this page, but rather, I'm talking about frequencies.
- Back to plucking an open string. Suppose we pluck the A string. If the guitar is tuned so that A is 440 Hz, plucking the A string will generate 440Hz, 880Hz, 1320Hz, 1760 Hz, etc. Each of these are the harmonics of 440 Hz (i.e., 1x440, 2x440, 3x440, 4x440, etc). Each frequency will be at a different loudness though (generally each harmonic is a bit quieter than the one that came before). This combination of frequencies is what gives any instrument its tone.
- Now suppose you touch the string over the 12th fret and pluck it. None of the odd-numbered harmonics can be made. It knocks out the 440 and 1320Hz components, because the "touched" portion of the string has to move for these sounds to be created, only it can't because your finger was in the way and dampened it out. However, the even harmonics can still be made, because the center of the string doesn't need to move to make those frequencies. Said differently, you will cancel out all the harmonics that are not a multiple of two. It might help to look at the picture again:
- See how the middle of the string isn't moving in the lower picture? When you move to a different fret, you will cancel a different set of harmonics. If you touch the string one third of the way from the nut to the bridge, it's exactly the same as if you touch the string one third of the way from the bridge to the nut. In either case you will cancel out the fundamental plus all the harmonics that are not divisible by three. Touch it a quarter of the way to the nut or the tail, and you cancel out all the harmonics that are not multiples of 4. Since there are fewer harmonics that are divisible by 4 than there are that are divisible by two, touching the string there will be quieter (you've dampened out more of the harmonics).
- If you touch the string at a distance one fifth from the nut (or two fifths, or three fifths, or four fifths), you cancel everything that is not a multiple of five.
