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The Inner Workings of Guitars

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History of the acoustic guitar
The guitar origins are in Babylonia and dated back to 1850 B.C as clay plaques were dug up of people playing musical instruments which resembled the modern acoustic guitars showing distinct bodies and necks. Later evidence was found in Ancient Egypt that indicated instruments with marked frets along the neck of a primitive guitar.
How the sound is made:
If you put your finger gently on a loudspeaker you will feel it vibrate - if it is playing a low note loudly you can see it moving. When it moves forwards, it compresses the air next to it, which raises its pressure. Some of this air flows outwards, compressing the next layer of air. The disturbance in the air spreads out as a travelling sound wave. Ultimately this sound wave causes a very tiny vibration in your eardrum - but that's another story.

At any point in the air near the source of sound, the molecules are moving backwards and forwards, and the air pressure varies up and down by very small amounts. The number of vibrations per second is called the frequency which is measured in cycles per second or Hertz (Hz). The pitch of a note is almost entirely determined by the frequency: high frequency for high pitch and low for low .

Page Two: Jayden Foura
The strings
The pitch of a vibrating string depends on mass of the string, tension and the length of the string: strings with more mass vibrate more slowly. On steel string guitars, the strings get thicker from high to low. Tension is varied by using the tuning pegs: tighter gives higher pitch. Similarly, shorter string gives higher pitch. The sound produced by the string is faint which is then amplified by it...

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...ibrates a little almost like the air in a bottle when you blow across the open lid section of the top. In fact if you sing a note somewhere at F#2 while holding your ear close to the sound hole of the guitar, you will hear the air in the body resonating. This is called the Helmholtz resonance. Another way to hear the effect of this resonance is to play the open (A) string and, while it is vibrating, move a piece of cardboard back and forth across it. This stops the resonance (or shifts it to a lower frequency) and you will notice the loss of bass response when you listen to the sound hole. The air inside is also coupled effectively to the lowest resonance of the top plate.
The Helmholtz resonance of a guitar is due to the air at the sound hole oscillating, driven by the springiness of the air inside the body. This is analysed quantitatively in Helmholtz Resonance.
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