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I'm curious about the mechanism of a guitar producing sound. Of course, I know once a string is plucked it vibrates in a superposition of several harmonics, but what I don't know is what happens next. The string vibrates, creating a pressure wave around it with the same frequencies as the ones it's vibrating with, these waves go into the sound hole, and then what?

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The string vibrates, creating a pressure wave around it with the same frequencies as the ones it's vibrating with, these waves go into the sound hole, and then what?

That's not correct. The string is too narrow to displace all that air. The string vibrates, and this string being coupled to the guitar's body, makes the body vibrate. This vibration gets transferred to the air inside and outside, and that's where the resonant harmonics of the body comes to play. The sound you hear is a combination of the small sound of the string pluck, plus the amplified sound of air in contact with the body.

If you think in terms of energy, the only input energy that goes into the system is the pluck you give. Without the guitar body, the string vibrates longer and dissipates energy through air slowly, making the sound and heat. But with the guitar body attached, the energy dissipates much faster because you have a guitar body and a whole lot more air vibrating. More air means better coupling with the atmosphere, and a louder sound detected by your ears. The trade-off for loudness is the duration of the sound, so energy is conserved.

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    $\begingroup$ Great answer! A friend once asked if the shape of a guitar body could alter the sound. I assumed it did thinking the air on the inside would favor some wavelengths over others, analogous to an asymmetric black body. This suggests the air inside has very little to do with the sound. $\endgroup$
    – R. Romero
    Commented May 17 at 17:02
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    $\begingroup$ Doesn't the guitar body also radiate some sound outward (especially the top/soundboard)? $\endgroup$
    – gidds
    Commented May 17 at 23:12
  • $\begingroup$ The surface of the guitar body also radiates sound. You can make an acoustic guitar without a sound hole, and it will make quite a bit of sound. $\endgroup$
    – Edward
    Commented May 18 at 1:04
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    $\begingroup$ @gidds Oh yeah, more sound comes from the top and the body than comes out through the sound hole. The hole is more like a port in a subwoofer - it helps to tune the lowest resonances. Sound does come out of the sound hole, but covering the sound hole with a rubber disc (to reduce acoustic feedback in amplified situations) doesn't make a guitar much quieter at all. $\endgroup$ Commented May 18 at 4:01
  • $\begingroup$ @ToddWilcox That makes sense. I've updated the answer, thanks for sharing! $\endgroup$
    – AlphaLife
    Commented May 18 at 6:00
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the sound you hear is determined by the frequency of the vibrating string, but the string itself does not move the air significantly enough to create sound waves, the body of the guitar amplifies it so you can hear it. after it reaches your ear, your ear produces electrical signals that your brain interprets as “sound”.

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Prior answers are basically correct, but remember the builder. He decides on the sizing, shape, timber properties, glue which does not dampen sound etc, and many other components, all of which effect the final result as in sound power and quality and harmonics. Electric guitars basically use the pickup/transponder to make the sound, but still the string and guitar give an original quality which can be modified.

The sound energy is transmitted to the body of the guitar via the sound bridge where the strings terminate on a board that is glued to the face of the sound cavity.

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