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This is a question about the frequencies that remain on the string during the decay of vibrations. As I understand it decay occurs because of the:

a- Internal damping of the string. This is due to the friction between material that make up the string).

b- External damping. This is due to vibrations that are absorbed by air.

c- Damping by the guitar body. This is the useful work. Vibrations that are transfered to the top.

Rate at which "c" occurs depends on the impedance matching between the string and the guitar body. My questions concern "c":

1- Does "c" get partly reversed by the elasticity of the top. Ie. are some frequencies returned to the string or even got canceled by the vibrating body depending on the phase of the returned vibrations?

2- Since impedance depends on the frequency, do some frequencies on the string get dampened faster than others?

3- What other factor would determine what frequencies present on the string during the decay?

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  • $\begingroup$ You might mention that (b) is a fancy way of saying that the guitar makes sound (i.e., it radiates acoustic energy) $\endgroup$
    – Solomon Slow
    Commented Jul 17, 2018 at 19:44
  • $\begingroup$ Guitars are designed so that the strings are impedence matched to the body through the bridge (ideally for all frequencies). Something that can happen when you have an amplified acoustic guitar is that the speaker drives the body at resonance which drives the strings with a possible phase shift from their original vibration. $\endgroup$
    – Ryan Thorngren
    Commented Jul 17, 2018 at 20:28
  • $\begingroup$ I think c is really the cause of "sound" being created or at least closer to it. The string pumps the body, the body pumps the air, and to some degree feeds back to the string, $\endgroup$
    – user196418
    Commented Jul 18, 2018 at 17:59
  • $\begingroup$ By (b) I meant strings' direct interaction with air. So (b) doesn't really produce audible sound. (c) is the actual acoustical amplification. $\endgroup$
    – Atilla
    Commented Jul 18, 2018 at 20:46

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yes to 1, 2, and 3.

if the string frequency is close to a body resonance, energy gets fed back and forth between the string and the body.

the treble frequencies generally get damped faster than the bass frequencies do.

other factors determining which frequencies reside on the string are 1) whether the string was plucked with a stiff object or strummed with a soft one (hard pick strokes excite a set of higher harmonics, soft strumming does not) and 2) how fresh the strings are (old strings have more internal friction which attenuates the high frequencies before they have a chance to get radiated).

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