The guitar is an example of a plucked-string instrument. The vibrating string radiates very little sound. However, energy is transmitted to the body of the acoustic guitar. It is the resulting vibrations of the soundboard and the air inside the cavity that mostly contribute to the sound perceived by the listener.

The front and back of the guitar vibrate in modes just like the membrane.  The pictures below show holographic measurement of some of these guitar modes. By clicking on the pictures, you can see animations of some modes of vibration of the soundboard.

(Courtesy of Dr. B. Richardson, Cardiff University)

For more information on guitar acoustics, see

www.astro.cf.ac.uk/groups/acoucomp