A couple of interesting segments from the BBC ... one using schlierin photography to demonstrate the existence of shock waves in a trombone's output ... and the other a laser holographic technique to show the patterning of string acoustic instruments soundboards from the Acoustical society of America.

Schlierin images of trombone shockwaves

The implications for an audio system to be able to reproduce this are fairly alarming, also the capability of producing damage to the listener!

Holographic Interferometry images of string instruments.

These are beautiful images indicating the complexity of the sound production by stringed instruments and how it relates to the structural nuances.