Why not call the phenomenon what it is (as you have all clarified): a pressure wave.
I believe that they call it a sound wave due to the fact that there are at least three waves that are roughly the same distance apart, traveling at the same speed. So if you greatly sped up time, the passage of these waves would be analogous to sound waves in our atmosphere.
"Sound," "acoustics" and such terms make no sense without an observer,
I would say that in the physical sense, sound and acoustics still make sense even with no one around to hear them. In the case of acoustics, sound waves generated by a remotely controlled device in a room still interfere constructively and destructively depending upon various factors even without there being an observer within 50 miles.
If a tree falls in the forest and there is no one there to hear it, does the tree exist?
I guess that my point is that it depends upon how one defines sound. If, philosophically, one insists upon there being an observer, then there is no sound when a tree falls in the forest if no one is there to hear it. (The tree's existence has nothing to do with there being an observer). :-) However, if one abstracts one's self from such ideas, one can see that there are still sound waves, and thus sound, generated when the tree falls. Greg T. PS a fun fact: This reported "sound" Has a frequency of around. 1.596*10^-15 Hz. That is to say, the time between the passage of one wave and the next is roughly 19,854,825 years.
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