If a tree falls...

[randolph]

Originally Posted by smc

That is exactly as I see it. If there is no creature whose organ of hearing is within the range of hearing, and if the mechanical wave that is nothing more than an oscillation of pressure transmitted through the air is not sufficiently strong, then it is ONLY a mechanical wave and not sound.

A disturbance in the air can be interpreted by the brain as some form of sound.
Some plants can also respond to vibrations. Tomato blossoms require vibrations to pollinate. Strawberry plants sense vibrations as insect attack and respond with chemicals to resist the attack. So living things can respond to vibrations.
A sound may be defined as a vibration detected by a brain and interpreted as a sound. Typically, a sound would have some meaning, roar of a lion or call of a bird for example.
A tree falling would create a vibration and possibly a screech if it fell on a rabbit, of course, something would have to "hear" the screech.