Sound

[Leody]

To me it's clear that the definition makes the distinction that it does not need to be heard.

Nowhere does it say that it has to be heard in either the Mariam Webster's or Oxford English Dictionaries. They both clearly state that the wave vibrations within a medium are sound, which creates the potential for hearing. The sound is the waves, they create hearing when they hit an eardrum. Just because they don't hit an eardrum, doesn't mean they're not sound. They are still sound even when not heard.

[Dejan]

My mate looked it up in his oxford dictionary and it said what I already showed you before.
I just looked it up in my dutch dictionary. It says this:(i know u wouldnt understand, but you could translate it with google).

ge·luid het; o -en trillende beweging vd lucht die door het gehoororgaan wordt waargenomen

which means:

Sound: the vibrating from air that is caught by the hearorgan.(not sure if hear organ is a correct english word.. but you could also read it as a eardrum)

And about the mariam webster(or whoever she is)..

According to Merriam-Webster, sound is the sensation perceived by the sense of hearing. So that means that vibrating air is just that, mechanical vibrations of air molecules. When those vibrations are perceived by the sense of hearing, then they become a sensation; the sensation of sound. That is why we have an auditory cortex in the neocortex of the brain that interprets those vibrations as a tree falling, a bird singing, or the wind whistling through the leaves.
Here is an example: If you never heard a tree fall as it crashed to the ground and you were standing in the woods blindfolded as one fell, you would hear noise. The noise would be the vibrations in the air of the tree hitting the ground. Most likely you would hear something, but you would not know what it was. But, if you had heard enough similar noises before, your brain would then be able to identify the vibrations as being produced by a tree falling. Then it would be a sound.
So, going by the Merriam-Webster definition, the tree would make air molecules vibrate, but would not make a 'sound' if it fell in the woods and nobody was there to hear it.

I just realized that i was drunk yesterday when i made this topic, but it was a good discussion anyway

[Gunner Down Under]

I'll stick to my point before- all because the vibration doesn't reach your ear doesn't mean its not there.