[Flysher]

Obviously there must be air molecules to transmit soundwaves, but the speed is not really dependent on density. For sound waves to propagate, air molecules must bump into each other, so the wave can travel from molecule to molecule. If it is warm, all the air molecules are in motion and bump into each other more. The colder it gets, the less they move around and bump into their neighbors. This slows down how fast the sound wave can travel.

I never knew how that worked, thanks for that.