I'm interested to know why the speed of sound is directly related to air temperature.
Molecules bounce around because they're hot, or rather, temperature is determined by how much the molecules bounce around. The greater the average velocity, the hotter the temperature.
When you increase the energy of a molecule by emitting a sound, it will carry that extra energy to other molecules as it bounces from one to another. It can only carry that energy to another molecule at the speed it's moving in the same way giving a letter to the postman will only get to the office as fast as he's driving. And that's only if he takes the direct route, which he won't.
So temperature is a mere stand-in for the average molecular velocity.
Density and pressure do affect the speed of sound in solids, but don't in gases, because an increase in pressure results in decrease in density, so they cancel out.