Why and how is sound produced when two objects hit each other?

When two objects collide and undergo a partially inelastic collision (so every one we experience in every-day life), they rebound to a certain degree, but kinetic energy is not conserved. Thus, the energy of motion must be converted to another type of energy. Thus, when two object collide, the most common forms of energy that kinetic energy is converted to are sound energy and thermal energy.

Some collisions are louder than others just because they cause a bigger local variation of pressure (which then propagates through air until finally gets heard). So, why some objects, even if the velocity before and after the collision seems to be the same, are louder than others? I mean, how do the different material properties enter in the phenomenon?

How and why, by means of solid and fluid mechanics or with an heuristical microscopical reasoning, can this process be explained?

-
There is no difference to how sound is produced in this situation and any other. See physics.stackexchange.com/questions/31469/… for general discussion. In fact, I think its just a duplicate of that question. – DJBunk Jul 14 '12 at 3:57
So, some collisions are louder than others just because they cause a bigger local variation of pressure (which then propagates through air until finally gets heard). Right? So, why some objects, even if the velocity before and after the collision seems to be the same, are louder than others? I mean, how do the different material properties enter in the phenomenon? – usumdelphini Jul 14 '12 at 4:03
Many comments deleted. I note that the most prolific participants both claimed to have an answer to the question, but that neither one wrote an answer. – dmckee Jul 15 '12 at 21:44

 A very interesting video showing physically based sound simulations: archive.org/details/Synthesi2001 The paper describing the simulation can be found at cs.berkeley.edu/~job/Papers/obrien-2001-SSP.pdf – mmc Jul 16 '12 at 3:39 Thanks for the answer. So, when two stones hit each other and they are in my hands, each one make the other vibrate by means of the impulse given and this vibration is trasmitted to the surrounding air to produce an audible wave pressure? I mean, can I neglect the detailed "solid" effects and just consider every collision as a source of vibration of the objects (even if the vibration is partially suppressed as in the case of my hands on the stones) ? – usumdelphini Jul 16 '12 at 3:56 Isn't the clapping of hands an example for no. 2? – mart Jul 16 '12 at 7:59 @usumdelphini The details of what happens in each of the two bodies are exceedingly important to the nature of the sound (volume, spectrum, duration...). Consider the distinctive sound of a high quality bell or gong: it implies that there are modes in the body of the object with very high $Q$ values. Talk to a percussionist. – dmckee♦ Jul 16 '12 at 13:35 @mart Er...I would have though that most of the sound of clapping came from flesh on flesh, but can provide nothing concrete to back up that assertion. – dmckee♦ Jul 16 '12 at 13:39