Diego, I DID read it and I'm saying that the sound of sand hitting a Piezoelectric Film Contact Microphone is different from sand hitting sand.

The sound is: sand bouncing off of the material of the microphone, or rubbing against it. Not the sound of sand. You are using 2 objects to facilitate the sounds. Sand + Object = sound of sand and that object.

Your hands pounding sand like a drum is not the sound of sand, it's the sound of your hands, your flesh, hitting sand.

Sand is hitting the glass, *ting!* : you would probably not get the same tone from sand hitting other grains of sand.

So, those are really nice samples of sand hitting a contact microphone or a glass, etc., but it's not 100% the sound of sand, alone... which, like I said above is pretty limited in range.

Technically, most of the time he is recording the sound of the sand on whatever object he's using.

Sand hitting the microphone. Sand hitting the glass. Without an object for the sand to hit and make different sounds, he'd only have the sound of sand hitting sand which is pretty boring.