I don't read French but I think this is what he is using:

Two layers of 5/8" Gypsum board over 2"x4" with a 3 1/2" layer of acoustic insulation with a 1" air space backed by another 3 1/2" layer of acoustic insulation with another two layers of 5/8" gypsum board over 2"x4"'s...

Please correct me if I am wrong.

My .02: Sounds like it should work very well...

Regards,

WhatFurrer

"Meddle not in the affairs of Dragons, for you are crunchy and good with ketchup..."