If you did a setup of bedroom wall - 2cm airgap - 12.5mm plasterboard - 2cm air gap - 12.5mm plasterboard. you will most likely be more than happy... and you can add more miners to the room as you please without having to spend silly money on custom materials
It's not that simple.
I understand that it works in most cases and for what it is intended for. But if it were that simple, many of the new constructions of houses would not have as many acoustic problems as they do (where neighbors hear each other from one side to the other).
