Barts, it's actually a whole lot more than soundproofing. The thing is to make the walls rigid, so that they don't flex in response to sound energy, especially sound from the speakers.
If the walls do flex, they act like exceedingly low grade woofers - woofers made of drywall, responding out of phase. Hence Quietrock 545 with embedded sheet steel.
If the walls do flex, they act like exceedingly low grade woofers - woofers made of drywall, responding out of phase. Hence Quietrock 545 with embedded sheet steel.