Our architect has recommended we double up on plasterboard to get a more solid feel, and improved acoustics.   I've had recommendations to instead have a layer of OSB first then a layer of board. Both for the solidity, but also for affixing things directly to the wall without concern for noggins. This I very much like!   Questions are:   1. Does that combo work well acoustically?   2. What thickness of OSB should be used? 9, 12, 15 or 18mm? Should it varry