I have a partition wall between two of my bedrooms that has no studs. It’s just vertical planks of flat wood with drywall hung on both sides: no air gap, no insulation. This pretty much gives us close to zero soundproofing between the rooms: normal conversation is fully audible, word-for-word.

We can fix this by tearing down the wall and reframing with studs, adding insulation, multiple layers of drywall, etc., but that costs a good amount of money. One cheaper option I thought of is to just hang something like QuietRock on top of the existing drywall. Do people think that would make any/much difference? Or does the wall need the air gap between studs for any of this to be effective?