Yes it will; but, if you don't have the option of sealing and reinforcing the mass of that outer wall, then about all you can do is go heavier on your two inner leaves in order to compensate some for that extra leaf.... Steve
Thanx for the info. Sorry I didn't get back to you quicker. How much more should I build up the inside to make up for the loss with the extra leaf? Drywall sure is cheaper that MDF or OSB..
I'd make sure your inner studwall is isolated from structure, then put at least 3, preferably 4 layers of drywall on the inside. Ceiling will need to match this, so maybe only 3 layers since 4 gets kind of heavy on a ceiling leaf.
doing this will also stiffen the inner leaf, so you'll likely need more bass trapping to even out the room response... Steve