Here are some pictures from the construction of Sound Logic LLC.    You can see that we built our recording studio from the ground up!    Each wall contains 2 layers of 5/8" sheet rock, then a 2 by 8 stud wall (staged and filled with R45 insulation) Then a 3" air gap then the same thing all over again.   No room is toughing another in Sound Logic.   There were over 500 sheets of 5/8" sheet rock.   There are 4 feet of insulation in the ceilings and the floors are floating on neoprene strips.  The doors weigh over 200 lbs each!