One of the principles of reducing sound transmission through a wall is to add mass. Unfortunately, walls are already heavy, and to make a big improvement you have to add a lot of mass.
According to the greengluecompany.com which has done these kinds of tests in independent laboratories, "to improve sound isolation by about 10db you would have to quadruple the number of drywall layers on your wall - from one each side, to four on each side." Adding mass combined with other methods is far more effective.
I suspended a ceiling consisting of 2 layers of 5/8 drywall with Green Glue in between and suspended on sound clips, and achieved over 35 db reduction in sound in the room above. I highly recommend you read the their entire web site before making your decision.
According to the greengluecompany.com which has done these kinds of tests in independent laboratories, "to improve sound isolation by about 10db you would have to quadruple the number of drywall layers on your wall - from one each side, to four on each side." Adding mass combined with other methods is far more effective.
I suspended a ceiling consisting of 2 layers of 5/8 drywall with Green Glue in between and suspended on sound clips, and achieved over 35 db reduction in sound in the room above. I highly recommend you read the their entire web site before making your decision.