Sound Proofing Between Units

[Joel Florek]

I have a 4 unit building I bought this year and have been working on renovations. I just filled the last unit and am getting noise complaints about the sound. I popped a hole in the wall between the bedroom of one unit and the living room of the other and there is no insulation. There are two layers of drywall on each side so I would like to fill the cavity before trying to add an additional layer of sound proofing drywall.

I also have some considerable noise between the two floors. I have a drop ceiling which I could lay insulation on, or I could cut through the old ceiling with a layer of tin to blow in insulation. Any thoughts on what will be more effective?

Im looking for advice on the best type of blow in insulation for sound and suggestions on the ceiling issue.