Retrofit sound insulation between levels

[Leland S.]

I'm looking to reduce the sound between two levels of a townhome, as I rent them separately, but they were built with standard drywall on the ceiling. The second story is supported by 1.5" open joists. 

After some research, I've come up with the following:

- Blown-in insulation to fill the joists with hard-packed cellulose
- Add asphalt panel board layer across the entire ceiling to the existing drywall and fill the cutouts. 
- Add a second layer of 5/8's drywall to the asphalt board. 

It was suggested that I use sound caulk for a second layer of drywall, but I think the asphalt board will help dampen the lower frequencies more. 

I'll just need 2" screws to reach the old J-boxes in the ceiling for the trimouts. 

I've read the J-boxes also need to be sealed somehow but I'm not sure how. Maybe caulking any gaps or cracks in them should suffice.

Experience appreciated.