We're building an addition to our house and the contractor only insulates the outside walls so it passes inspection. I wanted to insulate the interior walls and floor to help reduce room to room noise. I don't want to install resilient channels because they would charge us more for the drywall installation. What's a good cheap insulation material for 2x4 constructions? Does the higher r-value usually correspond to a higher sound transmission value? I noticed they had a few packs of r-19 insulation that said "acoustical insulation". Should I buy some of those instead of the regular home depot insulation? You don't really need a vapor barrier for interior walls right. What type/thickness of insulation should I get for the I-Joist between the 1st and 2nd floor?