Sound proofing existing walls is a hard task. Or is it? Adding sound attenuation insulation to your home is easier than you think.
Choosing The Insulation Material
Because you are adding insulation for the purposes of preventing sound from traveling through certain walls, you are not concerned about the R-value of the insulation material. What you need to consider is the density of the insulation material. Dense pack fiberglass fill insulation material has an installed density of 1.8 lbs per cubic foot while dense pack cellulose insulation has a density of 3.2 lbs per cubic foot. In this case, the cellulose is much denser than the fiberglass and will make a much better sound attenuation barrier.
Drill 1 1/4 inch holes in between the wall cavities. Try to drill on either side of the wall studs so that the drywall is easier to patch later.
Rent a cellulose blowing machine and pick up the recommended supply of cellulose from your building supply store. Insert the dense pack hose into the first cavity and and turn on the machine. Fill the cavity with cellulose insulation, pulling the hose out slightly when it fills up most of the cavity. You will know this by the material starting to back up into the machine. Shut the machines off when there is about 2 to 3 feet of hose left in the cavity and slowly pull the hose out. This allows the material in the hose to finish off the cavity as you pull out the hose. Repeat this for the rest of the cavities until they are all filled.
Install a drywall mesh patch over each hole in the drywall and apply a coat of joint compound with a trowel. Wait for it to dry, sand it, and apply another coat. Perform process until the wall patch is even with the rest of the drywall.
Texture the drywall to match the rest of the wall with a texture spray can from the hardware store. Be sure to cover a few square feet around the patch to blend the texture into he rest of the wall.
Paint the wall and enjoy the privacy the sound and comfort insulation gives you.