Duplex Wall Soundproofing


I’m looking for the most cost-effective and easy to install sound blocking for a musical range of sound. I have a 2′ x 4′ interior wall that I can’t make much thicker than 1 sheet of drywall – currently all sealed up. No bats or insulation. I can take drywall off one side to install something interior OR drill large holes from top plate (non-load bearing) to insert something. Here are my thoughts. Either drill from top and STUFF that newsprint blown-in insulation till capacity and then cover holes with foam and wafer board strips OR rip drywall off one side, spray foam to FILL cavity and double up on drywall on that side.

The wall is 8′ tall, and less than 20′ linear feet long.
Thoughts? Product? Combination of products?
Other better ideas? Experience?



Unfortunately, to increase the STC rating of your wall, you are going to need to increase the thickness of the wall. It is an incredibly common misconception that insulation inside of a stud cavity will stop sound – and it’s just not the case. Unfortunately blocking sound transmission is going to involve some kind of construction like a new layer of sheet rock to make any kind of a difference at all. I really wish it were as easy as popping some holes into the sheet rock, blowing in some kind of fill between the studs and then patching the holes. I would definitely sell a lot more product and be able to help a lot more people not hear sounds from outside of their space.

Ideally, I would suggest the RSIC-1 Clip system to float the sheet rock off of the wall. This is THE most acoustically efficient and cost effective way to increase the attenuation of a wall assembly. Unfortunately you will loose between 2″ – 2 ½” of wall space. If you don’t have that kind of space, I would suggest one of two products. The first would be to install a layer of Green Glue Damping compound on the back of a second layer of sheet rock that would install directly over the existing sheet rock that is on the wall now. This is a newer technology that is designed to act as a layer of elastic between two pieces of sheet rock. It is an effective way to stop sound while not adding too much thickness to a wall. An older, less efficient way is to install a layer of Mass Loaded Vinyl onto the studs and completely cover the wall before you sheet rock. This will increase the mass and density of the wall and will increase the attenuation rate of the assembly. In order to install the vinyl, you will need to remove the sheet rock that exists and install the vinyl directly onto the studs. This product needs the air cavity of the stud wall to be able to move and vibrate in order to do it’s job effectively.

The reason why insulation does not stop sound transmission is because it has very little mass and density – it is mostly air. Sound travels through air, so sound can also easily travel through insulation. Additionally, insulation between studs does not remove the hard-surface to hard-surface path that the sound uses to make it’s way through the wall. When the sound wave hits the sheet rock on one side of the wall it transforms into a vibration. That vibration travels from the sheet rock to the stud and on to the sheet rock on the other side of the wall, kind of like electricity. Whenever there is hard surface contact from one side of a wall to the other, there is a path for the sound to travel through. The vibration quickly flanks the insulation via the stud. You will never find a wall cavity “insulation” or “foam” that has an STC rating because it is not intended to block sound.

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