Acoustic Treatment for Concrete Walls

Concrete

• The thicker the concrete, the more impervious it becomes to sound. Unfortunately, however, fairly large increases in thickness have only a modest effect on sound transmission, so to block sound completely using concrete alone is impractical -- the thickness required would be much too great. Concealing sand or grout within the core of a concrete block doesn't help much, and adding a material that absorbs sound in place of the sand is no more effective, because the sound waves can travel around the core and skirt the sound-absorbing layer.

Gypsum

• Gypsum boards are a better approach to reducing sound transmission. The gypsum boards often are mounted on wood studs, although long wooden furring strips work as well. As long as there are no holes, the gypsum provides a substantial reduction in sound transmission. Doubling the thickness of the gypsum also confers a slight improvement, and adding fiberglass filler is even better. Metal studs give a "springier" connection and thus an even greater reduction in transmission.

Connections

• It's important to make sure the studs on the two sides of the wall are not connected, because this will also help you minimize how much sound can get through. If the concrete is porous or full of small pores, sealing its surface with plaster also is helpful. Some builders use double-leaf concrete walls with two layers of concrete separated by air rather than gypsum; these can be very effective if properly designed, although they must by necessity be very thick.

Considerations

• Materials that absorb sound at one frequency will not necessarily absorb it at all frequencies. Fiberglass insulation is especially helpful because it absorbs very well across a broad range, and certain foam products sold at audio supply chains are likewise very efficient. Floors should be carpeted and doors sealed with gaskets. You should also be aware that pipes are very efficient conduits for sound. Floor joists in a wooden house are often a route for transmission of sound as well.