Soundproofing a Wall over an Existing Wall Part 1
This is Part 1 of a 2 part series. To move ahead to Part 2, click here.)
When soundproofing a wall over an existing wall, there are two types of noise pollution to bear in mind. They are impact and airborne. Products for soundproofing are regularly classified by which noise they are controlling. Television noise, speech or loud music from stereo sets, are airborne sounds. Vibrations from impact sounds penetrates solid fixtures and includes such things as moving furniture, footsteps or traffic noise. Much of the effort used in soundproofing an area is to block out unwanted sound, although in some new home construction the trend is to build a home theater and install the soundproofing to emulate the natural environment of a commercial theater. There are a couple of options open to the DIY enthusiast who wishes to tackle the job of soundproofing. One way is to increase the mass or thickness of the wall. The other way is to use hat channels for resilient noise absorption.
Step 1: Resilient Channels
Resilient channels may be affixed directly to the existing wall’s surface. The channels will create a gap of approximately 25 mm (one inch) between the existing wall and the new dry wall. The channels are fixed horizontally across the wall and are attached by screwing the lower narrow flange to the wall. The broader upper flange is allowed to “float.” Once the drywall has been attached to the channel, this will act as a shock absorber for any vibrations picked up by the wall. These resilient channels can add typically three, five or more STC (sound transmission class) points to any treated wall. When the drywall is being attached, care should be taken to ensure that the screws go through the channel between the studs and are not screwed into the studs or into the wall as this would cancel the sound absorbing properties of the channel.
Step 2: Using Studs
Another way of creating a drywall sound barrier is by using metal or wooden studs. The metal studs, usually extruded galvanized sheet metal, are commonly used for normal drywall partitioning and will be familiar to anyone who has seen a house under construction. The metal stud is easy to work with, quick, and produces very little mess. Alternatively, wooden studs also 25 mm thick may be attached to the existing wall with screws or nails. Note that both hat channels and studs will mean that some interior space will be lost in the room once the soundproofing has been installed. This should be taken into account when planning the soundproofing strategy. To further increase the absorption of vibrations, a layer of MLV (mass loaded vinyl) matting can be applied to the wall either with glue or with nails before the studs are attached. If the studs are already in position, the matting may be fixed over them before the drywall is attached. The MLV may even be painted. Prepare by cleaning with alcohol then use latex or vinyl paint.