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What Is Sound Proofing Drywall?

By Jon Eakes

Sound Proofing is a complex field and, to be successful, it has to do with a whole systems approach that deals with impact vibrations, higher pitched sounds like speech and music, and air paths that can sabotage everything else. Good workmanship is as important as good design. Most traditional soundproofing for residential construction consists of sound absorbing batts in the wall space,
uncoupling of the drywall with resilient channels - perhaps using very heavy drywall or multiple sheets of drywall - and a lot of work at isolating flanking paths like air moving from one electrical box to another.
Resilient channels have always been an integral part of this effort, yet these channels present significant problems. First, they eliminate the isolation of each stud section, connecting all electrical boxes to each other through air paths even if they are located in different stud sections. Sound isolation of each box becomes essential. If screws attaching the drywall to the channels go through to the studs, the resilient effect of the channel is lost. If the channels are hung in the wrong direction, the resilient effect is diminished. Lining up the channels for proper drywall attachment is not always that easy and, once finished, if the home  zowner decides to screw a shelf onto this wall they either compromise the soundproofing by going into a stud or risk the shelf falling off if they simply attach it to the resilient channel.
Those problems are part of what has driven research into a better way to do things. We have recently seen a lot of advertising for Sound Proofing drywall. Sound Proofing drywall panels promise at least a 50 per cent increase in sound attenuation properties over standard drywall. Of course, you pay a premium for this high-tech sound proofing: It costs 5 to 6 times more than regular drywall.

Is it worth it?
Basically, these new panels eliminate the need for resilient channels, although you can still use them if you insist and they will add even more to your Sound Transmission Class (STC) rating, but they will also give you problems with those flanking paths. Because you don't need to use the channels and you can nail or screw soundproofing drywall directly to either wooden or metal studs, there is no loss of floor space or ceiling height. All of these panels cut with a score-and-snap technique just like regular drywall. In a retrofit situation you can create a significant decrease in sound transmission by simply installing it directly over existing drywall. All of these things help to assure good soundproofing without specialized trades care.
Just how do these panels, which come in the same sizes and thickness of regular drywall, manage to do so much? Much in the same way that plywood brought great strength and stability to thin panels of wood by using a laminating technology, Sound Proofing drywall accomplishes its amazement with laminations.
The highest STC rated and most expensive panels have up to five layers of gypsum and other exotic materials designed to deal with different frequencies of sound energy. The basic 1/2" residential panel is far simpler. The first layer or substrate is made of fairly straight forward gypsum material. Then there is a damping layer that can contain gypsum, ceramic, metal and other composite materials. Finally there is a top finish and constraining layer, again basic gypsum. But actually there are more layers in all the panels - the all important adhesive that holds the primary layers together. Unlike plywood where the glue holds it all together, here the flexible glue, called "Tuned Viscoelastic Polymers", lets each layer react differently to the sound energy and rub against each other. The polymers actually convert the friction caused by the acoustic energy (sound) to thermal energy (heat) and, with the sound having been converted to something else inside the drywall panel, there is not much sound left to transmit through the wall.
Sound Proofing drywall simply allows the entire assembly to achieve high STC ratings in less space and with less work. It is not cheap, but it works.

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