Drywall 101

Quiet rooms matter

Sound dampening can be an important factor when constructing certain types of rooms. For hotels, health care facilities, recording studios, movie theatres, apartment buildings and many other specialty applications, reducing sound transfer between walls, floors and ceilings is critical to the success of these institutions. Even for homeowners, sound dampening ability between rooms is increasingly important in the design of their home. More and more people are building in home mini-theatres, recording or jam studios, quiet rooms for study or relaxations and some are simply interested in blocking incidental noise from the area surrounding their home.

Sound Dampening Techniques

For decades, sound experts have worked to improve the effectiveness and practical implementation of sound dampening processes. Sound dampening technology has changed greatly over the past fifty years but particularly in the past ten years has this field experienced marked improvements. Methods used to control sound transfer across room partitions generally are based on the following principles:

  1. Increasing the mass of the wall partition
  2. Increase the air space of the partition
  3. Add sound absorbing material on or in the partition

Increasing wall partition mass

One technique used to increase room partition mass involves installing lead sheets to walls or ceilings below the finished surface. Adding a layer of lead to a wall greatly increases the wall's overall mass and its ability to block sound. In addition to lead's denseness, lead is relatively pliable which allows it to absorb sound waves thus generally reducing sound transfer across its surface. Although lead may be used at times in industrial applications, it is probably not practical as a solution for large scale sound dampening needs. Lead must be installed exactly according to manufacturer specifications to protect against leaching into the environment due to health risks. Lead material costs are very expensive even before adding the high cost of specific installation.

Mass Loaded Vinyl (MLV) is another product used primarily to increase wall partition mass. . Mass Loaded Vinyl is a very dense and pliable material that serves to increase partition mass and sound absorption. MLV is less expensive than lead and easier to work with. MLV is sold in rolls 4 or 4.5 feet in width of varying lengths. MLV is meant to be installed directly to wall studs or under carpet underlayment. Drywall can be installed directly over MLV to create a finished surface. MLV comes in 1 pound per square foot and 2 pound per square foot thicknesses. Mass Loaded Vinyl is considered to be a limp mass material. Limp mass, in contrast to rigid mass, products are considered to be superior at blocking sound transmission.

A relatively new product that serves to increase wall partition mass but also increases sound wave absorption is QuietRock®, made by Serious Materials Inc. QuietRock is a type of acoustic drywall that uses patent pending technology to absorb sound. It claims to be as easy to score and snap as regular drywall. It installs just like regular drywall and reduces the risk of sound failure due to improper installation. This product is available at some Lowes® home improvement stores. The cost is over six times that of traditional drywall however because it does not requiring resilient channel or other specific methods of framing construction, the overall project costs for material and labor can be even less than other methods.

A simple but often used technique to add mass to room partitions is to add a second layer of drywall to the wall. Drywall may not be as good at absorbing sound waves and is not as dense as MLV or lead but it serves to reduce sound transmission to some extent. Five eighths drywall is most commonly used because it is denser than half inch drywall.

Increasing air space within wall partitions

Other techniques used to reduce sound transmission across wall partitions serve to increase the air space of the partition. Building a double wall with staggered studs increases the air space in the wall thus allowing sound to dissipate within before transmitting to the other side. It basically involves building two walls rather than one. The studs of the second wall are staggered so they do not touch the studs of the first wall. This prevents sound waves travelling through the studs and reverberating on the other side.

Another technique used to increase air space within room partitions is using what is referred to as resilient channel technology. This technique involves installing metal channels perpendicular to the direction of wall studs or ceiling joists. Drywall is installed on the metal channels rather than directly to the studs or joists. When installed correctly, resilient channel can be very effective at reducing sound transfer. The idea is that the sheet of drywall is isolated from the structural framing and therefore sound transmission stops at the drywall and does not continue through the wall.

Resilient channel technology however has drawbacks mostly related to installation requirements. It is all too easy to reduce its effectiveness because of improper installation. For example, screws should not be allowed to come in contact with the studs behind. Drywall installed on the resilient channels should not be allowed to come into contact with the surrounding walls, ceilings or floors. If pictures are hung or electrical boxes are not cared for properly it can cause sound prevention to fail.

Adding sound absorbing material to the wall partition

Damping glues are another material used to reduce sound loss through wall partitions. Two very common brands of damping glue are Green Glue®, made by Green Glue Company a division of Saint-Gobain Corporation, and QuietGlue Pro®, made by Serious Materials Inc. Sound dampening glue is used between two layers of drywall to create a barrier between the two. The glue must be spread liberally on the second layer of drywall before installing over the first layer. When dry the glue dissipates sound preventing it from resonating through the wall.

Probably the most widely used method of sound dampening, because of ease of implementation and cost, involves adding sound deadening insulating bats within wall partitions. Sound dampening insulation can be installed between studs before drywall is installed. This may help to reduce sound transfer slightly but the benefits are very limited. The majority of sound transfer through room partitions travels not through the air space within the wall but by sound vibrations resonating through the structural framing. Sound hits the drywall surface and travels through the studs and on to the other side. Using sound dampening insulation though beneficial is best used as an addition to one of the other methods discussed above.

A word about STC ratings

Sound Transmission Class (STC) ratings describe a material or partitions ability to block sound. This is the most important specification when designing a room to either block-out or block-in sound. In general, a higher number indicates that it works better at blocking sound transfer. Basically, a 2x4 wood stud wall with half inch drywall has an STC rating of around 24. This does very little to block noise transfer and means you can probably hear general conversation across this barrier. A wall with an STC rating of 60 will block most sounds and provide a very sound proof room.

According to STCratings.com, an increase in STC rating of 10 means that apparent loudness will reduce by half. For example, a wall with an STC rating of 40 will sound half as loud as a room with an STC rating of 30. STC ratings are different from NRC ratings. NRC ratings refer to a material or partitions ability to absorb sound. While NRC ratings may indicate a change in STC ratings for a room partition, STC ratings are more important because they more closely reflect the amount of noise that will be noticed by the human ear on the opposite side of a partition.

We at drywall 101 don't provide STC ratings for various sound dampening methods because there is difference in claims across the industry. While sound dampening ratings have been standardized to a great extent, some manufacturers claim greater STC ratings for their products than is realized in the field mostly due to variables beyond the scope of laboratory testing. It is good to be realistic when examining a particular product's claims to block sound. Much depends on the installation process and the surrounding environment. If you are designing a sound critical room, it is recommended that you first speak with an acoustics professional to discuss options.

Creating a sound proof room requires designing a project specific process more so than a particular material. Sound dampening materials and methods of construction can be expensive therefore it is important to do thorough research before starting a project to ensure that all your hard work is not wasted on improper materials or insufficient methods.

Check out some of these links for more information on sound dampening technology for home and industrial applications.

Acoustics.com

Quiet Rock

Super Soundproofing Co