How to build sound dampening rooms
Sound dampening is important when constructing certain types of rooms. Reducing sound transfer between walls, floors, and ceilings is critical to the success of hotels, health care facilities, recording studios, movie theaters, apartment buildings, and many other industrial or commercial buildings. Most homeowners appreciate the importance of quite rooms. Many people are interested in having an in-home mini theater, recording studio, jam studio, or quiet rooms for study and relaxations. Some are simply interested in blocking noise from the neighborhood or nearby streets.
Sound Dampening Techniques
For decades, sound experts have worked to improve the effectiveness and practical implementation of sound dampening. Sound dampening technology has changed greatly over the past fifty years but the progress made in recent years has led to marked improvements. Methods used to control sound transfer across room partitions generally are based on the following principles:
- Increasing the mass of the wall partition
- Increase the air space within the partition
- 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 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 and installation costs are expensive due to specific installation requirements.
Mass Loaded Vinyl
Mass Loaded Vinyl (MLV) is another product used primarily to increase wall partition mass. Mass Loaded Vinyl is a very dense, pliable material that is used to increase partition mass and therefore it's ability to absorb sound. 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. Drywall can be installed directly over MLV. MLV comes in 1 pound per square foot and 2 pound per square foot thicknesses. Mass Loaded Vinyl is considered a limp mass material. Limp mass, in contrast to rigid mass, products are considered superior at blocking sound transmission.
A relatively new product that is used to both increase wall partition mass and increase sound absorption is QuietRock®. QuietRock, made by Serious Materials Inc. is a type of acoustic drywall that uses patented technology to absorb sound. It is comparatively easy to cut and can be installed just like regular drywall. This product is available at some Lowes® home improvement stores. The cost is over six times that of traditional drywall. However, because it removes the need for other products such as resilient channel, or specific methods of framing, the overall project costs for material and labor can be even less than other methods.
Additional Layers of Drywall
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
The second general method of reducing sound transmission across walls and ceilings is to increase the air space within wall.
Building double walls
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. This technique 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 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. Resilient channel isolates the sheet of drywall from the structural framing and therefore sound transmission stops at the drywall. The physical separation does not allow sound waves to reverberate through the underlying structure to the other side.
Resilient channel technology does have drawbacks. The specific requirements for installation are difficult to follow in every situation. For example, screws are not allowed to come in contact with the structural studs below. Drywall installed on the resilient channels is not allowed to come into contact with the surrounding walls, ceilings or floors. If pictures are hung or electrical boxes are not installed properly, it can undermine the effectiveness of resilient channel causing failure.
Adding sound absorbing material to the wall partition
Sound dampening glue
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 sound absorbent barrier. The glue must be spread liberally on the second layer of drywall before installing over the first layer. When dry the glue dissipates sound, thus preventing noise resonating through the wall.
Sound dampening insulation
One of the most commonly used method of sound dampening involves adding extra insulation to the wall cavity. Because of the ease of implementation and relatively low cost, sound dampening insulation is commonly used in almost all forms of construction. Sound dampening insulation can be installed between studs before drywall is installed.
Adding extra insulation to wall cavities may help reduce sound transfer slightly but the benefits are very limited. The majority of sound transfer through room partitions travels not through the air cavities 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 most effective when used as an supplement to one of the other methods discussed above.
How to understand STC and NRC ratings
Sound Transmission Class (STC) ratings describe a material or partitions ability to block sound. This is the most important thing to consider when designing sound dampening rooms. The ultimate goal is to either block out or block in sound. In general, a higher number indicates that it works better at blocking sound.
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 on the other side. 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.
What are NRC ratings?
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.
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 sound proof rooms requires a project specific design. A good design will include materials and specific installation techniques that have been engineered by an acoustics professional. Sound dampening materials and methods of construction can be expensive. Therefore it is important to do thorough research before starting a project.