Michael Schwob

There are many myths about how to improve sound walls.  Just like most myths, they are based on anecdotal evidence and hearsay.  When you are designing a building, you want to be sure that the occupants will have the privacy and noise levels that they expect.  That is the measure of success.

Following is a summary of 6 surefire ways to improve the acoustical performance of stud sound walls.  Laboratory test data shows them to be reliable and effective.  If you need a good sound wall, here is how to design it.

1. Add Sound Absorbing Material in the Cavities

Adding sound absorbing material to the cavity of a stud wall is the most basic method of improving the soundproofing performance of the wall.  Sound absorbing material should always be included in a wall design when there is a concern about sound transmission between spaces in a building.

The most common sound absorbing material to use in sound walls is fiberglass batting.  Mineral wool batts and cellulose are less commonly used.  Cellulose does not perform as well as fiberglass or mineral wool batts, but has the advantage that is can be sprayed into an existing wall.

Performance Improvement: A stud wall composed of one layer of 5/8” gypsum board, 3-5/8”, 25 gauge steel studs 16” on center and one layer of 5/8” gypsum board on the other side (a typical commercial stud wall) has a sound transmission class rating less than STC-38.  Add 3” fiberglass batts and the rating will increase to STC-47.

2. Add Gypsum Board

Adding gypsum board to a sound wall increases the mass of the wall.  The soundproofing performance (transmission loss) improves with the addition of mass.  This relationship is so important it is called the Mass Law.

Performance Improvement: Add a layer of 5/8” gypsum board to the STC-47 wall described above and the performance will increase to STC-52.  Add another layer to the other side of the wall and the performance will increase to STC-55.

3. Use Staggered Studs

The studs in a sound wall create a rigid connection between the wallboard on each side of the wall.  This bridge conducts sound energy through the wall better than the air cavities.  Designing a wall with staggered studs reduces this direct connection.

Performance Improvement: Replace the single stud in the STC-47 wall described above with staggered studs having a total cavity depth of 6” and the performance will increase to STC-53.  Add a layer of 5/8” gypsum board on either side of the wall and the performance rating will increase to STC-57.

4. Use Double Studs

Staggered studs share the same top and bottom plates (tracks).  Double studs don’t share the same top and bottom plates.  Double stud walls provide better performance because they completely decouple the two sides of the wall.

Performance Improvement: Replace the single stud in the STC-47 wall described above with double studs having a total cavity depth of 6” (2-1/2” studs with a 1” air gap) and the performance will increase to STC-55.  Add a layer of 5/8” gypsum board on either side of the wall and the performance rating will increase to STC-61.

5. Add Resilient Elements

The original resilient element was the resilient channel (RC).  RC channel is still in use today and is the most widely known resilient element.  I don’t recommend RC for two reasons.  One, because RC is usually not installed correctly.  Two, the market is saturated with products called resilient channel of various designs that are untested.  Be very careful in your specifications and field observation if you plan to use RC.  (This topic deserves its own post.)

New products have been developed that are more reliable and are more effective than RC.  Two notable products are the PAC International RSIC clip and the Kinetics Noise Control Isomax clip.  Reputable companies manufacture these products and third party data is available to verify the reported performance.

Performance Improvement: Add resilient clips to the STC-52 wall described above (one layer of 5/8” gypsum on one side and two layers on the side with the clips) and the performance will increase to approximately STC-58.  Adding clips will increase the thickness of the wall by 1.32” to 1.63” depending on the product used.

6. Use Engineered Wallboard

Engineered wallboard takes the place of gypsum board in the design of a wall.  It is specifically engineered to have a high sound transmission loss.  Most are composed of layers of various materials that provide more mass and/or more acoustic damping than typical gypsum wallboard.

There are many verities of engineered wallboard available.  These have different levels of performance, cost and ease of use.  Tight specifications should be used if you are counting on the performance of one of these products.

Two manufacturers who provide engineered wallboard for acoustical applications are Serious Materials and Supress Products.  They manufacture wallboard from 0.5” to 1” or more that exceed the performance of standard gypsum board.  Acoustic data (available on the manufacturer’s websites) should be reviewed with respect to your project.

Performance Improvement: Replace the gypsum board on one side of the STC-47 sound wall described above with Serious Materials QuietRock 525 (also 5/8” thick) and the performance increases to approximately STC-55.  Other wallboard products manufactured by both companies provide even greater performance.

Other Ways to Improve the Design of Stud Sound Walls?

There are other ways to improve the design of sound walls.  This post focuses on the most effective verifiable (surefire) methods.  I have excluded other methods that provide very small performance improvements or are not verifiable with reliable data.  I have also excluded methods that are not performance enhancers as much as fixes for performance detractors.

If you have any further information on surefire ways to improve the design of stud sound walls, please post a reply.