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Acoustics 101

SPECIALTY ACOUSTIC CONSTRUCTION MATERIALS

Soundboard is often misunderstood, so I will try to set the record straight here. Many people mistakenly use the term to describe materials like regular gypsum board or even particleboard. When people refer to soundboard, they are usually referring to a product trademarked SoundStop®.

SoundStop® is a brown, compressed paper board that is usually 1/2" thick and is manufactured by Knight-Celotex. The best way to describe it for you here is to say that it is a lot like a sheet of Masonite or pegboard, only thicker and a bit softer. A similar material is Homasote. If you describe SoundStop® or Homasote to your building materials supplier, he or she can probably direct you to it. It is pretty dense, so it makes a good layer in a multi-layered wall configuration. In conjunction with layers of 5/8" gypsum board, 3/4" particleboard or MDF and SheetBlok™, it is really effective at blocking the transmission of sound. (It should be noted that when compared side by side with gypsum board, SoundStop® is not quite as good in a straight up STC comparison. It is not clear what sort of performance Homasote offers versus gypsum board or SoundStop®. Bearing that in mind, SoundStop® is good if you want to change up the composition of the layers in your construction. This will dissipate resonances well. However, for sheer mass, gypsum board is a much more cost-effective alternative.)

Blueboard is also a very misunderstood material. This is typically an expanded polystyrene board that's been dyed blue, though there are also pink versions available. It's all the same—mostly useless in terms of acoustical isolation. The density of the material is very low and the material itself is a closed-cell foam. Thus, there is no mass benefit to be gained for isolation and no absorptive benefit to be gained when using it in wall cavities. Unless there is a specific code requirement for this type of material in your construction, we would encourage the use of glass fiber or mineral fiber insulation products in lieu of blueboard.

Glass fiber insulation comes in many varieties. The most common is the pink insulation found in many attics, walls and basements. Here's a breakdown of the types of insulation, their densities and their acoustical benefits:

  • R-11 (2" thick) through R-30 (6" thick) "batt" insulation is very common. It has a density somewhere between 0.7 and 1.0 pounds per cubic foot (pcf) and usually comes in rolls. It is very effective at minimizing cavity resonances (resonances that occur in the air spaces between framing members). It is the minimum insulation that should be used in the walls, ceiling and floor of any studio construction.

  • Board insulation is available from the various companies that specialize in the manufacture of insulation materials. It is typically yellow in color and 2'x4' or 4'x8' in size with thicknesses varying between 1/2" and 4". You may hear it referenced using Owens-Corning's "700 series" designations, e.g., "703" and "705." It is more effective than "batt" insulation at combating cavity resonances. It also has a mass advantage since it is offered in densities from 2.0 to 8.0 (or more) pcf.

  • Either of the above can be purchased with kraft paper or "FRK" (foil-reinforced kraft paper) facings on one or both sides. Two advantages the facings offer are (a) ease of handling and (b) decreased high frequency absorption. The latter is achieved only if the material is not physically inside the wall, ceiling or floor. Thus, if you have the option of buying faced insulation, we would encourage it from the simple standpoint of not having to deal with as much of the irritation associated with handling glass fiber materials.

  • Ductboard is a variation of glass fiber insulation, typically 3 pcf and available in 1/2", 1" or 2" thicknesses. There is usually and FRK backing on one side and a black scrim facing on the other. Used inside ducts, this type of material can help minimize turbulent airflow noise in HVAC systems. Since the black scrim facing contains the fibers, it can also be used as a low-cost wall absorber. It should be noted that the 1/2" thick material is rare. The 1" thick material is very common and is the minimum that should be considered for any acoustical application.
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