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Acoustics 101 - Chapter 2: Materials and Products Discussed
Practical Guidelines for Constructing Accurate Acoustical Spaces

Acoustic Construction Materials and Products Discussed

In Acoustics 101 a few general materials, as well as specific Auralex products are discussed. You may or may not be familiar with all of them, so we will cover them here in detail to get that out of the way! Your local lumberyard or hardware store can probably guide you if you do not know exactly where to pick up the items discussed, just be careful not to let them steer you wrong with substitutions or deletions. What worked once to construct a tight, good–sounding recording studio will always work because sound never changes. Auralex has no interest in reinventing the wheel, which is exactly what we would be doing if we attempted to make claims that were counter to the proven construction techniques that are “out there.” The acoustic construction methods and materials outlined here have proven themselves to work many times over and should prove more than sufficient for your needs.

Also, with few exceptions, do not add multiple layers of the materials specified; in this case more is not necessarily better due to diminishing returns. (For reasons we will cover, going from two layers of gypsum board to four is a good thing. Going from four layers to six or eight, however, might not be worth the added cost/trouble.)

You can construct a perfectly good–sounding, airtight recording studio with common, easily–located materials. There is simply no “magic” material that you absolutely must use if you are to have a good room. The materials discussed herein are available at any decent lumberyard and will not set you back two years’ salary.

Common Acoustic Construction Materials

• Wood and metal studs and joists — construction framing members with which most of you are familiar. The most common framing for walls is either 2x4 wood studs or 3.5” metal studs. Which is more cost effective — metal or wood — will largely depend on the relative price of wood and steel in different parts of the country. For acoustical purposes, metal does offer resiliency benefits worth considering for maximum benefit. For those of you that are not used to building things, bear in mind when figuring your dimensions that lumber is not really the actual dimensions indicated by the name. For instance, a 2x4 is not; it is actually 1½"x3½". A 2x6 is 1½"x5½", etc.
• Gypsum wallboard (“GWB”,“drywall”,“SheetRock” is commonly available in ½" and ⅝" thicknesses. It is far and away the most common building material in North America for interior finish construction. Unless you have a home built prior to the 1950s, you probably have gypsum board finish to your walls and ceilings. (Plaster on lathe was much more common — and incidentally much better for sound isolation than gypsum board — in homes prior to the construction boom of the 1950s.)
• Plywood is usually ¾" (but is available in a variety of thicknesses from larger lumber yards) and is either available with flat edges, or with tongue and groove edges for tight floor construction.
• The Particleboard family:
  • Low density fiberboard, or LDF, is typically called chipboard. It’s the stuff out of which most inexpensive, DIY furniture is made.
  • Medium density fiberboard, or MDF, is more typical of shelving and loudspeaker enclosures. It has some very good acoustical properties and we like using it for many varied applications.
  • High density fiberboard, or HDF, is also available, but is quite rare and quite heavy. Very high–end cabinetry will often employ HDF.
  • Oriented strand board, or OSB, is often used in residential construction as a low–cost floor underlayment.
  • Straight up particleboard is usually a version of LDF, but can also be the name given to a higher grade of OSB.
• Other materials we make mention of in Acoustics 101 include gypsum board screws of various thread sizes and lengths, construction adhesives including vinyl flooring adhesive, silicone caulk, etc. Wherever possible, we have provided make, model and cost information as appropriate for any non–Auralex materials we mention.

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 ½" 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 ⅝" gypsum board, ¾" 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 ½" 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 ½", 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 ½" thick material is rare. The 1" thick material is very common and is the minimum that should be considered for any acoustical application.

Auralex Acoustic Construction Products

• Studio–grade Mineral Fiber Insulation is a special, denser type of insulation that the top studio designers are known to use to improve a room’s level of soundproofing. Its greatly increased density when compared to the traditional, pink, glass fiber insulation makes it more effective at stopping the transmission of sound from one room to another. Plus, our Mineral Fiber features a much higher burning point than standard fiberglass insulation and has a radically lower rate of moisture absorption. Our Studio–grade Mineral Fiber is available in 1", 2", 3" and 4" thicknesses in 2'x4' sheets.
• SheetBlok&trace; Professional Sound Barrier is our proprietary, limp mass, dense, vinyl sound barrier material available in 10'x4' sections or 30'x4' rolls. It weighs one pound per square foot (1 lb/ft²) and is about ⅛" thick. It is flame retardant, easy to install with plastic–cap nails, staples or trowel–applied multi–purpose vinyl flooring adhesive. We also offer SheetBlok–Plus which is the same as SheetBlok, except with a very strong peel–and–stick adhesive backing that makes installation a breeze. SheetBlok is safe, inexpensive, easy to work with, more effective, easy to cut with scissors or an ordinary utility knife and is FedEx shippable right to your door. SheetBlok is quite simply one of the best investments in good sound control that you will ever make. Other SheetBlok links:
  • Installing SheetBlok
  • SheetBlok MSDS – (PDF)
  • SheetBlok Technical Data Sheet – (PDF)
• U–Boats™ Floor Floaters physically decouple (“float”) a floor without having to use rigid mechanical fasteners like screws (and without having to take out a second mortgage!). U–Boats make quick work of floating a floor at a price virtually anyone can afford. They are more cost–effective that the “pucks” that have been used in the past. Famous studios and recording artists are using them and loving them. Many multi–million–dollar studios and home–theaters–of–the–stars are floating on U–Boats and you have heard them at work on numerous chart–topping records. Other U–Boat links:
  • Spacing U–Boats
  • U–Boats and weight of floor
• RC8 Resilient Channel is a piece of specially shaped metal to which gypsum board or other building materials can be mounted to isolate them from the framing members (studs) of a wall or ceiling. One leg of the Resilient Channel attaches to the stud, the other leg to the layer of building material being hung. This isolation helps improve the structure’s ability to achieve greater sound transmission loss. We sell RC8 in bundles of 24 that are FedEx shippable and are available through your favorite dealer. Other RC8 links:
  • RC8 FAQ

Other products discussed:

• Tubetak™ Adhesive
• Foamtak™ Spray Adhesive
• Studiofoam®
• StopGap Acoustical Sealant