The first thing you need to appreciate is the difference between sound shaping and sound isolation. The goal of sound shaping is to tune the acoustics of a room to minimize reflections and absorb certain ranges of frequencies to produce an acoustically flat environment free of echoes. The goal of sound isolation — in contrast — is to prevent sound from entering or leaving an area.
Full sound isolation – that is, soundproofing – is expensive and difficult. I’ve experienced only two fully soundproof rooms. One is a recording studio in Atlanta that floats on a bed of liquid mercury so that the low frequency vibrations from trucks on a nearby highway don’t make it to the microphones. The second is a room used for audiology research in Boston. The 20’ x 30’ room — in the center of the top floor of a high-rise — is suspended by a specially dampened cable and pulley system.
If sound isolation is your goal, you don’t have to float your room on a bed of mercury or suspend it in mid-air if you’re willing to put up with less than perfect results. If you have the luxury of building from scratch, you can use thick fiberglass insulation and double wall construction, along with seamless sheets of rubber between the floor and foundation, and on the walls.
Note that not just any insulation or rubber sheeting will do — use materials rated for sound absorption. A commonly used acoustic metric is the Noise Reduction Coefficient (NRC). A higher number indicates greater absorption. For example, ordinary drywall has an NRC of about 0.05, compared with 1.00 for 2” thick Owens-Corning 703 fiberglass boards.
In addition to insulation, you can also use special shock mounts to attach gypsum board or plywood to wall studs. Double-paned windows will reduce acoustic transfer to or from your neighbors or the street. Regardless of what you use, you’ll find it most difficult to block the lower frequency sounds which are coupled through the foundation and frame of a building.
Sound shaping is less arduous and more easily achieved than sound isolation. If you’re renting or otherwise can’t tear down walls to add insulation and sheet rubber sound barriers, you can mount cotton or fiberglass blankets in doorways, along walls, and on the inside of windows. Thick, heavy curtains will help absorb the high frequency audio transmitted through your windows. Add a few throw rugs to minimize reflections from the floor. Thick moving blankets with grommets are affordable, easily removed sound absorbers that you can use to cover a doorway, window, or a problematic (paper-thin) wall. I’ve had good luck with ‘acoustic’ moving blankets from Movers Supplies ($16; [url=http://www.moverssupplies.com]http://www.moverssupplies.com[/url]).
If you have a modest budget and don’t like the blanket wall approach, you can step up to sound panels which are simply framed fiberglass and fiber wool. The fiberglass or fiber wool attenuates audio and therefore reflections. Standard panels are 2” or 4” thick, and 2’ x 4’ or 2’ x 6’ in size. I’ve purchased fiberglass sound panels from ATS Acoustics ([url=http://www.atsacoustics.com]http://www.atsacoustics.com[/url]) which sells fully assembled fiberglass panels and DIY supplies. A 2’ x 2’ panel with 2” of fiberglass and a burlap covering sells for about $30. Of course, you can go nuts with coverings. The same panel in microsuede is double the price. Moreover, other vendors sell similar panels with even fancier coverings in the $1,000 range.
A popular choice for sound control materials among musicians and audiophiles is acoustic foam. The most popular – and most expensive – option for acoustic foam is Auralex Acoustics ([url=http://www.auralex.com]http://www.auralex.com[/url]). In certain settings — such as a music studio — acoustic foam looks nicer than panels. It’s important to note that acoustic foam isn’t egg carton foam. Acoustic foam absorbs much more sound – that is, has a higher NRC – than the dimpled foam used to pack eggs.
One problem with acoustic foam is that it’s normally attached to walls and ceilings with glue. Auralex foam ships with a permanent adhesive – not necessarily what you want to use if you’re renting. A better option is DAP 18354 Seal ‘N Peel Removable Caulk which is available in a 10.1 ounce caulking gun tube. I used the caulk to mount a few dozen sheets of Auralex foam in my workshop. Unfortunately, the fumes from the curing caulk were so strong — even with good ventilation — that I couldn’t use the area for two days.
Finally, don’t forget about lining your doors with closed cell foam tape. Consider adding weather stripping, or at least a door sweep, to the bottoms of doors leading to your work area. An added benefit of all this insulation and sealing is that you may save money on your heating and cooling bills.
Of course, there are also downsides to sound proofing and shaping. The first is fire hazard issues. Covering your walls with flammable cotton quilting may not be the safest approach to sound shaping. If fire is an issue, consider using all-fiberglass quilts instead of cotton products. They’re considerably more expensive than the cotton variety ($240 for a 4 x 6’ sheet, Amazon), but you won’t have to worry about a spark from your workbench setting off a fire. NV
