Tips and Tricks of Soundproofing and Acoustics of a Home Recording Studio

Professional recording studios spend thousands of dollars to treat their rooms for soundproofing and acoustics. Home recordists who are serious about creating a neutral environment, and who have earmarked funds for this, might construct a floating room, insulate the four walls with special material, and purchase movable baffles. But more likely than not, you'll spend your money on more tangible items, such as a spare hard drive or a software-based sampler.

For our hypothetical room, we'll consider several approaches to taming sound, none of which costs very much money or requires that much effort or expertise. Even hanging a winter coat in the corner or facing an acoustic guitar toward an overstuffed couch instead of the wall can help you either reduce reflected sound or isolate an instrument when recording.

For the computer recordist, the philosophy of room sound is sort of a black-and-white proposition: If you can't make the room an acoustic paradise, then you want to deaden it almost completely and add any ambient treatment (such as reverb) after the fact (i.e., during mixdown), electronically. Because you'll be recording (which can require isolation) and mixing (which should be done in a neutral room), the best compromise is to go for a deadened sound.

It's important to clear up one key issue in matters of room sound: Soundproofing is an entirely different issue from sound treatment. Soundproofing deals with keeping outside sound out and the inside sound in. As simple as that sounds, it can be very difficult and expensive to achieve.

Sound treatment limits itself to only what happens to the sound inside the room and is much more manageable to recordists on a budget. Here, you don't concern yourself with outside sound getting in (such as a nearby train whistle or truck traffic) or inside sound escaping (and bothering housemates and neighbors). There are easy ways around this, such as scheduling and forgiveness. To truly soundproof a room, however, involves construction, cinderblocks, air traps, insulation, floating rooms, decoupling, and other scary-sounding and scientific principles.

This doesn't mean that sound treatment, when done correctly and effectively, is cheap. However, you can achieve varying degrees of success using just sweat equity (which used to be called „elbow grease“) and some inexpensive, readily available materials.

Treat That Sound

Because actual soundproofing is beyond the scope of this article (and because it doesn't actually affect the sound quality of a recording), we'll focus solely on sound treatment. Most of our efforts will be devoted to reducing reflections from the walls and other surfaces in the room. This involves the processes of absorption and diffusion—also known as deadening. This is not so much stomping the life out of a sound as it is neutralizing the room's influence, which can limit the ambient treatment you supply later on in the process (such as during mixdown).

Materialism

A professional studio is built with no parallel surfaces (wall to wall, floor to ceiling) because these pose problematic reflections (called standing waves) that interfere with recording and listening back (monitoring). Because most other rooms in the world do have parallel walls, you have to treat those surfaces to prevent them from reflecting sound in a bad way.

The best way to squelch reflections from the walls' hard surfaces is to place absorbent materials on them. Because hanging shag carpeting from the wall looks tacky, you might consider using acoustic foam from a company such as Auralex (www.auralex.com) that makes scientifically designed acoustic-treatment materials.

Alternatively, you could construct absorptive panels yourself that you can hang like a big picture (the bigger the better). When you're done recording, just remove them and stash them in a closet or behind a couch.

A Panel Discussion

To build a panel, create a 2'x4' frame out of 2×4's and cover one side with plywood. Then fill the frame with insulation, such as regular household R-ll fiberglass batts. Finally, enclose the open side of the frame with a one-inch-thick acoustical board or panel, such as those made by Owens Corning (series 700) or Knauf (Black Acoustical Board). Your panel should look something like this:

acoustic panel

How you hang the panels is up to you, but whether you use dry wall anchors or drive nails into wall studs, be sure to make careful measurements as to where each panel will go. And as always, remember the carpenter's rule: Measure twice, cut once! Where will you put these well-crafted panels? The best place for one or two panels is the back wall opposite the speakers, behind your head. Additional panels can be placed on the side walls, directly facing your ears (see the below figure).

panels placement

Strategically placing absorptive panels like this will help you hear only the direct sound of the speakers, and not the reflected sound, which, when mixed with the direct sound, yields an unrealistic version of what has actually been recorded.

Baffles

A baffle is a partition that prevents sound waves from passing through it, used to keep two regions acoustically isolated from each other. Baffles don't work 100 percent, but used correctly, they cut down on enough leakage or bleed into microphones to make them very useful in everyday recording situations. Several different types of baffles are used in recording. Let's look at the four most popular.

Gobos

The name gobo is applied to a portable, floor-standing baffle that can be moved around to selectively isolate an instrument from bleeding into another area or mic. Whereas wall and ceiling baffles are used for mixing, gobos are used for recording. You often find guitar amps heavily guarded by gobos because their loud volume and speaker-generated sound tend to permeate every part of the studio, if not kept in check.

You can turn an acoustical panel into a gobo by creating two „feet“ for it, as pictured below. Be sure to make the gap between vertical pieces just the right width so that the panel fits snugly inside the support.

gobo baffle

Ceiling Baffles

The ceiling is a hard surface, just like a wall, and can often contribute unwanted reflections. Especially if the ceiling is low, a hanging baffle is useful in mixing because it prevents the monitors' direct sound from mixing with the ceiling-reflected sound.

There's no difference in the construction of a baffle meant for the wall versus one for the ceiling, just in the method in attaching it (see the below figure). Alternatively, you could construct a special lightweight frame for a single piece of acoustic board to be your ceiling baffle, using 1×2' framing instead of the much heavier 2'x4's.

ceiling acoustics

Tent Baffles

If for any reason you can't access, influence, or otherwise touch the walls of your room, consider surrounding yourself with sound-absorbent material on three, four, or even fives sides (if you include the area over your head). The tent baffle can be a cozy solution when you have to mark off territory for your workspace in a much larger room.

The easiest way to construct a tent is to attach curtain rods from the ceiling and then hang drapery, curtain, or blankets from them. The heavier the material, the better—and if you can get theatrical curtains, or blacks, that's the best of all. But they're pretty expensive, and of course, the heavier the material, the stronger your support structure must be.

Bass Traps

Acoustic panels and tent baffles are good at preventing mid- and high-frequency reflections, but they're powerless against the oozing low-end frequencies that can creep through your studio.

Bass frequencies can literally move around corners, and to tame them you need special devices called bass traps. Good bass traps can cost several hundred dollars, but you can make your own for relatively little money. Although not as good as a unit designed by Auralex, Real Traps, or other companies specializing in acoustic treatment, a home-made trap is better than letting the low-end menace go unchallenged completely.

An effective bass trap can made out of a large cylinder, which is also called a tube trap. Constructing a tube trap is fairly easy once you secure the right materials (making it look nice is another matter!).

Build a Better Bass Trap

To make a tube trap, start with a large cylinder, three feet in length and about 20 inches in diameter. A good source for this is pipe insulation, which is sold by companies such as Knauf (www.knauf.com) in various configurations. The large diameter helps to mitigate frequencies in the 40–100 Hz range. Make caps for the two ends out of plywood or drywall and caulk them onto the ends of the tube, making an air-tight seal. Then cover the tube with the included adhesive-backed paper or add your own fabric.