DiY Acoustics

IF YOU'VE EVER SCRATCHED YOUR HEAD AND WONDERED why tracks that sounded killer in the confines of your home studio came out bright and brittle, narrow
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IF YOU'VE EVER SCRATCHED YOUR HEAD AND WONDERED why tracks that sounded killer in the confines of your home studio came out bright and brittle, narrow and smeared or boomy and dull-sounding in the car, a club or your friend's living room, you're not alone. Or perhaps it's within the studio that you're experiencing the pain of “cauliflower” ears and seemingly marathon mix sessions due to indecisiveness based on what you're hearing — or what you're not!

Rest assured, at one point or another, everyone goes through the same growing pains of “learning” their speakers and understanding through trial and error what sounds right (and what doesn't) once it leaves the studio. Sometimes, all that's necessary is adapting new techniques at the console, coming to grips with poor mixing habits of old or maybe even forcing some subtle psychological reconditioning; such is the case when switching from the sound of a familiar set of speakers to a new pair, for instance. But if it's just plain bad from the minute you step foot in the room and turn things up or if your mixes continuously translate poorly to other listening environments, then it could be a sign that there's something wrong with your studio's acoustic space.

DISPELLING THE MYTHS

An incorrectly treated studio can not only be detrimental to the sound of your finished product but also cause ear fatigue, depressed enthusiasm during mix sessions, slowed productivity and general lack of creativity over extended periods of time. Big commercial facilities spend hundreds of thousands of dollars getting their sound “right,” almost always involving a ground-up acoustics architecture and custom build. And a large portion of that money goes toward soundproofing or isolation.

Contrary to popular notion, acoustic treatment is not the same as soundproofing. Soundproofing is an extremely expensive ordeal requiring that large airtight walls of great mass be built to completely isolate rooms and minimize transference of sound vibration between adjoining structures. Because low-frequency airborne sounds are much harder to attenuate than high-frequency sounds, bass-heavy urban and electronic music is nearly impossible to stop from penetrating into your neighbor's apartment on a budget that you or I would consider footing. Incidentally, it is for a similar reason that the age-old tales of lining your walls with flimsy, lightweight cardboard egg cartons won't do anything for your room other than make it look like ass.

Fortunately, electronic-music production doesn't require the costly isolation from incoming noise that a conventional recording studio does. In fact, most any acoustical problem that you're likely to experience in your home studio can be easily and cost-effectively remedied using common, everyday materials and items that you probably already own.

Most articles about studio acoustics tend to lecture on heavily using numbers and formulas. That's no fun! Leaving out the scientific lingo and breaking down the five most common sonic plagues of a home studio into common-sense, practical advice, I'll show you how to treat your room for its problems while maintaining a musicality to its sound, not turning it into a broadcast-booth “dead space.” I won't be tackling any major construction (or reconstruction) of your room, either — your landlord probably wouldn't appreciate your efforts anyway. Rather, these tips may require as little as some furniture relocation and creative accessorizing or a few hours of handiwork on the weekend using some building supplies and a power tool or two.

CONES OF SILENCE

Believe it or not, poor sound in most home studios begins with the speaker setup and a nasty little effect called phase interference. Because sound is a relatively slow mover (much slower than electricity, for instance), should it follow multiple paths of different lengths to get from source to destination, it can easily become out of phase, causing certain frequencies to become attenuated and others emphasized. The problem, as it applies to a speaker setup, occurs when objects in the room set up early reflections and bounce things back to your listening position very soon after the initial sound. Ideally, you want the sound that emanates from your monitors to reach your ears directly, at precisely the same time and with little or no early reflection. Particularly bad is when early reflection times are skewed to one side of the room or deflected off close objects such as your mixing desk or tops of nearby rack cabinets.

The rule is to set up your speakers symmetrically within your room and to form an equilateral triangle with your seated mix position. In a typical rectangular bedroom, you'll find that positioning your mix desk and gear across the width of the room so that your chair is just forward of the midpoint along the room's length yields the best frequency response. Whatever you do, don't position yourself on an angle to the room, and don't place speakers directly into corners. In fact, near-field monitors should be several feet from the wall if space allows. Lifting your speakers off your mix desk is another way to fight phase interference. Decoupling them from the desk's hard surface ensures that bass vibrations from the speaker's enclosure won't set up resonant transmission through your desk and reach your ears faster than through the air.

REPULSIVE REFLECTIONS

The most troublesome of acoustical problems are caused by the repeated reflection of sound off surfaces such as walls, floors and ceilings. A little reflection isn't bad, but too much reflection can not only cause standing waves and frequency “ringing” but also greatly diminish stereo imaging. The three pairs of parallel hard surfaces commonly found in small-room studios are notorious for wrecking sound. Sometimes, you'll luck out with architectural blessings such as angled walls and vaulted ceilings, but more often than not, I've found that every studio can benefit from applying a variety of surface treatments.

Walk into your studio, and clap your hands. Do you hear a distinctive pitched-ringing decay? That's called slap echo. If you hear it (or even if you aren't sure), chances are pretty good that your bare walls could stand for some mid- and high-frequency absorption. It must be used sparingly, though, as a room covered head to toe is rather unpleasant to work in. Rather, you'll want to spot-place absorption in critical areas only and let the sound have room to breathe (pardon the pun). Hanging heavy down comforters or quilted industrial moving blankets on the side walls just to the left and right of the mix position can be quite effective, if only at high-mid to high frequencies. For taming those low-mid frequencies, you'll need a denser, thicker absorptive material. But don't go thinking that standing a bed mattress up there is going to be the solution, either. You see, absorptive materials are frequency-selective, and lining an entire wall (or even a large portion of it) with a single type of absorber is a recipe for acoustical disaster. The response of your room will take on a huge notch in only a specific frequency band, leaving it sounding hollow. That's why you need to make both mid- and high-frequency absorbers (see figures below).

HIGH-FREQUENCY ABSORBER >Using straight kiln-dried 2-by-2-inch pine, construct a 2-by-4-foot rectangular frame and screw or nail it down to a ¼-inch plywood backing board of the same external dimensions. Within the framework, cut to size a section of 1-inch-thick rigid fiberglass (such as Owens-Corning nonfoiled “yellow” 703, available from specialty insulation retailers), and secure it to the plywood using nonhardening construction adhesive. To make it look pretty and keep the fibers intact, stretch a durable and sonically porous fabric such as burlap or muslin (double-plied) across the exposed fiberglass, wrapping it around the edges and fastening it to the plywood backing with a power stapler every inch or so. Be sure not to use shiny or tight-weave fabrics, as they reflect high frequencies and defeat the absorptive purpose.

Make three or four of each absorber, and space them out on the walls around the front of the room, behind the speakers, and bring them along the sides of the room in alternating high, mid, high, mid fashion, all the while making sure that they're applied equally on both sides to keep the room acoustically symmetrical. I suggest hanging them using standard picture-frame wire and wall hooks for a portable solution. This allows you to set up hooks in various areas of your room and temporarily move a panel or two over to a corner where you record vocals, for instance. Their weight should be enough to keep them from rattling, but if they do resonate audibly against the wall during loud playback, tack double-sided foam strips to the plywood backing or cover it completely with felt so that it doesn't mark the walls.

MIDFREQUENCY ABSORBER >To capture the middle frequencies, you will need to use a thicker and denser insulation. I am partial to 4-inch-thick mineral-wool insulation for this application, and I use Roxul brand in my studio. Use the same construction techniques as for the high-frequency absorber, but this time, use 4-by-1-inch pine for the frame to allow for the thicker insulation while lightening the framework.

In addition to constructing frequency absorbers, you can break up flat surfaces by installing objects called diffusers. Typically applied on a studio's back wall, diffusers have many individual chambers or blocks of varying depths that are used to scatter the direct sound that comes from the speakers omnidirectionally throughout the room, greatly reducing repetitive echoes that lead to standing waves. Because the sound is only broken up, not absorbed, diffusers tend to create a pleasant live sound at the back of the studio that complements the absorptive measures used at the front and sides.

Commercially available diffusers are quite expensive, so most home-studio owners come up with their own creative solutions. One that works well is to place a large set of bookshelves against the back wall and line them with books, sculptures and storage canisters of various sizes. For diffusers to be effective though, they should be quite large — covering as much of the wall as possible — and with repetitively spaced chambers. Again, if you're at all handy with power tools, you can construct a modular diffuser system that can grow as you find time to build it and can go with you when you move. Click here to view figure.

BROODING BASS

Unfortunately, no matter how much absorption and diffusion you install, none of it will control a tubby room. The physics of bass boom is simple: All walls are somewhat flexible, and bass frequencies cause them to resonate like a drumhead. When low frequencies collide and stack up, they create tremendous pressure nodes that increase bass levels even more. Controlling this phenomenon is especially important with bass-heavy electronic music, as boomy-sounding rooms will cause you to cut too much low EQ out of your mixes, not to mention cause indistinguishable bass notes. The solution is something called a bass trap. Just as the name implies, its job is to trap bass frequencies like a sponge before they get the chance to bounce back and forth between parallel walls and set up a tsunami of standing waves. Once again, there are dozens of proven bass-trap designs, but the most effective solution requires absolutely no construction and minimal purchases. (see figure below)

BASS TRAP >Buy a large rubber 30- or 40-gallon trash can at least 3 feet tall and without any holes in its bottom, sides or lid; then, line its circumference with bats of high-density mineral insulation (same as used for the absorbers), and loosely zigzag one or two more bats inside, being careful to leave large air pockets. Caulk around the rim of the trash can, as well as the lip of the lid, with nonhardening acoustical caulking or weather sealant, and put the lid on the can. Duct-tape the lid so that it won''t accidentally come undone when you move or bump into it, and feel free to drape a decorative fabric over it. Because bass frequencies collect most in corners, bass traps are often placed in the two front corners of the room. And because bass is omnidirectional, placing them asymmetrically if space is tight won''t diminish their performance one bit.

NOISY COMPUTERS

Although absorption and diffusion can reduce the compounded tin-can effect that an echoic bare-wall room has on ambient noise coming from external hard drives and audio equipment, in all likelihood, you'll still hear the noisy CPU and case fans of your DAW computer. The proper solution to computer noise is not to mask the problem, but fix it at its source. Short of putting the computer inside an expensive isolation box (they cost thousands!) or stuffing pillows and blankets around the case (please don't do this!), your best and safest bet is to try switching out the noisy culprits for less-pollutant brands. I replaced my stock PC fans with the superquiet line of CPU fans from Zalman, which feature wide-diameter fan blades and push volumes of air slowly through enormous copper heat sinks for efficient cooling at close to inaudible noise levels.

CURTAIN CALL

A common complaint of many home studios with windows facing busy urban streets is that even with windows closed, thin single-pane glass is not a great noise blocker. So rather than hang flimsy curtains or rattling venetian blinds — neither of which do anything to muffle the noise — think about hanging a heavy decorative Persian rug on a sturdy curtain rod. This is more of a soundproofing tip than sound treatment, but it will not only look killer and significantly reduce the noise outside but also act as a high-frequency absorber. Got noisy hardwood floors creating a cold echo? Throw a rug there, as well. It's the same effect.

GEOMETRY CLASS

When setting up a studio, most people will be dealing with a standard rectangular room. To create an optimum listening environment, try to arrange your speakers and your listening position in the center of the room. At the very least, you should always try to have some space between the backs of your near-field speakers and the wall behind them.

HIGH-FREQUENCY ABSORBER

Using straight kiln-dried 2-by-2-inch pine, construct a 2-by-4-foot rectangular frame and screw or nail it down to a ¼-inch plywood backing board of the same external dimensions. Within the framework, cut to size a section of 1-inch-thick rigid fiberglass (such as Owens-Corning nonfoiled “yellow” 703, available from specialty insulation retailers), and secure it to the plywood using nonhardening construction adhesive. To make it look pretty and keep the fibers intact, stretch a durable and sonically porous fabric such as burlap or muslin (double-plied) across the exposed fiberglass, wrapping it around the edges and fastening it to the plywood backing with a power stapler every inch or so. Be sure not to use shiny or tight-weave fabrics, as they reflect high frequencies and defeat the absorptive purpose.

MIDFREQUENCY ABSORBER

To capture the middle frequencies, you will need to use a thicker and denser insulation. I am partial to 4-inch-thick mineral-wool insulation for this application, and I use Roxul brand in my studio. Use the same construction techniques as for the high-frequency absorber, but this time, use 4-by-1-inch pine for the frame to allow for the thicker insulation while lightening the framework.

MODULAR DIFFUSER PANELS

Because these will be exposed and on display, use ½-inch-thick stain-grade Russian birch — or maple-veneer plywood. For each diffuser panel, you'll need approximately a 5-by-5-foot section of wood. Your cuts list is the following: two 9-by-35-inch ends; two 9-by-24-inch top and bottom plates; two 1-by-35-inch parts (A and B); two 1.5-by-35-inch parts (C and D); four 8.5-by-35-inch parts (e, f, g and H); one 5.5-by-35-inch part (I); and six 3-by-35-inch parts (j, k, l, m, n and O). Assemble the pieces as shown in the diagram using 1.25-inch brad nails. Use ½-inch-wide iron-on birch- or maple-veneer stripping to cover up all exposed plywood edges; fill nail holes with plastic wood putty; sand; and stain or clear-coat with polyurethane. This builds a 2-by-3-foot-high diffuser panel with chambers 1, 5 and 8 inches deep to handle very low-mid — frequency diffusion with ease. Fasten securely to the studs behind drywall using 2-inch wood screws. The pattern repeats at the ends, so slam as many of these as you like beside each other to cover your back wall, and it will look awesome and totally pro!

BASS TRAP

Buy a large rubber 30- or 40-gallon trash can at least 3 feet tall and without any holes in its bottom, sides or lid; then, line its circumference with bats of high-density mineral insulation (same as used for the absorbers), and loosely zigzag one or two more bats inside, being careful to leave large air pockets. Caulk around the rim of the trash can, as well as the lip of the lid, with nonhardening acoustical caulking or weather sealant, and put the lid on the can. Duct-tape the lid so that it won't accidentally come undone when you move or bump into it, and feel free to drape a decorative fabric over it. Because bass frequencies collect most in corners, bass traps are often placed in the two front corners of the room. And because bass is omnidirectional, placing them asymmetrically if space is tight won't diminish their performance one bit.