RealTraps - Maximum Studio, Minimum Stress

From EQ Magazine, September 2004

..EQ ACOUSTICS SERIES..

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"Every EQ reader may not have the luxury of owning a house in which to build a dedicated studio room, but those of you who do are in for a real treat."

 

 

 

 

 

 

 

 

 

"The placement of absorbers, diffusors, and the listening position is very specific, with the goal of using as little absorption as possible."

By Ethan Winer and Wes Lachot

Transform part of your house into a super studio.

My previous EQ articles about project studios and acoustics focused on the basics of room treatment, with an emphasis on practical application as well as plenty of related theory. This article brings together all those concepts - and adds several new ones - to present a complete design for the ultimate personal studio.

Every EQ reader may not have the luxury of owning a house in which to build a dedicated studio room, but those of you who do are in for a real treat. For this article I teamed up with acoustics expert Wes Lachot, who has graciously designed the room and provided the blueprints. I'll start by explaining our design goals, then present the plans with detailed instructions. Although the design is ideal for a typical basement, it could be built in a garage or anywhere there's sufficient space to accommodate a room with these dimensions.

THIS TIME IT'S PERSONAL

We consider this design to be a personal studio for several reasons, but mainly because it's a single room that will be used for both recording and mixing. There are many reasons to favor one room over two: Given a fixed amount of space, it's much better to have one room that's large enough to achieve a great low end response, rather than two rooms that are each too small to sound good. Further, it's very difficult to obtain a meaningful amount of isolation between rooms in a typical house unless you invest a handsome sum into building double walls, a rigid hung ceiling, and floated floors.

Since modern DAW software offers an unlimited number of tracks, there's less need these days to make mixing decisions while recording. Just record each microphone to a separate track, and you can sort out the balances later while mixing. Also, many home and project studio owners are interested mainly in recording themselves one track at a time. So for both of these reasons it makes a lot of sense to build one excellent room that's large enough to record other musicians too when needed - including a drum set or even an entire band. Top

Our other goal was to keep the cost of construction and acoustic treatment reasonable. The idea is that by building three simple walls you can create good proportions and non-parallel side walls. Then, for a few thousand dollars, you can buy bass traps, diffusors, and the ceiling cloud materials. If you build these treatments yourself, you can do it for even less cost.

Note that the placement of absorbers, diffusors, and the listening position is very specific, with the goal of using as little absorption as possible. This keeps the room live enough to capture a great recorded sound and make playing more fun for the musicians, while avoiding excess reflections and echoes that compromise accurate mixing. You can add more absorption if you prefer, but you don't have to just to get acceptable results. Also, splaying the side walls makes the room sound much larger than it is because the angled walls avoid flutter echoes while yielding a more pleasing ambience. Top

Click to see a larger version
Figure 1: This is the studio floor plan view. Click the image for a larger version. Click or right-click HERE to download a large (220 KB) high-resolution version suitable for printing.

 

Click to see a larger version
Figure 2: This is the studio elevation view. Click the image for a larger version. Click or right-click HERE to download a large (283 KB) high-resolution version suitable for printing.

 

 

 

 

 

 

 

"The height that dictates the room modes is measured from the floor to the rigid boundary above."

SOUNDS LIKE A PLAN, MAN

Figure 1 shows the basic floor plan with dimensions, and Figure 2 contains the elevation views of the front, rear, and right side walls. You can use an existing wall for one of the studio room walls, or build all four walls. The walls are standard construction using one layer of 5/8-inch sheet rock on 2x4 studs, with fluffy fiberglass between the studs. In a basement or garage bounded by cement or cinder block, building a fourth wall several inches in from the existing outer wall will help the low frequency response, because sheet rock gives some additional bass trapping as it flexes. If you build the fourth wall, be sure to fill the entire gap between it and the outer cement wall with fluffy fiberglass. If isolation to the rest of the house is required, you can use two layers of sheet rock for the walls instead of one, though the added wall mass increases the need for bass trapping inside the room. If you do use two layers for the walls and ceiling, consider suspending them on resilient channels, which will give even more isolation.

The floor should be a hard surface, but you can add area rugs as needed; for example, to place under a drum set to keep it from sliding around. A reflective floor is also ideal when recording acoustic instruments, and it doesn't have to be expensive hardwood. Linoleum, or even painted or stained cement, sounds just as good, and of course those cost much less than wood. Top

This design assumes a ceiling height of exactly eight feet to the rigid boundary above. If you install a sheet rock ceiling to increase sound isolation to the floor above, then the ceiling height is considered to the bottom of the sheet rock. If isolation is not a concern, you'll do better to leave the bottoms of the joists exposed, and simply pack the space between the joists with fluffy fiberglass a foot thick. In this case the ceiling height is the distance to the bottom of the floor above the joists. Regardless of the ceiling type, if it's not exactly eight feet, you must scale all of the other dimensions accordingly, including the listener and speaker positions and the side wall absorber placements. Again, the height that dictates the room modes is measured from the floor to the rigid boundary above. If that height is exactly eight feet, you don't need to scale the other dimensions.

Covering the ceiling entirely with fiberglass is simpler than building the ceiling cloud shown in the plans because it avoids having to hang a grid and buy or make ceiling tiles. The extra fiberglass in the corners around the perimeter also gives additional bass trapping, which is always welcome. You can cover the fiberglass with fabric stapled to the bottoms of the joists, and attach thin wood trim to cover the staples and fabric seams. However, the room might then have too much absorption. We recommend that you attach a reflective border to the joist bottoms that extends around the perimeter of the room - everywhere the plans do not show the cloud. For a border, you can use 1/8-inch plywood or Masonite, or even thin plastic or heavy card stock, painted for appearance. The goal is to reflect mid and high frequencies around the ceiling edges, yet allow bass frequencies to pass through to the fiberglass above. Top

If you need more isolation and use a sheet rock ceiling, you'll build a cloud 8 x 14 feet, centered along the main axis as shown. Hang a standard T-grid eight inches below the ceiling, then fill it with rigid fiberglass tiles one or two inches thick. You can optionally use commercial ceiling tiles made of rigid fiberglass the same thickness, or thinner tiles with fluffy fiberglass batts three to six inches thick laid on top where they won't show. (If you have air ducts above or near the cloud, be sure to cover the fiberglass with fabric or a plastic painter's drop cloth so as to avoid airborne fiberglass particles.) More fiberglass is always better than less because it extends the cloud's absorption to lower frequencies.

For convenient access, two doors are preferred over one, and the extra exit is always a good idea in case of emergency. The doors must be solid core and should be mounted to swing into the room. This makes them flush with the wall when closed and creates a plane that is symmetrical with the opposing wall. The door locations may be shifted slightly along the side walls if needed, but do not put them where they will interfere with the surround speaker locations. Top

 

 

 

"With bass trapping, the more you have, the flatter and tighter the low end will be."

 

 

 

 

 

 

 

 

 

SIDEBAR: DESIGN NOTES

There's a slight live end - dead end vibe with this design, though it does not strictly follow that approach. The front of the room has exactly enough absorption to create a Reflection Free Zone (RFZ), while the rear is entirely hard surfaces, bass traps, and diffusors. I intentionally did not line the walls with extra absorption, preferring to leave that to individual taste. However, every absorber panel shown has a specific RFZ purpose, either for the main stereo speakers or for the center channel and surrounds.

The main speakers should be mounted behind the console as shown, not on the meter bridge, because comb filtering will result from reflections off the console. The front speakers are placed 30 degrees around from the center line of the room, and the surrounds are placed 120 degrees from the center. This puts the front center speaker in an equilateral triangle with the rear surrounds. That is, both the main and surround speakers are the same 30 degrees off axis. I favor this configuration for surround mixing because it's fully symmetrical, and it makes sense sonically to get the surrounds far enough back that the room is covered without the need for 7.1.

The equilateral triangle formed by the three surround speakers is 1.5 (3:2) times the size of the main listening triangle. This proportion falls on the Fibonacci series, whose higher expressions approach the Golden Mean proportion of 1.618. The proportions of the studio itself are derived from the same mathematical series. (The ratios of 13:8 and 21:13 are both very close to 1.618:1.) Another Fibonacci series ratio - 8:5 or 1.6:1 - has received a lot of press. I think of them as slight variations of the same minor 6th musical interval. Two successive minor 6ths comprise an inverted augmented chord, which has good modal spacing for a room with such a high ratio of length to height. This is appropriate for a studio having a low ceiling as this design does. The listening position is also derived from the Fibonacci series, being 8 feet from the front wall and 13 feet from the back wall. In this spot the modal response is reasonable, and the negative effects from rear wall reflections are minimized. --Wes Lachot

ACOUSTIC TREATMENT

Three different types of acoustic treatment are used in this design - mid/high frequency absorbers, bass traps, and diffusors. All of these are in the form of panels 2 by 4 feet, and all are mounted vertically to cover the walls between a height of 2'-8" to 6'-8". Let's look at each of these treatment types in turn.

As mentioned earlier, all of the mid/high frequency absorbers must be placed exactly as shown. You can add more panels if you decide later that you want a less live-sounding room. But those will be in addition to the panels in the plans. The panels shown are intended to avoid all first reflections at the mix position, which is why their placement is critical. The concept of a Reflection Free Zone was explained in my article Improve Your Monitoring in the May 2004 issue, so I won't explain that again here. Briefly, avoiding first reflections improves imaging and is mainly a mid/high frequency issue. For this purpose, 703 or 705 rigid fiberglass or equivalent, two inches thick and spaced two inches off the wall, is adequate. Top

All of the bass traps go in the room corners, and the wall mounting shown in Figure 1 is merely a placeholder. For example, wood panel membrane bass traps must be mounted flat on the walls to work properly, but bass traps such as Auralex LENRDs and RPG's Modex traps are shaped specifically to fit into a corner. Other bass traps, like those from RealTraps, can be mounted either straddling the room corners at an angle or parallel to the walls as shown. Therefore, if you buy commercial bass traps you should follow the manufacturer's recommendation, or those of the trap plan's author if you're building your own. Note that having bass traps in the four wall-wall corners as shown is the minimum we recommend. With bass trapping, the more you have, the flatter and tighter the low end will be.

Finally, the entire center portion of the rear wall is lined with diffusors. Diffusion makes the room sound larger than it really is, and also improves intelligibility by scattering the rear wall reflections to avoid obvious slap echoes back into the mix position. There are many brands of diffusors, and like absorbers, you can build your own, so I'll just offer some general advice. Good diffusors, like RPG's QRD designs, are expensive to buy and difficult to build because their construction is very complex. If obtaining good diffusors is beyond your reach right now, you can instead use mid/high frequency absorber panels where the diffusors are shown. That will avoid slap echoes from the rear wall, and you can replace them with good quality diffusors later. Top

YOU SPEAKIN' TO ME?

The last issue is loudspeaker placement, and as you can see this design accommodates true 5.1 surround mixing. Even if you're not currently doing surround mixing, you may in the future, and it costs no more to plan for that. (When I set up my home theater last year, I was astonished to discover that almost every network television show is broadcast in some form of surround. Trust me - this is the future of audio production.)

The loudspeaker placement must be exactly as shown, but a subwoofer will go wherever you can fit it, or where the model you own sounds best. There are too many variables, such as whether the sub fires out the side or downward, to examine all the possibilities here. Use your ears or follow the manufacturer's recommendation for best placement. Top

The front surface of each main speaker is 3'-4" from the front wall, and 3'-3" out from the center line. The speakers should be focused at ear level, approximately 48 inches above the floor. Note that the 9'-0 dimension shown in Figure 1 is to the point of the triangle 16 inches behind your head when seated at the listening position, with the sound grazing your ears as it travels along the lines shown. All five loudspeakers are the same distance from the listening position, angled exactly as shown in Figure 1.

YOU'VE GOT QUESTIONS, WE'VE GOT ANSWERS

As hard as we have tried, it's nearly impossible to explain every detail of a complete studio design in a single magazine article, or anticipate every construction question the reader might have. Therefore, the authors invite you to visit them in Ethan's Acoustics forum at MusicPlayer.com (see the link below) where you are welcome to ask follow-up questions about the design or construction of this studio. Top

Ethan Winer heads up RealTraps where he designs acoustic treatment. Ethan is also your host at the MusicPlayer.com Acoustics forum. Wes Lachot is a professional studio designer, and you can see some of his many projects at www.weslachot.com.

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