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Project Studio Acoustics

Andy Hong
Gear Geek and Gear Reviews Editor
Tape Op Magazine

Last updated August 2005

Acoustic treatments for the small recording studio

Last year, I wrote an article about the merits of recording drums at home. In the time span since that article was published, I've been hard at work building and tweaking a small, project-based recording studio that would exhibit some of the positive traits of a home studio—a facility with lots of natural light, easily-modifiable acoustics, and bigger-studio sound despite its living-room-like dimensions.

My colleagues and I chose to build the rooms with bare walls, with the goal of acquiring, building, and experimenting with various acoustic treatments—off-the-shelf and DIY—to afford us easily modifiable sonics, both in the control room and in the main tracking room. The walls themselves were built using standard studio construction methods, so they'll remain more or less unmentioned here. Instead, the focus will be on the treatments being tacked onto the walls or placed inside the rooms.

As we continue to add or change the acoustic treatments in the studio, I plan to make available on this page some of my reviews pertaining to studio acoustics that are being published in the print version of Tape Op magazine. In addition, you'll see here additional notes, measurements, and observations that didn't make it into the print reviews.

Product reviews on this page:

RealTraps bass traps

Primacoustic Primakit acoustical treatment

Primacoustic Freeport acoustic panel

Versipanel Wrap-Around Wall

Acoustical Solutions, Inc.
AlphaSorb Fabric Wrapped Cloud

Acoustical Solutions, Inc.
AlphaEnviro Hanging Baffles

Auralex Acoustics PlatFoam

Auralex Acoustics SheetBlok

RealTraps MiniTraps & MondoTraps

 

RealTraps bass traps

Why are bass absorbers a necessity? Bass reflected off walls leads to standing waves. Standing waves create huge peaks and dips throughout the low end. Without bass absorption on the walls, some spots within the room will have too much energy in certain frequencies and too little in others. These peaks and dips in the low-end response will change as you move around the room. Adding foam or fiberglass to your walls to reduce reflections can compound problems in the low end, because these products tend to work only above bass frequencies. But up until recently, adding bass traps to a project studio was too expensive, took up too much space, and/or required significant amounts of DIY construction.

Recently, bass-trap guru Ethan Winer and friend Doug Ferrara started RealTraps the company to manufacturer and sell affordable, ready-to-install bass traps. Their first products are membrane absorbers that hang on the wall. The SB, LB, and HB models utilize a thin, plywood panel that resonates when low frequency soundwaves hit it. Behind the panel is an airtight space with rigid fiberglass that dampens the panel's resonance. This highly-damped resonance is what absorbs the low-frequency waves and prevents them from reflecting back into the room. The new, fiberglass-paneled MiniTraps work the same way, but at an even more affordable cost-to-benefit ratio. I recently outfitted my studio's control room with twelve RealTraps LB7 and HB7 wood panel traps.

Installation in my control room involved attaching mounting bars (included with the traps) on the wall with toggle bolts and drywall screws (depending on location of traps vs. location of the studs) before simply hanging the traps onto the mounting bars. (I faxed Ethan the plan for my control room, and over the phone, he helped me choose the number of traps and the location of each trap to maximize absorption.) Post installation, I immediately noticed "tightening" of the bass response. I heard "more" bass and less mud. With their angled fronts coming off the wall by about six inches, the RealTraps also provided a good deal of diffusion, reducing some of that small-room "phasing" caused by reflections interacting with the primary sound sources. My ADAM S3-A monitors, already punchy and clear in the low end, sounded even clearer.

Curious to see how the benefits measured, I pulled out my trusty Terrasonde Audio Toolbox and performed RTA and RT60 tests, with and without the bass traps installed. (Another advantage of RealTraps? You can remove them easily and take them to your next studio!) Summary: smoothing of response between 30 and 50 Hz; 3 to 5 dB reduction between 63 to 250 Hz, an area where there was too much bass buildup at mix position (at 100 Hz, there had been a peak that was 8 dB higher than the average SPL); some smoothing from 1.3 kHz on up (diffusion at work); and a measurable reduction in reverb time. What does this mean? It's now much easier to make decisions about the low end than it was before, and tracks heard in my control room translate better when heard elsewhere because my room imparts less of its acoustic signature to what I hear in the room.

If you have a project studio, especially one that's been treated with foam, fiberglass, or rug (yikes!), I urge you to consider adding bass traps to your studio. For the price of a few good mics, you could outfit your studio with RealTraps panel absorbers, and the benefit to the sound of your recordings would be far greater than what you'd gain from spending the same money on gear!

MiniTrap: $199.99 direct; SB, LB, and HB Traps: $479-$599; www.realtraps.com

 

Primacoustic Primakit acoustical treatment

My control room, built into an old engine factory, has some odd shapes and features that make it fairly non-rectangular. Therefore, when we designed the room, we knew that if we used an off-the-shelf acoustic treatment, it would have to be extremely customizable. Primacoustic makes a series of highly-modular, ready-to-install Primakits that make specification and installation incredibly easy, whether you have a normal room or a non-standard space like I do. Five different types of foam modules are included. The installation manual and product brochure (both well-written and informative publications come in the kit), recommend numerous installation patterns and include a good explanation of expected benefits. Engineer and audio-hacker Rachel Uwa and I followed the instructions and had the 13 ft x 18 ft control room treated in four hours. In addition to the foam modules, our London Studio 16 kit came with more foam-safe Liquid Nails adhesive than we needed. Installation onto drywall and brick couldn't have been easier. And sure enough, the different module styles—assembled into "walls"—made for a professional look, despite the "challenging" architecture.

After installation, we ran the same FFT and RT60 tests we'd done pre-Primakit. More importantly, we listened with our own ears and heard an obvious difference. Mud gone. Imaging cleaned up. And as Rachel described the control room sound before we installed the Primakit: "I even had to search to find my low end because the high end was so harsh and distracting." After installation: "Now, the highs are crisp, the midrange is well defined, and the low end is right where it should be." The previous week, I'd recorded drum tracks using a minimal mic setup. With lots of mics on the drums, I oftentimes have to fight the crunchy harshness of the hi-hat bleeding into all the mics-a result of "phasey" comb-filtering. In the pre-Primakit control room, the hi-hat sounded harsh, despite the minimal mic'ing. Post-Primakit, that harshness in the hi-hat completely disappeared. Turns out the phasey-ness that I had heard was a result of uncontrolled reflections in my control room, now subdued by the Primakit.

What about competing products? There are two characteristics of Primacoustic foam that make it stand out as the best of the breed. One I've already mentioned: extreme modularity. The other: unlike other foam treatments, the Primacoustic foam has far less "marketing shape" to it. Anechoic wedges and pyramids made of foam are far less effective than broad sheets or angles (of the same outer dimensions)—with open-cell foam, more material equates to more absorption, and with Primacoustic foam, you get twice as much material. Also, Primacoustic claims that their foam is the densest and therefore the most absorptive. What about rigid fiberglass? Fiberglass has better acoustical properties for a given thickness (and is ASTM fire-rated for industrial applications), but I couldn't find a system utilizing fiberglass that's as modular and easy to install as a Primakit. So when it came to choosing an acoustic treatment for my control room, it was an easy decision: Primacoustic Primakit was the clear winner.

$450-$750 MSRP; www.primacoustic.com

 

Primacoustic Freeport acoustic panel

In my "live" tracking room, I've tried hard to spec out treatments that are easy to mount, unmount, move, and swap, with the goal of an acoustic signature that I change easily. I had a contractor who specializes in building movie sets fabricate a whole bunch of custom gobos, boxes, and hanging dividers for me. They were beautifully made, and they function well. At the same time, I acquired a pair of Freeport freestanding panels. When I give visitors or potential clients a first-time tour of my facilities, they never ask about my custom-made acoustic "furniture," but they always seem to be interested in my Freeports. They usually walk up to them, talk into them at close proximity, crane their head around to look at the back of them, then poke the front of them. I'll admit that I did the same thing the first time I saw a Freeport at a trade show.

Why is the Freeport so interesting? It's just a few sections of high-density foam glued to a 2 ft x 4 ft corrugated-plastic sheet mounted on a stand made up of PVC pipe. Sounds simple, doesn't it? Well, it is simple. But it's executed so well that it looks very cool, and it does a great job of providing "tactical" acoustic treatment.

I find my two Freeports most useful when I'm tracking vocals. They have just the right amount of absorption to tailor the sound of the "room" that makes its way into the vocal mic. Just by varying the placement of the panels around the mic and vocalist, I can make the room sound bigger/smaller, darker/brighter, or harder/softer. At 6 ft tall, the panels will work with most vocalists. You can of course place milk crates (or equivalent) beneath them to temporarily raise them higher. Or you can buy longer sections of PVC pipe (readily available at any hardware store) to make them taller. The Freeports are also useful when tracking acoustic guitar, especially if the guitarist is sitting on a stool—again if you need to vary the sound of the room and if you also want to reduce the amount of vocals reflecting back into the guitar mics. A surprise usage scenario? Room mics for drums. Position so that the plastic side faces the drum kit, and the foam side faces away. Place a mic on the foam side. You'll get less cymbal wash and more "oomph" from the drums. Other uses? Behind your speakers to reduce first reflections coming off the back wall. In front of windows that you don't want to cover permanently. Field recording when you don't have the luxury of a controlled recording environment.

And speaking of using these for field recording, the Freeports are extremely easy to assemble, disassemble, and transport—no tools or instructions required. And if you're a one-man studio operation like I am, you'll appreciate the Freeport's light weight (9 lbs), especially when you're moving the Freeports through small doorways or through the maze of drums, amps, cables, and mic stands that your live room becomes during a tracking session. Also worth noting is the fact that the acoustic foam used for Freeports is impregnated with fire retardant.

Now I kinda wish that I'd had fewer custom-made acoustic panels made and instead invested in a second pair of Freeports. The Freeports not only perform well, but they're so quick to set up. Having a pair of Freeports is like having a variable "intimacy" control for your room that's incredibly easy to tweak.

$300 MSRP pair; www.primacoustic.com

 

Versipanel Wrap-Around Wall

I usually track "basics" with all the players, instruments, and amps in the same room. I find that musicians perform better this way. Unfortunately, the situation can get pretty "washy" with all the sounds bouncing around inside a single room, and the bleed between instruments can sometimes be a liability. Recall my statement earlier about designing my live room so it utilizes moveable acoustic treatments for variable acoustics. Now imagine the excitement I felt when I discovered a wall that I can roll out when needed, vary in shape to divide up my live room into efficient acoustic zones, and roll up for storage when no longer required.

The Versipanel roll-out wall is a flexible, free-standing divider made of life-preserver foam and covered in fabric. Vertical ridges allow the wall to curve, making it easy to form semi-enclosed spaces within a room or to follow the contours of existing walls or furniture in a room. Versipanels are made to order, and can be a maximum of 8 ft tall and 35 ft long. Compared to other foam products, the Verispanel has excellent absorptive properties, most likely due to the extreme density of its foam. And it's incredibly durable, more so than any other acoustic product I've seen.

During a recent two weeks of tracking, I had the opportunity to use two Versipanels to control the acoustics in my live room. While tracking basics, I rolled out a 6-ft tall wall behind the drum kit to tame the reflections coming off the rear wall. I rolled out a 4-ft tall wall in front of the kit to reduce the amount of direct bleed between the drums, amps, and non-corresponding mics. The two Veripanels effectively created a "drum room" within the live room with significant attenuation of first reflections and bleed, allowing me to place my main drum mics a few feet from the kit. I left the sloped ceiling and the upper parts of the two-story tall walls uncovered, so there would still be a good deal of splashy room reverb making its way into the room mics. Of course, the effect on the drum sound was far less pronounced than what would have been accomplished if the drum kit had been in its own tracking room altogether, but that kind of extreme isolation was not what I was looking for. When it came time to do overdubs, the Versipanels were handy for "focusing" the sound of the guitar amp. By varying the "wrap" of the wall around the guitar amp, it was easy to adjust the "tightness" of the amp's sound to suit the character of the guitar part. While recording backing vocals, the Versipanel walls were used to define areas of the room that were dry and areas that were reverby. And I'm now looking forward to utilizing the roll-out walls for an upcoming session with a string section.

$12.50 per sq ft MSRP; www.versipanel.com

 

Acoustical Solutions, Inc.
AlphaSorb Fabric Wrapped Cloud

My control room has an open "A Frame" ceiling with a single steel beam forming the horizontal element of the A. When we designed the room, not only did we choose to keep the ceiling open, but we wanted to highlight the ceiling with upward-pointing flood lights to make the room feel more spacious, (The control room is the only room in the building without windows.) But we also knew we'd have problems with the sloped ceiling focusing first reflections at the listening position, causing anything but a "focused" sound. So I spec'ed out AlphaSorb acoustic clouds from Acoustical Solutions. I ordered four 2'' thick, 6 ft x 2 ft clouds with the lower face and edges wrapped in Guilford fabric and with brackets (suspended-ceiling runners) attached to the upper (hidden) face. Using a system of steel angles, C clamps, and 20 gauge steel wire, I installed these below the aforementioned steel beam. I angled each cloud to minimize reflections at the listening position. (It took me one evening to install the clouds by myself.) The clouds are just wide enough to treat the listening position while still leaving enough open space around them so the room doesn't feel smaller. Sonically, they do exactly what I'd hoped they do. All the usual words come to mind—tight, accurate, focused—without the room sounding too dead. The clouds, which are easy to dent, came via a contract shipping company. They were well-packed and arrived in perfect condition. See Acoustical Solutions' website for fabric choices, custom sizing, and sound-absorption coefficients.

$69-$265 depending on size; www.acousticalsolutions.com

 

Acoustical Solutions, Inc.
AlphaEnviro Hanging Baffles

Over the past few months, I've reviewed a number of moveable products that I'm using in my tracking room to control acoustics. With only one live room that's suitable for full-volume tracking, I wanted as much control as possible in terms of varying the sound of that room to fit the character of the performance that's being recorded. In my article "A Primer on Recording Drums at Home" (Tape Op #31), I described a number of techniques that could be used to make a room sound bigger, including the placement of materials to control bass and midrange. Smaller rooms especially tend to be midrange-heavy. To make my live room sound bigger, I wanted to reduce midrange reverberation without making the room sound dead. After some research, I settled on hanging baffles from Acoustical Solutions. The baffles are PVC plastic "bags" wrapped around sheets of semi-rigid fiberglass insulation. I ordered ten 8 ft tall, 2'' thick AlphaEnviro baffles with grommets on the top edge. The grommets hook onto drywall screws drilled into 2'' pine strips that I mounted on my studio wall. The baffles, which are extremely light, are easy to hang and easy to remove. With the help of two friends, it took less than two hours to hang all the baffles.

How does my room sound with the baffles installed? The PVC reflects higher frequencies, but midrange frequencies pass through the PVC and are absorbed by the fiberglass. (Also, by placing the baffles off the walls by 2'', the absorption efficiency is increased at lower midrange frequencies.) The room still sounds lively because enough high end makes its way around. But there's a huge difference in the midrange. There's much less mud, especially as the track count goes up and the room's sonic signature makes its way into more audio tracks. Before the baffles were up, Gavin McCarthy and Jeff Goddard from Karate (my favorite test subjects) had a hard time playing in the room because it was so midrange reverberant. With the baffles up, the "smear" disappeared. While recording basics for the new Karate album, Geoff Farina expressed, "I love the sound of this room. I can hear everything so clearly."

Other thoughts worth noting. The standard PVC rips easily. While installing one of the baffles, one of the screw heads tore a 1'' slash in the PVC when we tried to hang a baffle onto incorrectly-positioned screws. Ripstop nylon is available as an optional covering. I don't know how it would sound, but it would certainly be more durable. Also, the "look" that the baffles impart doesn't really equate to "professional recording studio." Almost everyone who sees them mentions "school gym." What do I think? I like the look. I never wanted a conventional-looking studio. And I certainly didn't want a conventional-sounding live room. I wanted a room whose sonic character I could adjust as needed, with the option of making it sound bigger than it really is. The AlphaEnviro baffles helped me accomplish that goal. Give Acoustical Solutions a call if you've got the same goal, and check out their website for acoustical data, custom-order pricing, and informative articles on acoustics.

$3 per sq ft; www.acousticalsolutions.com

 

Auralex PlatFoam

In Tape Op #34, I wrote about my studio's lack of floating floors, and how the Auralex GRAMMA isolation platform reduced the amount of bass-amp rumble escaping the main room. I also noted that the GRAMMA had an immediate and very discernable effect on the "tightness" of the sound coming from the bass amp. The GRAMMA utilizes two pieces of high-density PlatFoam to decouple what you place on it from the floor. This same PlatFoam can be purchased by itself in box quantities to float larger structures. 24 pieces of 4 ft long 2'' x 4'' strips come in a box of PlatFoam, along with three tubes of TubeTak adhesive, enough to support an 8 ft x 8 ft area.

Loving the positive effects of the GRAMMA in my studio, I decided to build a 6 ft x 8 ft drum platform for my live room using a box of PlatFoam, 3/4'' subfloor plywood, 2'' x 4'' runners, drywall screws, and a tightly woven rug. (Runners or sleepers aren't normally required—I used the runners to solidify the grooved joint between the subfloor pieces that make up my 6 ft deep platform. My runners don't touch the floor, only the PlatFoam does.) Design goals? Quick build, stable, passable through doorway... and of course, less drum sound making its way out of the studio. Once I'd collected the materials, it took me four hours to build the drum platform by myself.

First my comments in regards to construction. The PlatFoam strips vary in thickness by up to 2 mm. Even with the strips glued six inches apart center-to-center, that variance is enough to make a platform constructed of a single layer of plywood bouncy/flexy. I'd recommend using two layers of plywood glued and screwed together to prevent flex. TubeTak will hold foam onto wood tenaciously, but its immediate stickiness gives you a false impression that the adhesive has already set. The foam will pull away if you try to position your platform before full curing has actually completed. Wait at least 24 hours. Auralex recommends using an electric carving knife to cut their foam. I obtained good results using a hot-wire foam cutter.

My comments in regards to acoustic benefits? I'll make this short. The difference is much bigger than I anticipated. Especially for the "khoof" of the kick drum and the "pwack" of the snare drum—I hear less of them outside of the tracking room. And unexpectedly, I hear much less bleed of the drums in the guitar and bass amp mics. Apparently, a good deal of the drum bleed was being transmitted through solids: across the floor, through the mic stands, and into the mics. The PlatFoam-floated drum platform reduced this thru-solid transmission significantly. Less bleed, more focus, better drum sounds. Design goals accomplished... and then some.

$199 MSRP box; www.auralex.com

 

Auralex Acoustics SheetBlok
sound isolation barrier

The live room in my recording studio has lots of natural light, much of it from two skylights. When we first built out the studio, we skipped treating the skylights because some casual testing proved that any sound that escaped through them just went upwards and wasn't loud enough outside at street level to warrant concern. But the problem turned out to be sound leakage into the otherwise dead-quiet room. Trucks and loud cars could be heard through the skylight while tracking quiet acoustic instruments or vocals. And the sound of rain hitting the skylight's glass sometimes lent a specific mood to a quiet recording, whether appropriate or not. I didn't want to block the skylights, and I didn't want to spend a ton of dough adding soundproof glass (with all the expensive framing required). So instead, I utilized clear SheetBlok.

SheetBlok is an extremely dense, extremely "dead," 1/8'' thick vinyl sheet (sold in 4 ft wide rolls) that's usually sandwiched within walls, ceilings, or floors to act as a sound barrier. It has an STC 27 rating, making it more effective than the same thickness of solid lead at blocking sound. And it's black. Well, it's usually black. While poking around Auralex's website, I found a link to photos of a clear version of SheetBlok utilized as a window treatment. Interesting. I also noted that the text described how some of the windows had cracked due to the tight seal created by the SheetBlok window covers trapping in heat-expanded air. So I came up with a plan. What if I fashioned interior skylight covers made with two layers of clear SheetBlok, with a small hole in each layer—the two holes at opposite corners (and a labyrinthine path between them)—to allow for changes in air pressure (and humidity) within the "air trap."

Between his tracking and mixing dates at my studio, Pat Muecke from the band Pick Ups manufactured the dual-layered SheetBlok skylight covers using furniture-grade plywood for framing. Once the covers were mounted, all problems were solved. No more traffic noise and not even the hint of any rainfall, no matter how torrential the storm outside. And I still get tons of natural light into my studio. I couldn't be happier.

$7 per sq ft, special order; www.auralex.com

 

RealTraps MiniTraps & MondoTraps

In Tape Op #36, I reviewed the panel traps that RealTraps used to manufacture out of wood. In issue #38, Larry Crane reviewed RealTraps MiniTraps, which performed so well (while being easy to ship) that the company stopped making the wood panel traps. Since then, RealTraps partners Ethan Winer and Doug Ferrara have added MondoTraps and MicroTraps to their line.

The MondoTraps are similar in construction to MiniTraps in that they're made of panels of rigid acoustic insulation bonded to a limp-mass membrane, wrapped in cloth, and framed in metal. (This design increases low-frequency absorption by more than half over plain rigid fiberglass of the same density and thickness.)

You may recall in my review of the original wooden traps that even after installation of the bass traps, I still had a fairly big "hole" in the frequency response of my control room between 63-72 Hz due to the axial dimension of the room. I wanted to "fill in" that hole a bit and also reduce the rear wall reflections for band members sitting on the couch in the back of the room. Therefore, over the course of a few months, I ordered and installed six MiniTraps and three MondoTraps for my control room, and more for my live room.

My first test was to place a single MondoTrap in the floor-to-wall corner at the front of the control room, hidden on the far side of the recording console. Using my trusty Terrasonde ATB 1, I generated tones at 1 Hz intervals and measured the response before and after placement of the MondoTrap. I was surprised at how effective that single trap was at filling in my low-end hole. Between 44-89 Hz, the bass response went up an average of 3 dB. After the rest of the traps were mounted (some on the rear wall and wall-to-ceiling corners, and some on the front) another set of measurements showed an increase in bass response of 5-7 dB throughout most of that same range. Furthermore, my secondary goal, reducing the rear-wall reflections for the couch-bound band members, was achieved. Imaging and bass response on the couch were discernibly improved.

I can't say enough about how awesome RealTraps products are. I'm convinced that they're the most cost-effective, off-the-shelf means of treating a small room for low-end acoustics. When people ask me what gear they should buy to improve the sound of their home or project studio recordings, I tell them to buy RealTraps bass traps, because a room with crappy acoustics will give you crappy recordings, no matter what mic or compressor you use. Check out the RealTraps website for all sorts of new additions to the company's product line, including gobos, stands, and even built-in SoffitTraps. Volume discounts and room kits are also explained on the website.

$299.99 direct for a single MondoTrap; www.realtraps.com

 

Addendum: Adding a subwoofer

The problem with relying on nearfield monitors to reproduce the extreme low-end is that the optimal position for the nearfields in terms of imaging and detail (everything but the low-end) may not be the best place for the bass to be generated. The low-end response of the room is most likely to be affected by standing waves as a result of the size, shape, and materials of the room. Standing waves are what cause the peaks and dips in the low-end response. By separating the low-end driver—the subwoofer—from the main left & right monitors, you can move the low-end driver to a position in the room that least excites the room modes (without sitting in a null point) and therefore causes the fewest standing waves.

I installed a Bag End InfraSUB-12 PRO subwoofer in the front of the room (firing toward the rear) so that its baffle is 5.5 ft from the front wall and its center is about 1 ft away from the side wall. Although my console and other furniture limited the placement of the subwoofer, I did have enough leeway so that I could adjust for fewer standing waves.

Now the low-end response throughout the whole room is much more even, and the extreme dips and peaks, especially the one at 63 Hz, are pretty much gone.

 

Last modified: 25 June 2010