Roundup: Home Studio Acoustic Treatment

Using Diffusors, Absorbers, and Bass Traps
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Musicians have a greater faith in the acoustical properties of everyday materials than is realistically warranted. At some point, we have all considered putting carpet, a mattress, or egg cartons on the wall to tame reflections or in a misguided attempt at soundproofing. Sure, you will notice a difference in sound to some degree using these methods, but you cannot successfully manage the overall frequency response of your studio or create a neutral listening environment by simply scavenging materials from the dumpster.

One way to counteract the negative effects of your room’s dimensionality is by using acoustic surface treatment—paneling of different shapes, sizes, and materials that help you adjust the sonic characteristics of the space without having to resort to a major remodel.

In this article, we will focus on the three basic types of acoustic conditioning that is generally used in home and personal studios—absorption, diffusion, and bass trapping—and walk you through a few representative examples of cost-conscious, effective solutions. Dozens of companies manufacture acoustical products; see the sidebar on page 29 to learn about more options.

MANAGING EXPECTATIONS

Most home and personal studios are located in rooms that are not designed for recording and mixing: A rectangular space with parallel walls and an 8' ceiling brings with it a host of acoustical phenomena—from flutter echo and comb filtering to nodes and standing waves—that make it challenging for you to accurately judge the sound coming from your studio monitors. Rooms that have evenly placed boundaries will display strong resonant characteristics based on the combined dimensions of the space. In addition, when walls, a ceiling, and other surfaces are near your playback system, they create early reflections that can alter your perception of the sound from your monitors, leading you to make EQ and other mixing decisions that won’t translate to other listening environments.

Among the issues that various types of surface treatments can address are boundary reflections and flutter echo (through absorption and diffusion) and standing waves and bass build up (with diffusers and bass traps). However, we are not trying to create an anechoic chamber by removing all of the room’s sonic characteristics: That would be an unpleasant environment in which to work. Rather, the goal is to create a studio that has a pleasing sound and a frequency response that is as flat as possible within the constraints of your budget and room dimensions.

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Although some of these products may resemble consumer-based packaging and standard building materials, acoustical foam and fiberglass products are engineered to deal with precise aspects of sound control and to achieve specific results through the choice of materials, variations in cell size and density, and from the overall shape. Moreover, the products listed here are designed to meet fire and safety standards: If you plan to bring clients into your studio or use these materials in public spaces (such as a school or house of worship) be sure the items you choose meet the appropriate codes.

A full discussion on room acoustics is beyond the scope of this article. However, the manufacturers in this roundup offer resources that you can use to determine the types of treatment you need and where to place them. In addition to the three basic categories covered below, each company makes products designed for more portable sound-control situations, such as mini vocal booths, gobos, and other types of room dividers. But keep in mind that none of these products are designed for sound proofing or isolating your studio from the outside world. To do that will likely require significant changes to the structure if you’re working in a standard home or office environment.

ABSORPTION

To minimize unwanted reflections in the studio, we look to absorption. Generally, absorptive materials are used to treat anomalies that occur in the midrange and high frequencies, which have less energy than bass frequencies and are easier to deal with. The frequency band that is affected by an absorptive panel will depend on the type of material used, as well as its density and thickness: A thin, low-cost foam tile does not produce the same effect as a thick panel of dense, fabric-covered fiberglass.

There are many different types of absorption products that use foam and fiberglass, but there is no one-size-fits-all material. Ultimately, what you get should be based on the frequencies and areas that need treating, the size of the room you’re in, and your budget.

For example, Auralex (auralex.com) offers a broad range of absorption products that are designed to meet nearly every need and price point. The main materials it uses are foam and fiberglass, effective in different ways across the frequency spectrum.

Auralex Studiofoam panels are designed for use in professional (recording studios, vocal booths) and consumer (home theater, school, house of worship) situations for mitigating early reflection, room resonance, flutter echo, and so forth. They come in a wide variety of shapes, colors, thicknesses, and panel sizes; for example, as squares with side-lengths of 1', 2', and 4' in thickness from 1" to 4".

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In addition to flat sheets of foam, the company offers several shapes and configurations that are as aesthetically pleasing as they are acoustically useful. For example, the Studiofoam Wave is a 2'x2' tile with a wave pattern on top that measures from 1" to 3" in height, but with a flat back for wall mounting. The SonoFlat Grid tiles, on the other hand, provides the mid- to high-frequency absorption of the company’s SonoFlat panels, but with a grid of beveled squares on the surface. To create its Sono-Lite panels, Auralex wraps flat Studiofoam panels in fabric, which yields broadband acoustic control.

ProPanel absorbers are Auralex’s line of fabric-covered fiberglass panels. These products have hardened edges, are available in sizes from 2'x2' to 4'x8', and come in a variety of colors. The Carl Tatz Signature Series takes the ProPanel a magnitude further by providing an integrated system of custom-made panels, including the CTD Attenuation Cloud, designed to improve the sound stage by hanging above the mix position, as well as products for controlling the behavior of the mid to low frequencies.

The Auralex Roominator kits, based around the Studiofoam absorbers, include a selection of products designed to treat rooms of a particular size and dimensions. An online calculator is available at Auralex.com to help you select the kit that fits your room and it’s usage: live room, home theater, control room, and so on.

The Broadway line of acoustic panels form the centerpiece of Primacoustic’s (primacoustic.com) absorption products and are available in five main shapes (and from 1" to 3" in thickness)—24"x48" Broadband Absorbers, 12"x48" Control Columns, 2'x2' Control Cubes, 1'x1' Control Blocks, and the 2'x2' triangular and wedge-shaped Accent Panels. The Broadway products utilize fabric-covered fiberglass panels (of 6lbs./cu.ft. density) with resin-hardened edges for stability, and they are easily mounted using the included metal impalers. Although the panels are available in three colors— black, gray, and beige—Primacoustic also offers a line called Paintables, which have a textured latex surface, rather than the fabric wrap, that you can paint to match your environment.

The different sizes and shapes of the Broadway line provide enough variety to handle the absorption requirements of nearly any room size, allowing you to place products exactly where they are needed (rather than having only larger products that could negatively affect room response). To simplify the process of outfitting your studio, Primacoustic created the London series of treatment kits.

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Fig. 1. The intended installation layout of the Primacoustic London 16 kit. The materials in each kit were determined by common room sizes found in personal and home studios, while the design philosophy is based on the concept of a LEDE (live-end, dead-end) studio, where flutter and early reflections are tightly controlled at the main listening position (important for critical decision making) while the other end is more open and simulates a normal listening environment (see Figure 1). The four available kits, which include mounting hardware and screws, are: the London 8, providing 12 panels for rooms of 100 sq.ft.; the London 10 with 20 panels for rooms of 120 sq. ft.; the London 12 with 22 panels for 150 sq.ft. spaces; and the London 16, with a whopping 42 panels for rooms of 200 sq. ft.

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RealTraps (realtraps.com) designed the Mini- Trap panel for either corner or surface mounting using a spacer; this situation leaves an air cavity behind the panel that effectively boosts its absorption capabilities. The panels are 3.75" thick, available in 2'x2' and 2'x4' sizes, and include mounting hardware. MiniTraps can also be mounted on the company’s adjustable stands as well as a mic stand (with hardware available by request).

RealTraps designed the MiniTrap to be semi-reflective at higher frequencies. However, it also offers a high-frequency version of the panel that provides better performance above 200 Hz, but with a slight trade-off on low-end absorption. For mid- to high-frequency mitigation of early reflections, RealTraps sells the MicroTrap, which are available in 2'x2' and 2'x4' sheets. At 1.25" deep, it is thinner than the MiniTrap and doesn’t reach as low in terms of frequency range. However, they can be wall or stand mounted.

As you would expect, RealTraps also offers complete kits tailored to various room sizes and uses— from the Starter, Standard Room, and Mondo Room kits, to product bundles geared towards large rooms and surround configurations. In addition, the company’s modular kits provide single stacked systems: The Mondo Module puts a 2'x4'x6" MondoTrap on a 2'x2'x6" MondoTrap base to create a stacked trap, whereas the Diffusor Module stacks one of the company’s diffusers onto a 2'x2'x6" MondoTrap base.

In addition to its variety of foam and fabric-covered offerings, Acoustics First (acousticsfirst.com) has a slightly more portable absorption solution: The StratiQuilt line is comprised of fiberglass blankets and rolls, 1" and 2" thick, that are designed for situations where flexible and durable panel-curtains are needed. The quilted blankets are available in single-and double-faced configurations, while the rolls are available with bound and unbounded edges.

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DIFFUSION

Diffusers are used to mitigate unwanted resonance and frequency build up by reflecting sound waves into multiple directions, but without reducing the acoustic energy to the degree that absorbers do. A variety of mathematical techniques are used in the design of diffusers, all of which are meant to scatter sound in natural, musically useful, and sonically pleasing ways.

Fig. 2. The Acoustics First Art Diffusor Model D Acoustics First offers a range of 2-dimensional, binary array diffusers it its Art Diffusor line. The company refers to the Art Diffusor Model D as an “organic quadratic diffuser” which is rated with a bandwidth from 599 Hz to above 16 kHz (see Figure 2). The panels are 23.625" square and made from Class A thermoplastic. Other products in the Art Diffusor line include the Model C (thermoplastic) 4-octave diffuser, the Model E (expanded polystyrene) and Model W (wood) 5-octave diffusers, and the Model F (thermoplastic) low-profile diffuser.

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Fig. 3. The Acoustics First Double Duty Diffusor However, a particularly interesting product is its Double Duty Diffusor, a 7"-deep, barrel-shaped (polycylindrical) product that can be used to scatter higher frequencies while trapping low ones (see Figure 3). The center frequency that is greatly affected will depend on the size of the diffuser: The sizes available range from 2'x2' to 4'x8', the latter of which is rated with maximum absorption at 63 Hz. Made of white thermoplastic, Double Duty Diffusors can be ordered with fabric covering and lined with 1.5" fiberglass to mitigate resonance and add absorption.

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RealTraps offers two models of its 24"x48" quadratic residue diffuser—Near and Far; the one you pick will be based on its installed location in relation to the primary listening position. The diffusion wells in the Far model are 6" deep, and the unit is intended for mounting at a distance of 6'or more from the listener, while the Near model is for smaller rooms and has diffusion wells that are 3” deep. According to the manufacturer, the Real- Traps Diffuser is designed to go from diffusion to absorption from 400 to 800 Hz.

As with its absorptive products, Auralex offers several different diffuser lines. The Q’Fusor is a polystyrene product averaging 3" in depth that handles frequencies down to 800Hz, whereas the company’s ProFusor-II puts a similar structure in 2'x2' and 2'x4' fabric-wrapped frames.

One particularly lightweight solution is the T’Fusor Sound Diffusor, thermoplastic tiles (23.75"x23.75"x6") which are engineered for easy installation with pins, nails, tacks, or ceiling drops. The QuadFusor (23.75"x23.75"x6") and smaller MiniFusor (12"x12"x5") are equally easy to mount, but have an open cavity that can be filled with foam or fiberglass to increase absorption.

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Fig. 4. The Auralex Sustain bamboo QuadraTec diffuser At the higher end is the Auralex Sustain line of lightweight and elegant looking bamboo diffusers, designed for ceiling or wall mounting. The QuadraTec is a quadratic-style diffuser sold as a nested pair of 23.75"x23.75"x4.1" panels—like a positive and negative image—intended to be used within the same installation (see Figure 4). The Peak Pyramid diffuser panel is similarly sized but features an uneven polyhedral surface that can be filled with absorptive material to help with bass trapping.

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Grids are also part of the Auralex arsenal of Sustain diffusers. The WaveLens is a 23.75"x23.75"x3" panel consisting of a 7x7 grid of open squares, whereas the grid in the similarly sized WavePrism is filled with tiles at varying heights. The Wave6 kit contains a set of six WaveLens diffusers, and includes the appropriate hardware connectors.

Primacoustic offers an 8x8 open-grid diffuser called the Radiator. Made from Baltic birch plywood and using dovetail joints, the Radiator is engineered with an effective frequency range from 565 Hz to 2.2 kHz. Sized just under 2' square (23.74"x23.74"x3"), it mounts easily into T-bar drop ceilings.

Fig. 5. The Primacoustic FlexiFuser The Razorblade is Primacoustic’s quadratic diffuser, which is designed to work from 425 Hz to 5.5 kHz and provide both spatial and time-based dispersion. The 24"x48"x8" diffuser does this with 17 narrow (1.25") wells, and a combination of MDF slats and a Baltic birch plywood frame.

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A unique product in this roundup is the Primacoustic FlexiFuser, a 24"x48" diffuser with adjustable slats behind which sits a 2”-thick high-density fiberglass acoustic panel for absorption (see Figure 5). You can position the slats to reflect sound away from sensitive areas, while lower frequencies are picked up by the acoustic panel. Because the fiberglass panel is slightly offset from the wall, low-end frequency absorption is further extended.

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BASS TRAPS

Evening out bass response is one of the trickiest aspects of room tuning. Here, the objective is to increase low-end punch and definition as well as achieve a level of accuracy in bass response that allow your mixes to translate to other playback environments.

Because low frequencies accumulate in corners, treatment manufacturers often create products that extend from the points where the walls and ceiling meet. When a bass trap leaves an air gap behind the panel, efficiency is increased without eating up additional space in the studio.

Among the offerings from Auralex for evening out low frequencies are the M224 ProPanels, custom- made 2'x4' fabric-wrapped panels of 2'-thick fiberglass with beveled edges for corner hanging. Similarly, the 24"x24"x3" SonoLite bass-trap panels are designed for corner placement but utilize the company’s Studiofoam technology to control low frequencies.

Fig. 6. Auralex LENRD line of bass traps For much of its Studiofoam line of bass traps, Auralex uses the acronym LENRD (Low-End Node Reduction Device). These include the standard 1'x1'x2' LENRD corner wedges, the 2'x2'x2' MegaLENRD, the 1'x1'x2' DST-LENRD stepped wedges, and the MetroLENRD to fill out the company’s Metro line of products (see Figure 6).

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In terms of simple solutions, Auralex offers the SonoColumn, a 4’ fluted, foam wedge that fits into corners (and can be stacked as well as capped with the company’s SonoCollar accessory) and the Cornerfill and Cornerfill Cube, rectangular and square sections of acoustic foam that can be used to finish off or connect between other acoustic treatment materials.

Designed to be both an affordable and highly configurable treatment, the Venus Bass Traps are 2'x4'x12" tiles with deep wedges that can be mounted flat or in corners. These combine well with other Auralex products, such as the Cornerfill.

Auralex also offers a kit of bass products: ATOM 12 combines a dozen LENRD bass traps with four 12" Cornerfill Cubes to provide a complete bass-management solution.

Acoustics First also offers a variety of foam products for taming low frequency build up, including the PhaseFOAM Box B, Max Wedges, and the Bermuda Triangle Trap. Designed for greater low-end coverage in wall, corner, and ceiling installations, the fabric-wrapped Geometrix Broadband Bass Trap utilizes a 1" 6-7 PCF fiberglass core with a 0.25"-thick 1 PCF blanket. The trap is available in half- and quarter-round shapes.

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Fig. 7. The Primacoustic MaxTrap Primacoustic’s broadband bass traps include MaxTrap (see Figure 7), designed for use in corners, and FullTrap, made for flat surfaces. Both have a sealed enclosure containing a diaphragmatic resonator, which mitigates low-end build up, and are faced with the company’s 24"x48"x3" Broadway panel to deal with issues in the higher frequency spectrum, such as resonance and flutter echo. The manufacturer rates the MaxTrap’s effective absorption to 100 Hz, and the FullTrap down to 125 Hz.

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Primacoustic has other solutions for taming low frequencies, both of which are lower in price and require less space. The wedge-shaped Australis is a solid 12"x36" block of high-density (1.7lbs./cu.ft.), open-cell polyurethane acoustic foam designed for placement in corners or laterally where the ceiling meets the wall. When mounted, the front face of the Australis spans 17” and treats frequencies from 75 to 200 Hz.

The Primacoustic Cumulus is a triangular bass trap that requires less space because it is designed to fit into the corners of a room where the walls meet the ceiling, yet it treats frequencies down to 100 Hz. Made with 2"-thick high-density (6 lb/cu.ft.) fiberglass, each side of a Cumulus trap is 24" long and reverse beveled so that it mounts flush into the corner.

When installed, Cumulus creates an air cavity that extends out from the corner— perfect for capturing low-mid build up. The company also recommends using Cumulus tiles in vocal booths, where frequencies between 200 and 300 Hz can be problematic when recording.

The RealTraps MegaTrap is a triangular bass trap designed for stacking in room corners. With 2' sides that meet the walls, and a 34" face, they are made using the company’s proprietary limp-mass membrane, fabric covered, and available with a 0.25"-thick Masonite top.

Acoustic Treatment Manufacturers

Acoustic Sciences (acousticsciences.com)
Acoustic Systems (acousticsystems.com)
Acoustics First (acousticsfirst.com)
Acoustimac (acoustimac.com)
Auralex (auralex.com)
ClearSonic (clearsonic.com)
Delta H Design (deltahdesign.com)
ESR (zainea.com)
GIK Acoustics (gikacoustics.com)
Golden Acoustics (goldenacoustics.com)
Gretch-Ken Industries (soundsuckers.com)
Hill Acoustic Design (hillacousticdesign.com)
Illbruck (illbruck-sonex.com)
Markertek (markertek.com)
MBI Products Company (mbiproducts.com)
MSR StudioPanel (studio-panel.com)
Netwell Noise Control (controlnoise.com)
Primacoustic (primacoustic.com)
RealTraps (realtraps.com)
RPG Diffusor Systems (rpginc.com)
Silent Source (silentsource.com)
Sound Control Room (soundcontrolroom.com)
Taytrix (taytrix.com)
Vibrant Technologies (vibrantech.com)
Wenger Corporation (wengercorp.com)