Setting Sonic Traps

Most studio owners and engineers understand the importance of good acoustics.
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Real Traps MegaTraps and Modular System

Most studio owners and engineers understand the importance of good acoustics. If you place microphones in a room that has many strong “early” reflections, or has severe bass peaks and nulls, the resulting recording will sound hollow and distant, or boomy or thin. Likewise, when mixing, audible reflections make it difficult to hear small changes in volume, panning, reverb and EQ. Bass peaks and nulls are equally troublesome, requiring frequent trips to the car to tell if a mix is “portable” and sounds good elsewhere.

The small rooms many people use these days are especially difficult, because reflections from nearby surfaces are stronger and earlier than reflections from more distant surfaces in a large room. In a small room, echoes and ambience are louder, and bass peaks and nulls and ringing are more severe. Low-frequency response variations of 30 dB are not only common but also typical for a bedroom-size mixing space. Even larger domesticsize rooms have acoustic problems if any dimension is smaller than about 20 feet. Sound travels at about one foot per millisecond, so reflections from a surface closer than 10 feet arrive within 20 milliseconds (for a round trip). Due to the Haas Window, or Precedence Effect, a reflection arriving within 20 milliseconds blurs the sound and skews the frequency response instead of being perceived as a distinct echo.

The best type of acoustic treatment is broadband, working efficiently over as wide a range of frequencies as possible. But to target the lowest frequencies requires absorbers that are very thick, and optionally diffusors that are at least four to six inches deep. Rooms treated with thin material such as foam or fiberglass only one or two inches thick tend to sound dull yet boomy at the same time. The mids and highs are absorbed well enough, but the lows still bounce around untamed, yielding more relative energy in the room at those frequencies. The poor balance of absorption versus frequency gives an effect similar to cutting the highs and boosting the lows with EQ.


Various RealTraps acoustic treatments in a
client’s installation
Low frequencies are the most difficult to deal with in all small rooms. As explained previously, high frequencies are easily tamed with 2-inch thick absorbers, but peaks and nulls and ringing at low frequencies require very thick bass traps—not just very thick, but enough of them to cover a substantial portion of the room’s surface. Putting typical 15-inch-wide corner traps in the four wallto- wall corners does not cover enough total surface to make a real improvement. Further, rectangular rooms have 12 corners—four where each wall meets another wall, four more where each wall meets the ceiling, and another four where each wall meets the floor. All 12 corners in a room are viable locations for bass traps, as are all wall surfaces. While it’s impossible to make any room perfectly flat, the more bass traps you have, the closer you’ll get. It’s that simple.

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To solve the severe problems at low frequencies in small rooms, in 2003, RealTraps developed a new type of bass trap that employs a thin plastic membrane bonded tightly to highdensity, rigid fiberglass. The membrane has two important advantages: Absorption at bass frequencies is increased considerably, and the traps absorb less at high frequencies. This means you can put enough traps in a room to make a real improvement at bass frequencies, but without absorbing all the mids and highs as happens with foam or plain rigid fiberglass.

The newest RealTraps bass trap is the MegaTrap, and it represents an important evolution of our original membrane design. Besides having a front face 34 inches across for more coverage than typical 2-foot panels, MegaTraps fill the corner completely to be effective down to the lowest frequencies. Even as low as 40 Hz, MegaTraps still absorb about 70 percent of the sound. Further, they’re designed to be stacked one atop the other, so no holes are needed to attach them to walls. Better, a stack of MegaTraps is mostly invisible because it’s a solid surface that blends with the walls.

Many people work in rented spaces, or for whatever reason prefer not to drill even small holes in their walls. So, to complement the non-installing design of MegaTraps, RealTraps has developed what we call the Modular System. This is a series of bass traps, absorbers and diffusors that are all six inches deep—thick enough to allow the various panels to be stable when stacked, without having to be secured to the walls. Non-slip pads are included so the panels don’t shift or slide around.

The last component of the Modular System is RealTraps Diffusors. These are genuine QRD-type diffusors, but they’re also bass traps. Frequencies above about 800 Hz are reflected by each well, producing diffusion, while frequencies below about 800 Hz pass through the front surface to be absorbed by rigid fiberglass behind each well. This solves the long-standing dilemma of whether it’s better to put diffusors or bass traps along the rear wall of a control room. With the Real- Traps Diffusor, you can have both at the same time. The video, Hearing Is Believing, shows acoustic data taken in a small room with and without a full complement of RealTraps Modular treatment. We also recorded a variety of music at the listening position and rear of the room, with and without treatment, so you can hear the improvement without being there in person.

Many people put off treating their rooms because they plan to eventually move to a better space. With MegaTraps and the other RealTraps Modular acoustic products, there’s no longer an excuse to struggle with an acoustically poor mixing environment. If and when you move, simply pack them up and take them with you, just as you would do with your loudspeakers or outboard gear!

Ethan Winer has earned a living as a studio musician, computer programmer, audio engineer, composer/arranger, technical writer and college instructor. He is co-owner of RealTraps. More information on his acoustic research is available at the Realtraps website.

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