RealTraps - Audio's Dirty Little Secret

From Pro Sound News, January 2003


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"Many studio owners have no idea their rooms have such a skewed response!"


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The first products RealTraps produced were the wood panel bass traps pictured here. Click the image for a larger version.
By Ethan Winer

If you ask recording engineers to name the most important part of their signal chain, they're likely to answer a state of the art microphone preamp or A-to-D converter, or maybe a vintage tube mike or compressor, or perhaps even a low-jitter external word clock for their DAW rig. I visit many audio newsgroups and forums every day, and the questions I see most often start with "What's the best" followed by Microphone, Preamp, Sound Card, Active Monitors, EQ plug-in, and so forth. There's no denying that audio gear is very sexy! But too many people miss the larger picture and assume that buying yet more electronics is the solution for whatever dissatisfaction they may have with their recording efforts.

These days, all gear is acceptably flat over the most important parts of the audio range. Distortion, aside from loudspeakers and microphones, is low enough to be inconsequential. And noise - a big problem with analog tape recorders - is now pretty much irrelevant with modern digital recording. Indeed, given the current high quality of even semi-pro audio gear, the real issue these days is the skill of the recording engineer. Except for one pesky problem: Far more important than the equipment you use is the quality of the rooms in which you record and make mixing decisions. Top

What's the point in buying a microphone preamp that's flat to within 1/100th of a decibel from DC to microwaves when the acoustics in your control room create numerous peaks and dips as large as 20 dB. throughout the entire bass range? How important really are jitter artifacts 110 dB. below the music when standing waves in your studio cause a huge hole at 80 Hz. exactly where you placed a mike for the acoustic bass? Clearly, frequency response errors of this magnitude are an enormous problem, yet most studio and control rooms suffer from this defect - I call it the audio industry's "Dirty Little Secret." Worse, many studio owners have no idea their rooms have such a skewed response! Without knowing what your mix really sounds like, it is difficult to produce a quality product, and even more difficult to create mixes that sound the same outside your control room.

These peaks and dips occur when sound waves from a loudspeaker bounce off the floor, walls, and ceiling and collide with each other and with waves still coming from the speaker. Which frequencies are boosted and which are reduced depends on the speaker location and room dimensions, and they also change at different places in the room. The principle is identical to how phaser and flanger effects work, except the comb filtering occurs acoustically in the air. Top

Since the frequencies at which peaks and dips occur change as you move around the room, they are impossible to correct with equalization - what helps here hurts over there. Further, dips as severe as 30 or more dB. are common; adding that much compensating EQ boost will reduce monitoring headroom and increase loudspeaker distortion. A much better solution is to reduce the reflections that create acoustic interference by installing bass traps on the walls and ceilings. It may seem counterintuitive that a device designed to absorb bass will increase its level, but this is exactly what happens. By absorbing low frequency waves rather than reflecting them back into the room, bass traps flatten the frequency response and increase the overall bass level.

One of the most effective acoustic absorbers is fiberglass. Everyone is familiar with the fluffy type used for thermal insulation, but compressed fiberglass boards are even better for acoustic treatment because they're denser and absorb more effectively, especially at low frequencies. Unfortunately, even fiberglass boards are impractical for absorbing frequencies below a few hundred Hz. To obtain a useful amount of absorption at the lowest octaves requires a thickness of at least four feet! Therefore, most studio designers favor bass traps that are more efficient and thus more compact - generally panel traps, which are also called membrane absorbers. Helmholtz resonators are used occasionally, but they're larger and absorb a narrower range of frequencies making them less popular. Top

The problem with panel traps is that they are tricky to build correctly, and they're usually installed permanently onto the walls and ceiling. This makes them impractical for smaller studios with limited resources, especially when their space is rented. But panel traps are very efficient and absorb a wide range of low frequencies. I've been building panel traps for recording studios since the late 1970s, and in every case they tamed a room that was unsuitable for mixing into a room that sounded good and was a pleasure to work in. Seeing the need for affordable but effective acoustic treatment, I designed an improved type of panel trap, and in 2002 founded RealTraps to make them available commercially.

The most important improvement was making the traps portable so they can be installed with minimal damage to the walls, and reused if the studio moves. Making them portable also means the same traps can be used in the studio and control rooms, or moved around within a studio to change the acoustics. Another enhancement is building the traps with an angled front panel. As with angled walls, this reduces flutter echoes and ringing at higher frequencies caused by sound waves bouncing back and forth repeatedly between parallel walls. The angled fronts also help the traps absorb a wider range of frequencies. Top

I hope that by shedding light on our industry's "dirty little secret," more studio owners and engineers will realize that the best route to great mixes is being able to hear more accurately, not chasing an ever-elusive trail of yet more recording gear.


Over the years Ethan Winer has earned a living as a studio musician, computer programmer, audio engineer, composer/arranger, technical writer, electronics technician, and college instructor. Read more about Ethan's work with acoustics and bass traps at RealTraps.

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