Ethan Winer is a name you may recognize. He's been a published author of audio-related articles since the 70s, and he's a regular contributor to many of the online forums. In 1995, he wrote an article for Electronic Musician that detailed how to build an affordable, low- volume bass trap that actually worked. The latest revision of Ethan's informative article is still available on his personal website (www.ethanwiner.com), and I'd bet it gets a gajillion views per month, given that it ranks #1 in Google for the search phrase "bass trap."
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, Ethan teamed up with friend Doug Ferrara and started a company that manufacturers and sells affordable, ready-to-install bass traps using improved versions of his original published design. RealTraps 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!) Graphs of these tests can be seen at www.kimcheerecords.com/articles/studioacoustics/. 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); considerable 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!