Recording - June 2011 - 72

mind that—at this point—an empty room is being considered for math purposes). He did have a pitched ceiling leaning in the right direction which did help in some ways, but here’s what I discovered, and what was clearly demonstrated as we watched how the acoustics were affected in this room. He had ordered and received a kit with the right absorber panels and foam corner bass traps that would be thought to eradicate some of the low-end cancellation problems, by trapping and absorbing certain frequencies. When I arrived on the scene his room was set up with his mix desk, a bookcase in the rear, some guitars in the room, and a few pieces of art on the walls. We placed and aimed his near-field monitors in the proper positions and did a spectrum analysis of the room. The low end on the spectrum looked like the math that had been done, and we did see the cancellation occurring and could detect the buildups in the corners and a couple of other areas along the

Guest editorial by Brian Gadson

Be Careful What You Wishsmall-room treatment For: Pitfalls in
You have managed to procure the last remaining room in your house and you christen it your recording cave. You set up all your gear, get a small fridge and find the perfect chair. The only thing left to do is to put up that acoustic panel and basstrap kit you just ordered online, that one they said you need after you supplied the dimensions of your room on their website. You just know that in a few days from now, when the UPS truck arrives, and after several hours putting up pieces of this beautiful $849 acoustical treatment kit, that you will have the perfect sounding 11' x 9' x 8' room. STOP! I applaud your enthusiastic and careful approach in making sure everything sounds the best it can in your new sanctuary of sound, but I do want to share some interesting insights on small-room acoustics that I have come across time and time again in my work. When the math doesn’t work out I have done the math and set up many small one-room project studios, testing the rooms at every step of the way, and this is what I have found: Small rooms are the most difficult to predetermine using the usual math and laws of physics. Those well-proven formulas and computations work well in rooms of considerable size, where they usually allow me to predict with great accuracy how sound will act and react. But they often don’t work well in really small rooms. I recently did a room for an engineer in his home where he had a small setup similar to the dimensions I described above. From a purely mathematical standpoint this room—on paper—had its expected pitfalls in the lows and low mids. The rest of the math in the midrange looked really okay. (Keep in
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ceiling and adjacent wall locations. So we proceeded to put up the bass-trap corner wedges and panels in the first-reflection areas, to try to reduce any phasing issues. Time for the next spectrum test. To our disappointment the room tested worse, not better. I could clearly see from the spectrum graph that although we were trapping some problem frequencies themselves, the frequency bands next to the center frequency we were going after were also being absorbed, at a level of making the room muddy and unfocused. We removed absorbers one at a time until the power midrange frequencies came back to life. We ended up using only maybe 5 pieces of a 12piece absorber kit spec’d out for the room. Small causes—big effects At one point I remember a couple of people coming into the room while the spectrum was running, and I observed the readout of frequency level changes with two more bodies randomly in the room. In large rooms you won’t see the impact of this as much as you do in small spaces. Everything that is reflecting in small rooms creates all kinds of phasing issues, some of which sometimes actually help as much as they interfere in the room depending on where you are seated. Move a chair, remove a guitar that was hanging on the wall, stack a few equipment cases in a corner, and it all makes your room sound different. With only so much surface area to use for reflection in a small room, it is critical that you don’t use too much of the area trying to absorb, or you wind up going in the opposite direction of what you were trying to accomplish in the first place. Less is more So—if the conventional wisdom and the proven science don’t fully work in small rooms, what can you do? I think it is very important in small rooms to have a recording with a mix that you know inside out. and to use it as you are trying to tweak those finishing touches in the sound of your room. Listen for the focus in the midrange octaves. Absorbers absorb frequencies besides the ones you want to tame, and in a small area that could mean trouble. You may have to put up with just knowing that low-end cancellation exists, and learn to compensate for it. Better to leave the “life” in the room, knowing it is somewhat uneven, and proceed with caution, rather than to make it go too dead—and still uneven. You may even find you have an extra $500 in your pocket! Brian Gadson (gadson@recordingmag.com) is a studio designer and studio owner, recording musician, engineer, and producer, with a general contractor background, available for consultation on studio design and sound issues. Find out more at his company website www.earsneyes.com.

http://www.earsneyes.com

Recording - June 2011

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