Excerpt from Ethan Winer, music engineer, link above.
SIDEBAR: HARD FLOOR, SOFT CEILING
The following is from an exchange that took place in the rec.audio.pro newsgroup in May, 2003:
Bill Ruys asked: Why it is recommended to have bare (un-carpeted) floors in the studio? One web site I visited mentioned that a bare floor was a prerequisite for the room design with diffusors and absorbers on the ceiling, but didn't say why. I'm trying to understand the principal, rather than following blindly.
Paul Stamler: Carpet typically absorbs high frequencies and some midrange, but does nothing for bass and lower midrange. Using carpet as an acoustic treatment, in most rooms, results in a room that is dull and boomy. Most of the time you need a thicker absorber such as 4-inch or, better, 6-inch fiberglass, or acoustic tile, and you can't walk around on either of those. Hence the general recommendation that you avoid carpet on the floor and use broadband absorbers elsewhere.
Lee Liebner: the human ear is accustomed to determining spatial references from reflections off of side walls and floor, and a low ceiling would only confuse the brain with more early reflections it doesn't need. Everywhere you go, the floor is always the same distance away from you, so it's a reference that your brain can always relate to.
Top
John Noll: Reasons for having wood floors: they look good, equipment can be rolled easily, spills can be cleaned up easily, provide a bright sound if needed, sound can be deadened with area rugs.
Ethan Winer: In a studio room, versus a control room, a reflective floor is a great way to get a nice sense of ambience when recording acoustic instruments. Notice I said reflective, not wood, since linoleum and other materials are less expensive than wood yet sound the same. When you record an acoustic guitar or clarinet or whatever, slight reflections off the floor give the illusion of "being right there in the room" on the recording. It's more difficult to use a ceiling for ambience - especially in a typical home studio with low ceilings - because the mikes are too close to the ceiling when miking from above. And that proximity creates comb filtering which can yield a hollow sound. So with a hard floor surface you can get ambience, and with full absorption on the ceiling you can put the mike above the instrument, very close to the ceiling, without getting comb filtering.
Dave Wallingford: I've always preferred wood floors for a few reasons: 1) It's easier to move stuff around, 2) You can always get area rugs if you need them, And the main reason: 3) Pianos sound like crap on carpet.
LIVE OR DEAD - WHICH IS BEST AND WHERE?
If you've ever seen photos of high-end recording studios in magazines, you probably noticed that the studio room floors almost always use a reflective material like wood or linoleum. A hard floor gives a nice ambience when miking drums, guitar amps, and acoustic instruments. Likewise, auditorium stages and school band rooms always have a reflective floor surface too. As mentioned earlier, "live" in this context refers only to mid and high frequencies. I cannot emphasize enough the importance of a reflective floor for achieving a natural sound when recording acoustic instruments. If you record in your living room and your spouse refuses to let you remove the carpet, get a 4- by 8-foot sheet of 1/4-inch plywood to put over the carpet when recording. You can cut it in half for easier storage and put the halves next to each other on the floor when needed.
Control room floors are sometimes carpeted, sometimes wood, and often a combination of the two. Ceilings in these types of rooms also vary between fully reflective, fully absorptive, or a mix of surface types. There is no one correct way to treat every room because different engineers prefer a different amount of liveness. However, you should never make a room completely dead because that produces a creepy and unnatural sound. The only time you might consider making a room entirely dead is when treating a small vocal booth or a
very small studio or control room - smaller than, say, ten by ten feet. When a room is very small the reflections are too short to be useful and just make the room boxy sounding. In that case the best solution is to cover all of the surfaces entirely with absorbent material and, for a studio room, add any ambience electronically later.
Top
In a more typical room I recommend a mix of hard and soft surfaces for the walls, with no one large area all hard or all soft. I suggest applying absorbent material to the walls using stripes or a checkerboard pattern to alternate between hard and soft surfaces every two feet or so. This makes the room uniformly neutral everywhere. You can make the spacing between absorbent stripes or squares larger or smaller to control the overall amount of liveness. If you are using 705-FRK rigid fiberglass or an equivalent product, you can cover more of the wall and still control the liveness by alternating the direction of the paper backing. That is, one piece of fiberglass will have the paper facing the wall to expose the more absorbent fiberglass, and the next piece will have the paper facing out to reflect the mid and high frequencies. In fact, when the paper is facing into the room the lower frequencies are absorbed even better than when it is faces the wall.
Alternating hard and soft surfaces is also advisable with wood panel bass traps - simply place a fiberglass absorber between each trap. You can see this arrangement in the photo of my studio (above Figure 7), where each type of bass trap alternates with the other type and with fiberglass panels. That is, first is a low-bass trap, then a fiberglass panel, then a high-bass trap, then fiberglass, then low-bass, and so forth. I'll also mention that wood panel bass traps can be mounted horizontally when book shelves and other obstacles prevent placing them vertically. Since the corner formed by a wall and the ceiling, or a wall and the floor, is just as valid as any other corner, mounting a panel trap sideways near the top or bottom of a wall is equally effective.
Of course, many studios do have large live areas, and there's nothing wrong with that! If the room is big enough to avoid short echoes between closely spaced walls, having an entire wall reflective can yield a very big sound. And even in smaller rooms a hard floor with one or more bare walls can be useful. My cello teacher, who is a total audio neophyte, blew me away with the quality of a recording she made in her small Manhattan apartment. She recorded while playing with her back against the corner, facing into the room, using an inexpensive stereo mike placed a few feet in front of her cello. The key to a realistic and present sound, especially for acoustic instruments, is capturing some amount of ambience - even when the reverberation of a large space is not appropriate.
Top
Although it is often desirable to alternate hard and soft surfaces on the walls, I often recommend covering the entire ceiling with absorbent material, especially if the ceiling is low. Besides eliminating floor to ceiling flutter echoes, full absorption can make the ceiling appear
acoustically to be much higher. Most home studio owners cringe at the thought of making their ceilings even lower than they already are, but it really can help the sound. If you cover the entire ceiling with 2- to 4-inch thick 705, suspended with strings or wires to leave an air gap, the room will
sound as if the ceiling were much higher. There's no difference between reflections that are reduced by the greater distance of a high ceiling and reflections from a low ceiling that are reduced by absorption. Using thick, dense fiberglass extends the simulated increase in height to lower frequencies. Where thin fiberglass makes the ceiling appear higher at midrange and high frequencies, using thicker and denser fiberglass with an air gap raises the apparent height at lower frequencies as well.
Another advantage of full absorption on a low ceiling is that it avoids the comb filtering that occurs when miking drums and other instruments from above. Placing microphones high over a drum set or string section puts the mikes very close to the ceiling. If the ceiling is reflective, sound will arrive at the mikes via two paths - the direct sound from the instrument and the same sound after being reflected off the nearby ceiling. When the difference in distance is very small, let's say one foot, the reflections cause many peaks and dips in the response, which are very audible and can sound like a flanger effect. (When reflections cause a series of peaks and dips, the effect is often called
comb filtering because the frequency response plot resembles a hair comb.) Again, reducing strong reflections from a nearby ceilin