Posted by Mark on June 26, 2002 at 13:28:35:
In Reply to: The perfect practice room posted by Patrick on June 26, 2002 at 10:42:41:
500 cubic feet is a recommended minimum for Tuba. The Ideal ceiling would be about 12 feet or so, but this is not possible in most homes. Lesser ceiling heights throw your sound back at you before it is really 'developed'. an angled ceiling, or better yet multi-angled ceiling will help. My practice room is unfortunately just over 7' high, but 12.5'wide x 23.5'long which gives me plenty of cubic volume. I occasionally point my bell at the farthest sidewall to get an idea what I might sound like w/ a higher ceiling. A low ceiling gives you a false impression (both tone and projection) of what you would actually sound like in a 'real' room.
If the room is anywhere under a few thousand cubic feet, you will need to optimize the proportions of the room in order to distribute the room resonances. These resonances (called 'modes') cannot be fixed by curtains, foam panels, egg crate or anything else, because the wavelengths are simply too long for any of those materials to effect. 'Like trying to stop a truck with a pile of shaving cream. Custom Absorbers to control room modes can be created, but are quite large, and custom tuned to the offending frequencies. Not easy or cheap to do. 'Better to design the room right as best as possible.
Bad modal distribution will result in some pitches (or harmoinics) being too dominant in the room , and others will be suppressed. The notes that are too dominant are usually hard to tune, as the fundamental or one of the lower harmonics that the room loves will obliterate everything else.
Modes are generally not an issue in decent large performance rooms.
The best small studio proportions, in order of preference are:
1 x 1.14 x 1.39 (height x width x length)
1 x 1.28 x 1.54
1 x 1.60 x 2.33
1 x 1.40 x 1.90
1 x 1.30 x 1.90
1 x 1.50 x 2.50
1 x 1.50 x 2.50
1 x 1.26 x 1.59
Source: Everest, Alton. "The Master Handbook of Acoustics" 1994 3rd Ed. TAB books
there are others, but these are the top 8. Buy this book; its available in paperback.
If you plug in the room height (as this is the usual limiting factor), just multiply by the other factors to get a good width & length. For example, if the finished room must be 8' high, then take 8 x 1.14 for width, 8 x 1.39 for height, giving a room:
8' x 9'1-1/2" x 11'1-1/2" as one possibility (AT) 811 cubic feet, which is adequate, if sufficient absorption is introduced into the room in strategic locations.
Ideally, I would skew two perpendicular walls at least 7 degrees each so the room is trapezoidal with one 90 degree corner, and the opposite corner at 104 degrees or so. Make the pivot happen from the center of the wall, so the room volume and average proportions will remain about the same. Doing the same with the ceiling is a good idea too, although carpet will prevent any floor-ceiling echoes.
the 7 degree offset is to eliminate the effects of paralell walls, so the absorption can be added wherever it is needed to control frequency balance or modes, rather than requiring you to eliminate echoes.
My room doesn't meet any of these criteria, but it came with the house. I've got enough experience to treat the problems it has. If you have the opportunity of building one, do it right, Particularly if it will be a small room under say 1,500 cubic feet in volume.
Absorption should be the thickest you can get. The folks at Sonex and Auralex Hate for you to know it, but 6" fiberglass insulation outperforms them all, at a fraction of the cost. It ain't as pretty, but works better. Thin absorbers like carpet & 1-2" foam, etc. will absorb overtones, making the room muddy & dead, rather than clear and balanced.
Generally, Corners are a must for absorption, Even if you are striving for a "bright" room. Beyond that, I'd have to know more about the room to tell you where more would be best.
I've said more than you probably wanted to know already, but it costs almost the same to do it wrong. And folks often do it wrong, based on what some guy heard from someone else who knows a guy at the guitar shop who's cousin was in a studio once.
Someday when I have time and a domain (I have neither presently) I want to post a primer on practice room design. Practice room design can be done very well or very badly for about the same cost.
I haven't addressed soundproofing yet. There's plenty in the literature out there. The one thing I would add that many fail to mention: Air-tight. If it can't hold water, It won't hold sound in.
E-mail if any questions.
Mark "used to design these rooms for a living" Mazak