Room Mode Calculator
Your studio is a big box. It may be an oddly-shaped big box. It may have doors or walls where you don’t expect it. But it’s really a box.
It’s got a length, a width, and a height. And each direction, and combination thereof, is going to have a number of resonant frequencies. And unless you’ve purpose-built the room to be a studio, chances are it’s going to be a number of really horrible frequencies. These “room modes” come in three flavors – axial, which are the standing waves that bounce front-to-back, side-to-side and floor-to-ceiling; tangential, which bounce from corners to corners parallel to a wall or floor and are about half as strong as axials; and obliques which bounce from one corner to another and are about 1/4th as strong as axials.
It’s a lot of resonant standing waves bouncing around. It can make a big mess of your listening if you’re not prepared for it. Of course, if you’re monitoring on nearfields with your head in the sweet spot, it’s not quite as big a deal as if we were talking a more robust listening room, and let’s face it, few project studio people have midfields and mains soffit-mounted to the walls. Still, if you’re trying to do any detailed work, a good listening environment makes a remarkably big difference. And it’s not too terribly difficult to alter a room in such a way that it helps a lot.
First, you need to figure out what your room modes actually are. That’s what this calculator is for – punch in your room dimensions and you can get a good idea of what the modes are. Plug the numbers in Excel or Openoffice or something and see where there are some clusters – those will be your worst modes. Then, treat your room to deal with these frequencies. Bass-trap absorbers in the corners go a long way toward easing problems – since the corners are where all three kinds of resonant waves intersect. It’s difficult, well-nigh impractical for most, to build and install sub-bass traps – they’re huge, for one thing. So basically most of us will have to deal with an inability to do any room tuning below about 125hz, and even then, most absorber performance goes downhill quickly below about 250hz. Still, rigid fiberglass or mineral wool works pretty well, and is comparatively cheap (you’re going to spend a few hundred on monitor speakers – spending $50-100 on
insulation to make them useful is nothing). You can get acoustic insulation from many sources – Acoustimac, ATSacoustics, and many others sell it by the case for a range of prices. Owens Corning 703 and 705 are the default standards, but there are many other manufacturers – IIG, Roxul, John Mansville and Certainteed, for example, all make various acoustic fiberglass and mineral wool products that are comparable (and even in some cases, slightly better for some applications).
First 50 Modes, in Hz.
Effective Reflectivity of Each Mode
Note: This reflectivity graph is based on a few assumptions – 1) that the room in question is currently empty 2) that it’s covered in drywall and has a standard-pile carpeting and 3) that the room size is reasonable and not some outlandish concert hall or tiny closet. I could only plug in so many reflectivity coefficients.
Spacing of Modes
An awful lot of the legwork for this calculator was done by Chris Whealy, whose “Control Room Calculator” spreadsheet does a heckuva lot more than this thing does. It’s definitely worth checking into if you’re planning on building a studio. And it’s free, free, free!