When I walk into a small studio, I often see several things that rank high on the list of typical mistakes made in a room setup. Take a look at your room and see if it has any of the issues listed below. If so, make some corrections.
Symmetry. Speaker placement should be equidistant from all boundaries, and the listener should be seated halfway between the left and right walls. Otherwise, the speakers will have different frequency responses, which will vary depending on the distance to the boundaries. This will cause holes in the frequency response, affecting the mix's center image, and instruments will not sound the same when panned from left to right.
In addition, outboard equipment racks should be set up as symmetrically as possible. If not, they will affect the sound of the bass frequencies in your music. Asymmetry creates a situation that makes it difficult to acoustically treat one speaker without negatively affecting the other, and, as a result, balance will be difficult to achieve.
Speakers on work surfaces. When speakers are sitting on work surfaces or meter bridges, they interact with the surface or console top in a very nasty manner. Most close-field monitors are designed to have a flat frequency response in free space. When the woofers load on a table or console, the amount of bass energy increases, and not necessarily in a linear or helpful way. Also, the high frequencies bounce off of the table or console and reflect back into the engineer's face, mixing in with the direct signal from the speaker. This causes comb filtering and results in cancellations in the mid range and all the way up through the high frequencies.
Flat work surfaces are actually worse than consoles because the sound usually reflects off of a table. At least a console has an angled surface and knobs to break up the extreme high frequencies. This common problem can be solved by purchasing some speaker stands and moving the speakers 1 to 1.5 feet back from the work space. The actual distance will vary depending on your setup, of course.
Too much high-frequency absorption. Have you ever walked into a room and heard your voice coming out of your chest when you talked? This is due to the overabsorption of high frequencies in the room. Many people think that treating a room acoustically means putting 1 to 2 inches of foam on all of the walls. When you do that, however, you suck up all of the high-frequency energy and leave the bass to just roll around the room uncontrolled. This is because you need to affect a quarter wavelength of a frequency in order to absorb it.
For example, because 100 Hz has a wavelength of about 11 feet, you need a lot more than 2 inches of foam absorption to make an impact. Think about balanced amounts of absorption and diffusion and treat only the areas where first-order reflections are a problem.
Filling in for our regular contributor, Nathaniel Kunkel, who is out with an injury this month, is acoustic consultant Bob Hodas, who has tuned more than 1,000 rooms around the world. Visit his Web site atbobhodas.com.