Placing the loudspeakers and listening position correctly is the first step toward getting good sound, especially at low frequencies. While positioning alone won’t eliminate the need for bass traps and other acoustic treatment, it’s an easy and free way to reduce low-frequency response errors and improve imaging. The first step is to identify the ideal listening position within the room, and from there you can determine the best speaker placement.
The method used here is based on the 38 Percent Rule, a theory popularized by acoustician Wes Lachot. Lachot has shown that the theoretical best listening position is 38 percent into the length of the room, when measured from the front wall. This offers the best compromise of bass peaks versus nulls for any given room size. (See Figure 1.)
Understand that 38 percent is only the theoretical best location. It’s a good starting point, but in practice it may not be best due to other factors — wall properties, speaker type and location, or perhaps a mixing console that’s too large to fit that way.
Once you’ve decided where to put your seat, the next step is placing the loudspeakers. The speakers and listening position should define an equilateral triangle, with the distance between the left and right speakers the same as the distance from your head to each speaker. Tweeters should also be at ear level and pointed toward you for the flattest response, because most speakers have a skewed response with less high-frequency output off-axis.
Left-right symmetry in a room is critical for good stereo imaging. If your setup is placed more to one side of the room, instruments and voices coming equally from both speakers will not sound centered as they should. When perfect symmetry is not possible throughout a room, at least aim for symmetry in the front. The most important area is along the side walls between your head and the speakers.
In rectangular rooms, the low bass response is most lacking at the halfway points — halfway between the front and rear walls, halfway between the left and right side walls, and halfway between the floor and ceiling. Therefore, the bass response is worst if you sit in the exact center of the room, at a height that puts your ears halfway between the floor and ceiling. You shouldn’t put speakers along any of those centerlines for the same reason; when a loudspeaker is in a room’s null spot, its output is reduced considerably at low frequencies whose wavelengths are related to that dimension.
The best way to know if small positional changes help or hurt is with room measuring software, such as the freeware Room EQ Wizard program. This lets you experiment with different speaker distances by sliding both speakers along their axes as shown, while measuring the response at different proposed listening spots. Otherwise, simply put the speakers at a distance that’s convenient and sensible for the size of your room while keeping an equilateral triangle. Ergonomics matter too!