Rule #3: The loudspeaker and listener positions in the room affect the audibility of room resonant modes.
Room resonant modes are reinforcements and cancellations at certain frequencies that create peaks and dips in the frequency response, which can add an unnatural boominess to the sound. When room resonant modes are less audible, the bass is better defined, and midrange clarity increases.
Speaker and listener position also affects the amount of bass the listener hears because of standing waves. These are stationary areas of high and low pressure in a room. If the listener is sitting in a standing-wave peak, the bass will be boomy. If sitting in a standing-wave null, the sound will be thin and lacking weight. The solution to either problem is to move the listening seat forward or backward until you hear just the right bass balance.
A well-known rule of thumb states that, for the best bass response, the distance between the loudspeakers and the rear wall should be one-third of the length of the room (Fig. 2). If this is impractical, try one-fifth of the room length. Both of these positions reduce the excitation of standing waves and help the loudspeaker integrate with the room. Starting with these basic configurations, move the loudspeakers and the listening chair in small increments while playing music rich in low frequencies. Listen for smoothness, extension, and how well the bass integrates with the rest of the spectrum. When you find the loudspeaker placement where the bass is the smoothest, you should also hear an increase in midrange clarity and definition.
Rule #4: The farther out into the room the loudspeakers are, the better the soundstaging particularly depth.
Generally, the farther away from the rear wall the loudspeakers are, the deeper the soundstage. A deep, expansive soundstage is rarely developed with the loudspeakers near the rear wall. Pulling the loudspeakers out a few feet can make the difference between poor and spectacular soundstaging.<small>