As you may know, electronics is not an exact science. The real world imposes conditions on the design and function of circuits and components that cause variations in behavior and response. Additionally, what may be a fact today can become fiction tomorrow as technology changes. This is particularly true when electronics is applied to music and especially in areas that are in their infancy such as in the field of surround sound. With that in mind, let’s discuss subwoofer placement for surround mixing. Keep in mind that as yet there are no optimal conditions for surround speaker placement. These are general guidelines based on existing international standards for small to medium sized listening environments. The guidelines for subwoofer placement for 5.1 systems also apply to 2.1 and 7.1 systems.
Positioning the subwoofer(s) can often be a difficult task and the relative locations are not the same for all rooms. A certain amount of experimentation is to be expected, particularly when retrofitting an existing production room. The main requirement is that the location of the subwoofer not be audibly apparent. One method for locating an optimal position is to place the subwoofer(s) near the listening position and play program material with significant low-frequency content. Then, listen at likely subwoofer locations around the room and choose the location that delivers the smoothest bass response. This location is apt to be the best choice for final subwoofer placement. Remember that the signal to the subwoofer is band-limited anywhere from 80 to 120 Hz and that as the crossover frequency rises, the ability to localize the loudspeaker position increases. Because the LFE channel may have content up to 120 Hz, it is recommended that the sub crossover be set at 120 or bypassed (as the bass-management filter will provide the necessary rolloff). However, keeping the crossover frequency for the bass-managed channels low (80 Hz) provides the greatest flexibility in positioning the subwoofer. Control rooms are often set up in a symmetrical design, making it tempting to locate the sub in an equally symmetrical location (for instance, along the center line under the front speaker). However, a symmetrical placement in a symmetrical room often creates symmetrical standing waves and thus, an uneven room response. Placing the sub slightly asymmetrically may produce a more satisfactory result. Using a second sub can also help smooth out uneven room response problems.