The 8-inch In-Ceiling Bass Augmentation System (BAS) enhances the low-frequency response of any in-ceiling or in-wall speaker system; this is particularly effective in large rooms. The BAS systems have built-in stereo crossovers. This allows you to connect your in-ceiling or in-wall left and right speakers to the BAS, which will directs the higher frequencies to your other (satellite) speakers while the BAS handles the lower frequencies. By selecting one of the three frequency settings, you can control the amount of bass that is sent to the BAS.