The DSR-100 system is a 4.1 speaker system, consisting of independent left and right front and rear surround speakers coupled with a subwoofer designed to extend the low end frequency response of the entire package. While Logitech employed the traditional plastic enclosures for the satellite speakers, they have used an extruded aluminum enclosure for the subwoofer, which also houses the amplifier and power supply. This definitely adds mass to the subwoofer enclosure and allows for the driver to get down to work moving air instead of flexing a plastic enclosure.