This is the Acoustimass 15 section, there has been III series of these, all being active bass module giving superior bass response. Improved circuitry gives better range and higher overall sound output. This is the original series Bose powered 5.1 system. Designed for medium sized rooms, good for around 100 watts per channel 8 ohms classic speakers. These have reasonable bass response and were not updated for quite some time. Still sound good if you can find a good one and don’t want extreme bass. Colour options black or white.