Creative Pebble Plus 2.1 USB-Powered Desktop Speakers with Powerful Down- Firing Subwoofer and Far-Field Drivers, Up to 8W RMS Total Power for Computer PCs and Laptops (Black) : Electronics
Front- and down-firing subwoofers -- Teufel Audio blog
Down-Firing Subwoofer - Placement and Orientation | AV Gadgets
HOW DOES IT SOUND? - Downfiring Subwoofer Build Finished! - YouTube