Amazon.com: Alphasonik AS10DF 10" 1200 Watts 4-Ohm Down Fire Shallow Mount Flat Enclosed Sub woofer for Tight Spaces in Cars and Trucks, Slim Thin Loaded Subwoofer Air Tight Sealed Bass Enclosure :
Down-Firing vs Front-Firing Subwoofers | Klipsch
Front- and down-firing subwoofers -- Teufel Audio blog
LAB PreFab™ 0.48 ft^3 Sealed Downfire MDF Enclosure Box for Single 12" Round
Front- and down-firing subwoofers -- Teufel Audio blog