Pioneer UD-SW300D Single down-firing sealed enclosure for 12" shallow sub at Crutchfield
Down Firing VS Front Firing Subwoofers (What REALLY Matters!!) - YouTube
KICKER CompRT Down-Firing 8” Dual-Voice-Coil 2-Ohm Loaded Subwoofer Enclosure Black 48TRTP82 - Best Buy
Kicker 48CDF104 Comp Series sealed down-firing enclosure with 10" 4-ohm subwoofer at Crutchfield
PowerBass PS-ADF110T Compact downfiring 175-watt powered enclosure with 10" subwoofer at Crutchfield
Kicker 48TRTP102 TRTP 10-inch Thin Down Firing Subwoofer and Passive Radiator Enclosure, 2-Ohm - Creative Audio
Front- and down-firing subwoofers -- Teufel Audio blog
KICKER COMPRT10" Down-Firing Enclosure - AudioWorks of Delaware | Turn It On! | Car Alarms - Remote Starters - Audio Systems - Navigation Systems - Multimedia Systems - Custom Car Rims & Tires - On-site Company Fleet Services