underseat subwoofer Kenwood KSC-SW11 (review and sound test) - YouTube
Amazon.com: PyleUsa 10-Inch Low-Profile Amplified Subwoofer System - 900 Watt Compact Enclosed Active Underseat Car Audio Subwoofer with Built in Amp, Powered Car Subwoofer w/Low & High Level Inputs - PPLBX10A :
BassPro SL2 | ["Add high-performance bass with a low-profile woofer enclosure", "Self-Powered, 8\" (200mm) low-profile under seat subwoofer system"]
Soundstream USB-10P 10 Inch Underseat Enclosed Subwoofer with Built In Amplifier - Walmart.com