Vibe OPTISOUND Mid Woofers Underseat Subwoofer for BMW 3 Series E90/E91/E92/E93 | eBay
BMW 3 SERIES G20 G80 M3 18+ STEALTH SUB SPEAKER ENCLOSURE BOX SOUND BASS 10 12 | eBay
Bavsound underseat subwoofer installed! - BMW M3 and BMW M4 Forum
New underseat sub option? - BMW 1 Series Coupe Forum / 1 Series Convertible Forum (1M / tii / 135i / 128i / Coupe / Cabrio / Hatchback) (BMW E82 E88 128i 130i 135i)
BMW E46 3 SERIES COUPE STEALTH SUB SPEAKER ENCLOSURE BOX SOUND BASS AUDIO 12 10 | eBay
Sound System, Subwoofer System for BMW 3-Series F30 & F80