Lets see those subwoofer setups - BMW 3-Series (E90 E92) Forum
Basser - FBbmw09 BMW 3 E91 Touring Fit-Box subwoofer enclosure
E92 Full Bass Level One – Musicar Certified Sound
E90 Add-A-Sub Level One – Musicar Certified Sound
BMW 3 Series Sub Box BMW 3 Series Subwoofer Box E90 Sub Box E92
Car Subwoofer For Bmw F10 F30 G30 E90 Under Seat Universal Audio Music Stereo Low Range Frequency Loudspeaker Bass Speaker Horn - Multi-tone & Claxon Horns - AliExpress