Here's another subwoofer option for placement under the front seat. This is a 10" subwoofer with built in amp that puts out some decent bass for my listening tastes and gives me a seat massage on my daily commutes. Its still going through the break in period, but i've been really happy with it so far. Purchased this Boss unit for $136 on amazon and it had good customer reviews. fits nicely under the front seat. i removed the air duct so it lays flat, but when i did a test fit, it fit under the seat with the air duct intact. it has ajdustable subsonic filter, low pass filter, phase shift and remote level control that i mounted under my steering wheel.