Originally Posted by Mach V Dan
I replaced the underseat woofers with some Jehnerts fancy ones, and they didn't do much for me. What did help was an 8" sub that I put in one corner of the trunk in a custom box.
I did something similar. Ended up using a JL 700/5 and JL 200/2 and the technic harness and all problems are solved. JL 200/2 powered the rears and 700/5 powered the front, under seat, and trunk sub (JL 10w6v2). This is assuming that your car comes with HiFi though. I got all my stuff through MusicarNW. PM (VP Electricity) to find out more and also check out their website. You can't go wrong with his solution!
Current: 1987 E30 325is, 1997 E36 M3, 2004 E46 M3, 2015 F80 M3
Past: 2011 E92 M3, 2011 E92 335is, 2008 E90 M3, 2007 E92 335i, 1995 E36 M3