I'm looking into buying a Soundstream xxx18 and i have a few questions. First of all, here are the specs from the website.  SPL Tuned Enclosure  XXX-18  Min. Vented (ft.3)  4.00  Port (dia. x length)  (4) 4x15  Fb (Hz)  49.91  F3 (Hz)  43.54  Opt. Vented (ft.3)  6.00  Port (dia. x length)  (3) 6x13.5  Fb (Hz)  50.00  F3 (Hz)  42.71  Max. Vented (ft.3)  8.00  Port (dia. x length)  (4) 6x12  Fb (Hz)  49.84  F3 (Hz)  42.24  Low Tuned Enclosure  XXX-18  Min. Vented (ft.3) 4.00  Port (dia. x length)  (3)4x18  Fb (Hz)  39.97  F3 (Hz)  36.81  Opt. Vented (ft.3) 6.00  Port (dia. x length)  (2)6x22  Fb (Hz) 35.00  F3 (Hz) 32.18  Max. Vented (ft.3)  8.00  Port (dia. x length)  (2)6x20.25  Fb (Hz)  30.02  F3 (Hz)  27.96  What is the difference between a SPL tuned enclosure and a low tuned enclosure? im not planning on doing and competitions at this point. i just want it to slam and slam hard. I drive and 06 Ford Taurus at the moment. (Hoping to get a Blazer soon) So all i have is the trunk room to work with. i have a kicker L5 15" in there right now. I will measure the trunk tomorrow and post that on here. Also, what is the difference between the Fb (Hz) and the F3 (Hz) the numbers are relatively close so i dont know if i matters or not. Please help me!! Thank You