I am going to purchase some FI subs. I am looking at 2 15's. I have been looking at the Sp415's but have been seeing alot of people have been going with the BL series. Now the BL N series is the neo mags which increase the cost. this is for my daily driver. I like my music loud. Here is some back story to where I am at. I went to a shop that took good care of me 10 years ago but all they wanted to sell me was JL audio. I think that is great equipment. Just not wanting to follow the heard. He sold me an alpine HD-137BT Head unit, 4 gauge amp wiring kit, JL 500/1, Arc Audio ARC 12d4 sub in sealed 1.25 cuft box. I have added polyfill, and had to turn up bass boost to get sub where I felt like I enjoyed it. Now I have turned bass boost down due sub noise during long low notes. My original thought was to go with 3 arc subs on a 1200.1 arc amp. However I will not be able to build the correct box and still be able to keep radius to fit those subs. SOOOO on to two subs and why I am I want the 15's. Can everyone chime in and explain what I would expect to hear in differences between these two models either the BL or the SP415's?????? As far as amp I am looking at the cresendo or sundown with power between 3500 or 5500 models??? I will be building my own enclosure by looking at the requirements for these subs It will need to be between 6-8 cuft??? depending on when I size trunk to what I can fit realistically. trunk opening is 34 inches x 15.5 inches and trunk depth is around 40 inches. This will be my first ported enclosure so port dimensions with getting it to the correct frequency have me confuse to what I need per factory specificaitons????? Any and all help would be greatly appreciated. I have been leaning towards the SP415's but after looking at cost I could save quiet a bit if I go with the BL's. Just let me know your imput will be greatly appreciated. I will make these fully loaded which ever one I choose. FYI