Hello, At the moment I have 2 Kenwood 12's and a (currently not working) Alpine 500 watt amp. Instead of replacing the amp with the same one, I'm going to sell my subs and get a whole new system I wanted to hear what you all had to say before I make any decisions.
First, what are the differences between 1 18" sub, and 1 15" sub? (assuming they are the same brand/model. for ex. 1 Fi 15"BTL vs 1 18"BTL). Which is lower etc. Would I be better off with 2 lower quality 15's than 1 high quality sub in terms of SPL (2 AQ 15" street duty's vs 1 HDC3 15"?
Right now, I'm looking at either 1 15" AQ with an MB Quart DSC2000.1D or 1 Fi 15" BL (maybe BTL) with the same amp. Which would produce the best lows, and pound the hardest?
My goal is the loudest, lowest system I can get for ~$500-600.
I have a 2000 crown vic police interceptor, so trunk space isn't an issue, and I'll be building the box myself.
Being such a large vehicle I would say go with 2 15" woofers or 1 18". The subs you go with do make a difference but what makes the main difference is your box. I'm not a pro at what size for what type of output, however, I do know that building a box to what you are looking for is key to making these subs be "loud", reaching their potential and getting what you're looking for out of them. I'd say go with the BL series, the BTL is a SPL sub, the BL will be a more all around sub. If all you want to do is pound, one 18" BTL in the correct ported enclosure would do nicely. If you wanted a little more SQ (I know they're not "SQ" subs) out of your system, 2 15" BLs in a ported enclosure would be better. You may even look into getting a 2500 rms amp to run to these BLs. Your electrical may need to be upgraded though to go that high in rms.
I wanted to hear what you all had to say before I make any decisions. 
