As of now, I've got a SAZ-2500D and the electrical to back it up, so it's time to get a new sub to be powered! Here's my dilemma: I've always had 15's and experimented thoroughly with them in my car, but I feel as though it would be fun to venture into the world of 18's. However, I can only get up to about 5-5.5 cu. ft. net in my trunk. I would put the 15" in about 4.5 cu. ft. tuned to around 30 Hz. This has shown to provide a fairly non-peaky curve in my car, while being efficient and very, ver