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, very low. Now, if I stuff an 18" in 5.5 cu. ft. and tune it to 30-32 Hz, will this make it significantly peakier? Will the lows be better or worse? Do you think it would be louder (perceptively) or not? Thanks for the opinions.

Goals - loud daily driver with excellent low (25-35 Hz) freq response, while not sounds like complete crap (never been into the whole ProBox thing)

Any opinions?

Low's would most likely suffer, unless you have huge power to back up the woofer. As Hoffman's iron law goes, Efficient enclosure, low frequency extension, or small space, pick two.

Try to get a 15" BTL,enlosure designed to 5-5.5 cubic feet tuned @32hz, im tuned at 32 hz (18" N2 BTL,7.5 cubic feet after displacement in a yukon xl) It hits the lows well and still sounds good with reggae,and alternative rock music.

Ok I'll just stick with the 15". I'm more familiar with designing a box around that size subwoofer anyways. Thanks y'all.

That's unfortunate about not being able to fit the 18"

on a side note, there has been tons of Grand Prix builds lately! Or is that just me?