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About the 18inch i still need boot space
2 x 12'' is 24'' cone surface area, so what's the difference, the 18 would fit no worries.
It's about the same price as a single Type R, but it will make you realise what looking outside the box can get you. I've installed an IXL 10 in to an Astra, and an IXL 12 into a focus sedan, i haven't found a sub yet for similar money that competes, regardless of the application.
If the remaining two 18's are still in stock in a few months time (they probably won't be) i'll snap them up for HT duties.
Alpine has always been good for me so sticking to it might not be what use think but be s**t if we all had the same ideas.
There's only a minority of people on here who don't think Alpine is the bees knees (mainly due to the fact we are willing to trial other highly respected gear). So you have the same idea of the other idiots who waste their money on sub-par products from alpines speaker/woofer range.
No offence or anything, you just should creep outside of the box, and go with what we advise. IDMAX woofers are said to be far better than the Type X woofers, if that comparison means anything to you. You can pick them up on eBay for roughly $450 from the US. That Mach woofer will satisfy your bass needs a lot more than an Alpine unit will.
Going to be a big box in your living room, best go an IB setup through your wall into your bedroom