so i have a newer car, a 2010 audi a4 that i am looking to purchase a sub for. i have a company making me a fiberglass box for an 8 inch sub that will fit in the side pocket of my car so i retain the entire trunk and access to the spare.
i have a pre 2010 alpine mrp-450 mono amp that i am planning to power the sub with. i have been out of the car audio game for a solid 4-5 years at this point, so i am looking for some help on an 8 inch sub.

looking for clean bass, not loud bass. i have a bang and olufsen audio system stock and plan on using a JBL MS-8 processor to give a good clean signal to the amp. only variable left is the sub itself. i have roughly $300 to spend, but would rather be around 200 if possible.

lets see what you gents can come up with. a 10 inch is also a possibility provided it will be a clean sound.

whats the mounting depth of that box and its cubic feet?

still waiting on specs back from the company, but its a deep pocket. i'm not too worried about a lengthy woofer.

.cu will depend on the woofer i select. i can have the box made specific to a woofers specs

well as far as 8 inch subs go i'd probably go with http://store.soundsolutionsaudio.com/products/sundown-audio-sa-8v-2-600w-sa-series.html

assuming you have at least 1 cubic foot of box space.

you'll want the dual 4 ohm version.