m5james, have you looked at the ID10 sub from image dynamics (or better yet, the IDQ10v3?

I'm trying to figure out how to squeeze a 10 inch sub into the stock enclosure without doing too much work.

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Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual