Check out the Earthquake SWS series.....they have the patent on this technology. I have the SWS 10 and I even auditioned it next the Pioneer and quite frankly there is no comparison. The 10" Earthquake outperforms the Pioneer all the way around.
www.earthquakesound.com
BEWARE of small boxes however! I know that they claim you can put these into dinky enclosures but if you want TRUE subwoofer performance you still need cubic inches. The nice thing about the shallow design is it offers you the ability to tuck a custom box in shallow areas where you couldnt before.
I currently have the SWS in a 1 ft^3 box for testing purposes and it absolutley scares yah! In the recommended .25 ft^3 box it was only so so. I am going to settle in on a .5 sealed as soon as I find the time to custom make one that will tuck in behind the rear seat.