Here is a small but quite powerful 8 inch sub. It was designed by none other than the famed Bob Carver. It has a 1,000 watt amp inside. The driver itself is designed to run efficiently due to it's way oversized magnet structure & long travel. Here the small diameter of the subwoofer actually helps as it works with the oversize magnet structure to limit the current needed to drive it. The flip side though is it needs lots of voltage which is provided by the highly efficient tracking power supplied class AB amp inside which they call the tracking down converter amp.
While the sub only weighs 28 pounds at least half of that weight is from the magnet structure. Low frequency cutoff is 22Hz which is very low for such a small woofer but believe me it is capable due to it's exceptionally long travel.