I saw one sub designer’s quip: "A fast woofer is a tweeter". Fast in regards to a woofer is not used literally, but to it’s perceived lack of boom. Many factors contribute to boom, mostly the room. But Arnie Nudell didn’t employ servo-feedback woofers in his IRS, RS-1b, and other speakers for marketing reasons, and neither does Brian Ding in his Rythmik subs. Nor does Richard Vandersteen employ feed-forward in his for no good reason.
If you want to see the woofer that hardcore home theater DIY’ers have for years put in their subs, check out the TC Sounds LMS Ultra 5400 18" woofer. When last available (from Parts Express) it was $900-$1000 for just the driver. Insane motor (magnet structure), extremely high excursion (2"!) and SPL capability.