Dayton Audio have just introduced this 21" "Sub" Driver. These are its specs.\n\nNow before all you sub enthusiasts drool, note that this is a highly sensitive 997db), relatively high Fs (28 Hz), low Qts (0.27) driver. So this driver is in no way suitable for a domestic sub. Note that it starts to roll of at 50 Hz. I suppose you might do a sealed alignment with massive Eq. The bass would be tight as a drum.\n\nHowever this is clearly a commercial driver. It has absolutely the perfect parameters for a massive exponential horn enclosure the size of a Kiosk to pull up the bottom end.\n\nTwo or three of these could fill a huge auditorium without breaking a sweat with awesome SQ. By the looks of the FR it looks as if it be crossed at 400 to 500 Hz range, which is perfect for an active biamped enclosure, because that is the power divide. You could couple it with a modern sectoral horn of the type JBL now specialize in. Alternatively you could top it out with a massive vertical linear array.\n\nIt almost tempts one to go looking for the right commission to design it!