If your question about frequency response for a sub going to 1KHz, are you referring to the Eminence Delta or the Ultimax? If so, you aren't considering the fact that it was never designed for home use and it's definitely not designed to be used as a subwoofer. Does it produce notes that fall in the range of a sub? Under the right circumstances, definitely. Will it happen in a small enclosure? Absolutely not, unless it uses a long, large diameter vent and the signal going to it is limited. This driver is geared toward guitar and bass players who need mid-range, as well. Stick this in a sealed 4-12 cabinet and it works great for a Marshall head OR a bass because A) a Marshall head doesn't produce a lot of bass and B) four drivers in that arrangement act like a larger diaphragm.
This is about the Delta Pro12a right? If so, look at the attachment and you'll see that they handle a fair amount of power, but not if the tuning and box aren't right.
https://www.eminence.com/pdf/Delta_Pro_12A_cab.pdf
Some people are obsessed with hitting the lowest frequencies- I think they may come from car audio, but that's not the same listening or acoustical environment, by any stretch of the imagination. Most music and sound tracks don't use anything below 20Hz but it's a good number to use as a lower goal because that's one of the the theoretical limits of human hearing.
Something you might like to know- bass players blow speakers more often because they don't understand what is being sent to them than because of high power. In fact, some bass amplifiers have a built-in HP filter at about 35Hz specifically because it's possible to produce frequencies in the sub-20Hz range, even if the instrument's tuning isn't that low. If you have heard of 'beat frequency', this is the reason- play two notes that are close together and you can produce not only the intended notes, you can also produce the sum and difference frequencies which, if the original notes are G (on the E string) and A (open A string), the difference is 6Hz and a lot of people use the beat frequency to tune their instruments. A member of a bass player's forum is also an Electrical Engineer and he offers a product that connects between the instrument and the effects and amp- it filters sub-35Hz frequencies at a steep slope in order to allow himself (originally) to play at high SPL without puking his speakers and when others heard the difference (actually, there's no difference, other than the amplifier and speakers being happier) and saw that the cone's excursion was greatly reduced, he started to receive orders. Many people who design speaker enclosures ignore the fact that below the port tuning frequency, the woofer isn't controlled well, if at all.