The EV MTL-1x is well-regarded as a good "PA" sub. Maybe it's good for live sound reinforcement, but it's awful for recorded music, ala DJ's spinning.
I thought I recalled being disappointed south of 45Hz, but it looks more like 55Hz from EV's published response plot for these. (attached, if I can do so with a post count of TWO.)
While there are few ways to make live sound south of 60Hz, (harmonics of a bass guitar, pipe organs, synth bass are clear exceptions,) playing recorded music, in a DJ setting, calls for the same class of gear we enjoy at home... just able to play much louder. I see no reason why a great design like the T-6, which makes the most of a single sheet of wood, and a class of driver that's readily available, cheap, and handles huge power (relatively speaking) can't make an excellent "PA" sub for DJ'ed music.
Four of these cabinets, given thermal and excursion limits, seems to blow even a pair of EV MTL-1x cabinets, (which I can't fit into the corner I need to fill,) out of the water, while extending usefully 25Hz farther south. Instead of driving a single cabinet with TWO nice Crown MA2402's bridged mono, (1600W at 8ohms to each driver,) I'll use one amp to drive all 4 cabinets, (800W at 8ohms for each pair,) cranking out the same SPL, with MUCH lower extension. If I fry drivers, I'll replace, or even recone them... I'm still waiting for an answer from Fi about what re-coning costs for these, their cheapest product. (BTW, while these amps are capable of driving a lower impedance load, with more power, listening proved they sounded best with an easy 8ohm load. Damping factor increase responsible?)
An added benefit to likmike's T-6 design, using the side-mouth variant, is that the gang of 4 cabinets fits into a very small space (72h x 48w x as shallow as possible... 12-13in) under existing flown cabinets, and allows all 4 mouths to be ganged together at gut-height for woofer surfing, a popular sport on any club dance floor.
Again, these seem to offer a very good compromise of low build effort, low extension, max output, efficiency, value. I've been trying to fill this magic corner, (in which I'll also experiment with corner-loading, but this doesn't offer much "surfing" potential,) for 6 months, and this is the first design where I could achieve the SPL I'm looking for in the alotted corner space within a reasonable budget. Just like Danley designs his cabinets to be an integer divisor of a semi truck load for efficient transportation between gigs, a stack of 4 of these T-6 cabinets fills my corner perfectly, with no wasted space. Plenty of other designs discussed here, and on other DIY forums looked great, but I couldn't fit enough of them in this corner to fulfill my design goals. (I even considered stacking 8-9 Insubnia Anarchy boxes!)
4 of these, built with the Fi X10, model with an efficiency of about 97dB/1W, which pretty much exactly matches my top boxes.
I've yet to find anyone back the idea up with a credible study, but "rumor" has it that juicy sub-bass, south of 50Hz, makes bar patrons want to drink more, whereas sparking highs make bar patrons want to urinate more. Our top boxes run out of gas at 16khz, and I'm fine with that
The last benefit of this experiment is that if they don't work out at the club, just like a retired draft animal, these will find their way home to pasture, where they can retire comfortably on a diet of mildly-amplified vinyl, and the occasional action movie.