To address some of the confusion regarding comparisons, audibility and power:
First, Brandon's room is in a basement that's 100% masonry walls and 50% underground. He enjoys a MUCH lower transmission loss factor than you'll see in most rooms. Sorry we didn't have the time to run a room gain profile because Paul and I were there for just the day and we tried our best to keep out of the way of the auditions of the speakers and subs and amps available, but trust me... Brandon gets to keep the vast majority of sound waves his system generates. I'm envious of that as my room suffers a huge amount of transmission loss on the low end.
If you step out the back door into his back yard and close the door behind you, you'll have no idea of the mayhem happening on the other side of the door. To contrast that, my neighbors 200 feet away, sitting in their living rooms, look at each other, roll their eyes and say "Dave is watching a movie tonight".
That's the 1st point here; instead of pushing the system to get more, the system pushes you with far less input. That's a BIG factor.
Second, When you have a 12 or 13L driver in a room like that pumping 7 Hz transients at reference levels +, it's not "audible", but it's definitely easy to perceive. When <15 Hz events occurred, you saw attendees immediately run to the laptop location asking "What did THAT hit?", "How low was THAT one?" I actually pressed my hand to the concrete slab floor and felt the effects in the slab (contrary to the conventional wisdom on the subject) and I stood on the overbuilt riser and felt even more. Standing near any boundary added around 6dBSPL and the suspended ceiling (and anything not welded or bolted to the structural members) had no chance to offer resistance to vibrations. That goes to the entire house all the way to the attic. I walked around the 1st floor while the demos were going on and the house was in spasm, making sounds that were hard to recognize. I actually feel sorry for folks who claim they can't "hear" those events in music and soundtracks. For me, it's unmistakable and the evidence was that the same holds true for those who rushed to see the SpecLab result.
Soon after SL was up and scrolling, someone asked Paul "What the heck is that, it's all the way down to 1 Hz?" He explained that it was the mic picking up people walking around upstairs and running up and down the basement stairs. It even picks up someone plopping down into one of the seats on the riser. <10 Hz is all around us all the time, just not at the levels we experienced at the meet. It's not audible per se but is perceived by combinations of other senses and its effect on surrounding fixtures. When you bump the levels down there via multiples or different drivers, the perception rises by magnitudes.
If it were the result of THD, the harmonics added would be easily visible in the SL graphs vs the digital versions. The THD from all 3 systems, at the seats, was extremely low to non-existent.
Third, the power required, because of the subject mentioned above in the first point, is far less than what it takes, say, in my room. Again, Paul has a Fluke multi that will measure micro volt peaks and he wanted to test the voltage the drivers were seeing (and amps via Ohm's Law, because of the very low impedances seen by the amps) but, Paul is new to the forums thing and preferred to go with the flow vs stepping in to direct the flow of events. Again, I don't think watts was the problem at all. I think current draw is what shut down the amps with the 1.68 ohms at 4 Hz transients kinda demand that was occurring regularly throughout the demos. The situation with the 24" wired 2 ohms/ch in combination with the source demand was probably asking the amps to pull more than 30 amps from the wall for milliseconds transients... repeatedly, until they just had to go into over current and/or thermal protect. My opinion, FWIW.
Fourth, the few times we heard a clack-like sound, IMO, was not the driver, but the amps choking before protect circuits kicked in. I don't believe the 24 was moving anywhere near its 'clack point'.
Fifth, although Brandon deserves credit for the speed and accuracy with which he threw the 16 cubes box together for the 24 in record time (he's really quite the woodworker, looking at his other various projects), the box was nowhere near built to handle the driver. As a result, a lot of its energy was being sucked out through rather violent vibration on all panels, vs, say, his dual-opposed 18 stacks, which are quite inert in comparison when pounding away.
In the end, take any single driver you know of and hand it over to the GTG maniacs and they'll hand it back to you in a coffin. The 24 not only lived through that experience, it sounded sweet as honey in the process. I explain any and all shortcomings as listed above and have the driver at the bottom of the list of possible reasons. If that don't say it all for the driver, I dunno what will.