You misunderstand, it was just an example. Any good 12" sealed sub will have similar performance, within a few db. Rythmik F12, SVS SB-2000 Pro, etc. "Making things rattle" isn't a metric for performance lol. The Kef doesn't even get to 100dB at 30hz WITH Kef's(generous, most likely) assumptions of room gain, pushed to the max. That's not enough for high-level listening(say 83dBC reference) with a dynamic range of +/- 20dB. And even if it was, you don't really want to be pushing your sub to the max. It's also not even CLOSE to enough for -10dB on tv/film, which requires as much as 113dB. Sealed 8" subs don't normally have enough 20-30Hz output to even reach 80dB peak. So whatever resonant frequencies are making things rattle for you are probably much higher than that. It's a bit silly to even call them subs, they're more like midbass woofers.
Again, not saying it isn't adequate for music listening, just that no miracles are being performed here. It looks like a great product for people who are happy with the kind of bass you get from an 8" sub. I just wish it was a bit cheaper, at its price it seems really cost ineffective to buy multiple. The size is perfect for having 2-3 subs even in a small apartment. And I say that as somebody who never really had trouble finding space for a 12" sub in a 500-600sqft apartment.
Well
100dB at 20hz is 40 Phons, and this won't even do that
with room gain. So yeah, you're not going to produce meaningfully audible 15hz with this thing lol. Measurable, sure. I kind of doubt anyone looking at a KC62 cares about infrasonics, though.