If the 2x 6.5-inch woofers have an Xmax of 5 mm, then that figure of 80 dB at 20 Hz at 1 m seems to be quite reasonable and achievable.I asked KEF for a more specific metric, the maximum anechoic SPL achievable at 20Hz, and they said 80dB. In-room that'll be a lot louder. I still think it's impressive, but much more believable for 2x 6.5-inch woofers. Besides, it all depends on what the bass limiting curves look like. Maybe it can get to 100dB at 30Hz, for example. We'll have to get measurements to see.
If the 2x 6.5-inch woofers have an Xmax of 5 mm, then that figure of 80 dB at 20 Hz at 1 m seems to be quite reasonable and achievable.
With the same Xmax of 5 mm applied to a response at 30 Hz, we can get to only 87 dB, not 100 dB, unfortunately. Sound pressure goes up as the square of the frequency ratio, so we get an increase of 2*20*log10(30/20) = 7.0 dB.
Commensurately, at 11 Hz the maximum output level will be around 70 dB. By 50 Hz we get to 96 dB, and 105 dB is reached at 85 Hz.
For a subwoofer with 2x 6.5-inch drivers, to produce 105 dB SPL at 11 Hz at 1 m would require an Xmax of about 300 mm. As this is about the same order as the enclosure dimensions, then I doubt that it is feasible for it to do so.
Alas, you have been a victim of smoke and mirrors--KEF never claimed it puts out 105dB at 11 Hz. No! They claimed a peak output of 105dB on one line and a frequency response on another line--they never, in any shape or form claimed the two specs are related to each other.
Basically, it is a 18" PA woofer in a 6.75 cubic foot box
There is nothing physics defying about it, no magic, no messiah has come down from the clouds to alter Hoffman's Iron Law--just parametric EQ boost and dynamic frequency limiters
So yeah, I find what KEF is doing is laughable--but they need to make a profit so give incomplete, misleading specs--like audio gear on Alibaba.
They are selling to specific groups, the people that want a tiny, sexy little sub to match the room decor,
Granted, anyone that knows/understands acoustics won't buy such a thing.
They...now are angling to go full lifestyle.
Makes sense, they went bust in 1992 and was purchased by a China based company... sooo... yeah.
and basically every other speaker company.