Funny, they claim 12 Hz for the 46 lbs ForceField 5, and then link to a review where the measurements say:
The ForceField 5’s close-miked response, normalized to the level at 80 Hz, indicates that the lower –3-dB point is at 24 Hz and the –6-dB point is at 21 Hz.
When you look at the graph, you see a bump around 60 Hz and the 25-40 Hz response is a plateau 5 dB below that peak. They must disregard the 60 Hz bump to read 21 Hz at -6 dB. In any case, it's already 10 dB down at 20 Hz so forget about 12 Hz.