Like I said, the article tells us all we need to know. To your reply, it also shows us 20%thd at that level, and thd goes off the charts below 16hz, where output drops like a rock below 25hz in sustained output tests.
If the sub can actually do it, why would you even want to? Thankfully there is a high and low pass filter knob on this sub, as you will most certainly be needing both, as it appears to be more of a wide-band-pass design, than anything else. A good entry, in that space.