The X3’s have two woofers, the two drivers under the tweeter.
The one above the tweeter is a mid-range driver.
You probably read in the PTA review that the X3s are a 3-way speaker. That is incorrect however, they are 2.5-way, so the top most woofer does play the bass freqs. This is visible if you view the cone excursion from the side when playing a bass heavy track. My dealer also confirmed they are 2.5-ways. To the best of my knowledge, none of Børresen’s models are 3-ways, as he apparently takes issue with the phase challenges posed by such designs. Regardless, the 2.5-way X3s manage a midrange clarity that’s superior to that of most 3-ways I’ve heard and definitely better than any other speaker I’ve owned, so the fact it’s a midwoofer as opposed to a dedicated midrange makes them all the more impressive.