What's going on with that exposed bottom driver?
View attachment 233098
The bass system is the "Isobaric" loading in this speaker invented by Harry Olson in the '50s and used by Linn (and many others) since the 1970s.
There are 2 ways commonly used to link the 2 drivers together with Isobaric loading.
One is to have both drivers facing out of the cabinet with the inner driver loaded by the cabinet and firing into a small(ish) sub-enclosure for the outer driver. The Linn Isobaric is this type.
The other is like this, with 2 bass drivers bolted through the baffle using common bolts. The inner bass driver is mounted conventionally with the second like this. It is simpler stiffer and probably better as well because the Isobaric volume is smaller but it does mean you see the back of the outer driver unless a cover is supplied (IME it usually is)
My main speakers have 4 isobaric bass drivers mounted like this but a cover was supplied.