Back in the 70s my dad knew a bass player who used the classic Bose cabinet with lots of small speakers - firing from the back, IIRC.

The bass player from Spyrogyra used to endorse Bose as well. I'm trying to remember if the whole band wasn't going thru them in the ads (yeah, it's gotta be real! It's in a PICTURE! - lol)
 
Mike

I'm also intrigued - the usual tuned port in a bass reflex cab is a plastic tube, so why can't those 'curtains' of the Karlson box be made out of plastic too? I can see how it works if they are part of the structure, but why would they need to be?

They could be.  In fact, the Karlson hobbyist/fanatic website (http://home.planet.nl/~ulfman/)used to have an article with plans so you can make a Karlson stereo speaker from cardboard.