Actually, the reason why horns are working so well is that they work as impedance transformers - on the acoustic side! A driver is 'born' with a natural high acoustic impedance (speaking in popular terms, we have a rather heavy diaphragm trying to move some light air), & the air's acoustic impedance is low. So the horn offers a high acoustic impedance at the throat (for the benefit of the driver), & through the length of the horn this is converted to a low acoustic impedance, at the mouth.

Closed & reflex boxes aren't very good at this transformation, sad to say, they stink - so the efficiency for them is max ~5%. But they are MUCH easier to handle when it comes to size in the bass area. The pay (again!) - bigger amps.

Btw., the LAB 12 offers very good performance in reasonably sized boxes - too bad they are not easy to get a hold on in my country.