AS my monicker suggests,I've owned horns for a long spell!
Beginning with Klipschorns in 1981, then the Duos (as string starter) 20 years later, though, as someone points out, the Duos' bass isa powered direct driver, not a horn.
I recall pictures of people maiking a bass horn that ran from their garden into a bay window, so one can see getting a REAL bass horn involves SPACE!
Simple law of physics.
It's far too far into my past to recall just how 'good' the Ks were, but I have fond memories of them, flawed though they might be.
They had a life-size sound, as much as anything making 'normal' boxes sound just that - boxes.
I'd love to have had mine 'improved' by the Volti upgrades.
As to amplification, I did run mine initially with a Hafler DH200 which is in theory overkill, but ,like horsepower in a car, it gives you more power, which in hifi means faster rise time?
Switching to DNM amp gave me more depth.
Though a Son of T chip amp did surprisingly well too!