The folded horn technology is used to provide the longest horn possible in the smallest package to produce the deepest bass as well as increased efficiency and directivity. For low frequency reproduction these speakers are typical a 15″ for the small subs, a 18″ for the medium size subs and then the monster 21″ for largest subs.
All of the technology of this site addresses commercial applications to improve that overall efficiency of the speaker cabinet which in turn reduces that power requirements to get the same sound pressure level at a given distance.
These speaker designs will produce frequencies down to 40 Hz and are used for subwoofer applications that cover ranges up to 200 Hz. The subwoofer application recommended crossover point is 80 to 120 Hz.