Actual correct answer, hopefully it entitles me to a box design..
It's because when people are willing to do a 4th order bandpass they realize they need to give up SPACE..
When people talk about ported boxes and def sealed they are always looking to save space. Sure that 15 works GREAT in 3cubes net.. It's tuned low, go ahead and use skimpy port area....
As soon as you start talking 4th and 6th order you start hearing about how ungodly big they need to be. Part of that is the extra displacements offered by the sealed or other ported section, but MOST of it is because people are finally willing to give subwoofers the space they deserve.
Instead of trying to cram a 15 into 3 cubes they start using large port volumes and huge ports onto the ported section of the 4th order. Sure they are only fitting 2 15's in a 4th order compared to the 4 ported subs they could cram in there.. However, they are also playing flat down to 15hz with authority because they finally built something that was effecient.
People see youtube vids of a guy with 4 15's in a 4th order using 30 cubes of space and it's moving air like a freaking industrial fan off of 6k.. Then they wonder why their 4 18's in only 16 cubes tuned at 35hz with a skimpy port on 20k can't do the same thing.. HENCE.. MAGIC!
Hoffmans Iron laws rearing their head once again, but when it comes to 4th orders, priorities change.
