Can a large sonotube be sealed and be just as effective as a braced box?That is the way Internet forums work. If you want a plethora of opinions, none of them the same, just ask in an Internet forum. :laugh:
If it were me, I'd just build a big sealed 21". Ignore the people saying you could get more output. The sealed 21" has PLENTY of output and it goes smooth and deep. I love sealed subs but you need a lot of swept volume for them to work well for HT. The smaller drivers NEED to be ported, to give the extra headroom. The 21" has an abundance of output, without the need of porting. It goes subsonic with ease because you don't have the roll-off under the port tuning. It sounds awesome.....