I've been watching the BIB (Bigger is Better) project developments
at the full range driver sites. Terry Cain put up a design at
Full Range Driver Forum from some Japanese manuals quite a while
back. Now there is renewed interest in this folded pipe that
rear fires out the top instead of the bottom. Corner loading
is all-important in this build.
Other thing is an unique PVC application that I posted in
single driver forum here on building a Nautilus style t-line.
See subject line: "I wish I would have thought of this."