[see link]

After building kits, I cobbled together a variation on the
PVC Periscope below. My pair use a few more couplings and
are longer in pipe length but here's the start of the idea.

I tried out a test sample using the 49 centers but
I think I'll stick with my $3 Radio Shack 1197's. It's still
one of the best builds I ever heard.

• PVC pipe speakers at Full Range Driver Forum