Anyway, being pretty isolated socially from any other hobbyists I have no effective gauge of what I'm hearing. The first impression I
have of making the toobz length nearly 10 ft overall is that
effective listening is put too far out. In other words, just like
my 8.5 ft straight pipe open at the front bottom, you have to get
way back in order to appreciate the lower frequency reproduction...
with considerable volume.

The folded U-shape has given the most satisfying listening
experience.

other thing to try is going in the other direction: shorter.

I will follow up with the link (when I find it) of another approach.
It'd be good if all the tubes were archived in the same place but
I guess not many are doing this kind of building.