Thanks for the reply. I am using Rick Schultz's article on
Alpha transmission lines as general guide. According to that piece,
I could achieve 63 hz with some polyester stuffing (which is
what I have) and an overall length of 49 in. I suppose that is a good place to start. I can always get the length down, but I wanted to make sure not to trim too much for a first fitting.

On the other hand, I'd need 70 in of length to go down to 45 Hz
and that length would be awkward.

In any case, I am at last getting to hear what all the theory
is about with a $3 driver and some plumbing parts. At some point
I'm going to want to push some big band music through them. Anyone
know where I can get a good recording of Ted Heath's version of
"Love For Sale?"