The taller the better for an 8"driver, I imagine.Below is the image of one that is 72" overall.
I have another (harder to grab) that's 74" so both are
pretty close. The problem with one of these is that
the driver used has been discontinued.
I also have considered the ide aof mounting the driver on the
slant side and using an angled piece at the port terminus... or
a curved piece which is bent and snapped into place.
Driver mounting should be at 40" for the 74" design,
but if mounted on the slant side, other factors may apply.
A recent _audioXpress_ has a series on why the front
pf speaks should be slanted, so I wanted to apply the concept
to the Voigt and do both techniques at once. I don't know
if this is a good idea but they seemed to go together.