Putting ports on the bottom questions

[Bill Hughes]

A round port has the LEAST FRICTION for a given area, thus less air noise. Grille cloth over ports makes noise.

Ports on the back work better because you dont hear the edge noise. Ports low and near the floor couple to the room better.

 

[warx]

Bringing this topic up again as I am looking at the UpShot cab which looks like a 4" round hole/port, no-flare and given it's only 6" total in height it must use the floor/bottom of box interaction for the oscillating air volume. (right? There can't be room inside for port length given the magnet is right there).

I love this design and I am going to do-over my 1x10 (Beyma) using half a 12x12" dia. 6-ply maple drum shell I have. Given the round shape there's no need for side bracing - just brace the back. Could even vary the port length by varying the three rubber feet height. Plus (bonus!) with three feet it's always standing stable...

Anyways, now back to the volume calculation @DukeLeJeune eludes to above; I guess this radiated mass will act as if in a tapered port. It's just hard to consider the progressively slower/lesser movement of the air toward the outside.
Volume: 580 cu.in (12" dia. x 6" minus 5.3mm ply)
4" dia. port -> length 24" tuned at 60Hz
Typical foot height 0.82", inner port hole 4", exterior: 12"
port hole area: 4" dia = 12.56 sq.in.
beginning (inner) area: 12.5" x 0.82" = 10.25 sq.in
ending (exterior) area: 37.7" x 0.82" = 30.91 sq.in
That's quite a taper... 3x the area from one end to the other (air speed 3x less). How do I determine the sprung mass of that?! Helmholtz not working here.