To get down right technical, as drawn.
4.02 cubes
23.5" port length.
That gives you a tuning of 31.7 Hz
F3 of 27.4 Hz
3.8 dB gain @ 44 Hz
That includes removing the basket displacement. So this is the true figures at the end of the day.
I would shorten the port up a bit to get closer to 20" and to get that simply remove that extra piece in the rear (the 3.5" piece).
That will move the tuning up to....
4.14 cubes
20" lg port
33.3 Hz tuning
28 Hz F3
4.5 dB gain @ 44 hz
Up to you, I would opt for the extra gain and less work, lol.
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