Parts Express recommends a sealed cabinet of 4.18 ft³, or a vented cabinet of 11.79 ft³. Based on those two recommended sizes, I think they meant this driver to be mounted in a sealed cabinet.
A box of 4.18 ft³ becomes a box with interior dimensions of about 19.3" on each side, and 11.79 ft³ becomes about 27.3" on each side. To get those cabinet dimensions in inches, convert ft³ to inch³ and take the cube root.
You can adjust those measurements to suit your needs, as long as you end up with the recommended interior volume. You will also have to account for the volume of the driver itself (PE should tell you what that is), the interior bracing you use in your cabinet, and the outside dimensions of the port vent (if you use one). If you are using ¾" thick sheet lumber to build the cabinet, don't forget to add 1.5" to convert interior dimensions to exterior dimensions.
Most phones and computer operating systems have calculators that readily do that. I don't know if 36×36×18 works or not (exterior or interior dimensions?) but you can do that math
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PE suggested a tuning of 16 Hz for the vented cabinet, but they didn't suggest any port dimensions for that. Ask them.
