EDIT: btw the actual volume is 1.76
You forgot to take out the volume of the external thickness of wood. It is Internal volume that you need to work out
I woked the edge of the box as 0.5" i think but cant remember also So the 8" Height i used is actually internal height so the box you make will actually be 9 1/2" tall if you use 3/4" MDF for base and lid (which i recommend as a minimum)
I have seen, installed and read post's of very similar things many many many times so sometimes you just know what kind of sub a person has and what would be best for that sub by having at least some knowledge of the TS parameters. So i can have a pretty good stab at showing you the kind of things you will need to do to make this new enclosure better than the crap prefab ones that you get with the packages.
I didnt really mean use those measurements as they were just a rough guess using the minimum TS parameters for a JBL 12" sub. Some may say the JBL sounds better than yours, but the parameters as a rule of thumb are very similar.
I dont need to know what amp you are using as that doesnt have a great deal to do with the design of the enclosure.
I am trying to give you words of wisdom about designing a round box and yes i have done it recently.
The port is very important as this will be the tuning of the box and should be designed with the box in mind. The prefab ones are well known for port noise due to increased port velocity due to port area hence why i say to use a 4" port.
No one will take a dig at your sub as its not the worst and if your happy with it then thats your perogative.