Yup, series tuned 6th. The rear chamber(s) are tuned to your low frequency cutoff (the start of the passband), and the front chamber is tuned to the high frequency cutoff (the end of the passband). That's a very rough explanation of them.
Just like a ported box, if you're using two separate chambers you can't divide port length while keeping the same port area. I have a feeling based on your drawing that you have waaay too much rear port area. It only needs to be 5-10 in^2/ft^3.