Just a question:
Why has it to be a band-pass sub?
A band-pass has a very small frequency-band.
If you take a closed box you'd get better results from the same speaker-chassis by having a smaller box,too.
I've tried both (I self-built some calculated band-pass boxes) but I ended up with a small closed box and I'm very pleased with it.
Just a thought...

TeeMcBee
Got my Mk2! # 080000143
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TeeMcBee
[orange]Mk2, # 080000143, 40+30 GB, Tuner, Peugeot stalk hookup</font color=orange>