I couldn't resist joining up and throwing in my 2 cents.
Sounds like you've found another approach to the design here with some input from this fine forum
The approach being discussed here, is traditional vented but with ultra low tuning, which moves the peak air velocity of the system down below your intended passband. There is nothing wrong with that, though doing so is a sacrifice to maximum SPL and distortion levels for a given drive level. Originally we discussed 25hz extension, putting the priority on music over movies.
[for others here, I'm the goofball that came up with the transmission line idea that Jim posted in post #21 here]
The TL is a more complicated build, but has a few benefits over the "under-tuned" vented design being considered [compared to suggestion in post #6].
- ~3dB better efficiency through the desired passband. (previously discussed as ~25-80hz)
- 100% linearity at over 500W, The vented system looses linearity above ~350W.
- 70% BL Xmax occurs at ~600W in the vented, over 1000W in the TL.
- Peak air velocity at 500W is only ~6m/s.
The result of all that, is about an average 5-6dB better dynamic reach on paper, and reduced distortion for equal listening levels within the desired passband.
Whether or not that is worth the added build complication and the sacrifice of <25hz loading is up to you...
If you do want to go with a simpler ultra-low-tuned vented design, I would consider around 70 liters of chamber space (after losses to bracing and driver displacement) and a slot vent of 2"x15.5" x ~70" long (folded to fit). [see attachments for simulation @500W]... taking some time to simply sand or grind some smooth transitions around the bends and at the port opening would kill some of that peak in air velocity and more or less kill most if not all port noise...