I asked Shane Sangster, The Home Theater Doc, for some advice on building the box and received this response. Thanks Shane!!
"I prefer sealed and this driver will work either way.... obviously more output via ported, but it can still shake the walls with it sealed.
This driver moves a LOT of air. So you need to build a tough box. I used double and triple MDF for my sub cabinets. Front panel was 2.5" thick on my designs, but a lot of that was due to wanting to recess the driver a bit. box within a box with sand is a bit overboard. If the walls are thick enough and you use enough braces, that should be fine. not to say it wouldn't be better to go to the extremes. I'm just not sure it will help enough to offset the effort involved.
You'll likely want a bit bigger than 3.6 cubic feet... when you do the T/S parameter measurements on the actual drivers, the Vas is much higher than spec.... and Qts is higher as well which allows you to go bigger to get leaner less boomy bottom end. The plate amp does have a boost circuit for 25Hz which comes in handy.
You're going to wire it so it's a 5.6 ohm hookup (i.e. all voice coils in series with one another). That will work best with his plate amp.
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Shane Sangster
The Home Theater Doctor "
We should characterize the driver with the Woofer Tester to make sure the Thiele Small specs are correct. But in the end, if we go with a sealed box, they are less critical, as long as the minimum volume of 34 liters is met.
I did some simple simulations with the published driver specs and
WinISD speaker software. 60liters is near the point of diminishing returns on bass extension. Carl likes optimizing to the point of diminishing returns, so that will be the target area for volume. Driver specs are not likely to vary too much from the specs, and Volume is the only variable with a sealed box, so hopefully that part will be fairly straightforward. But that's why I'm seeking advice and corrections for my assumptions... and just to have some fun sharing...