Sounds like like paradise
Only a horn guy would say “just” 
Would you need 2 of them?
Just the one. So it would be two drivers opposing each other in the one cabinet, something like this:
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2x 18" 
Big subs are a young man’s game!
Says me who has a portable Lab12 TH at 38" X 30" X 14".
I must SIM those 2x18" driver ‘baby’ subs..
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Must be isobaric.
Expect some serious Xmax (cone deflection), but the right drivers are built to take that.
Can you feel your chest / stomach / gut wrenching depending on frequency 
That’s not isobaric.
Mine are 33" x 24" x 44".
One 18" driver.
There are two of them.
Indeed, opposing drivers, supposed to be good for stopping cabinet vibration. Although obviously a power draw so chunky amplifier required
Shows what I know about sealed 2 driver subs😂
Spent all my time in single driver Tapped Horn land.
Would you have the two drivers in or out of phase?
Whenever I look at sealed subs the SPL per watt around 30 to 40Hz is disappointing.
I guess they EQ them and then pour in big watts!
Reflex gives 10dB / watt more but is probably not fast enough.
Hence Tapped Horns..
In phase if you actually want any spl.
I was going to say the clue is in the title with the opposing bit. So both drivers pushing out at the same time in phase.
If you turn one of the drivers round, so its magnet is outside the box, and then drive them out of (electrical) phase you still get both pushing air out at the same time and in at the same time. So plenty of sound. But even order distortion caused by the cone moving differently on its way in compared with on its way out will cancel. There’s a Linkwitz dipole sub which makes use of that.
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@dom; hi, my first post on this forum which I joined specifically because I too intend to build JW’s JMOD v2 and Steve mentioned you already started down that track.
So my first question; what is your plan for cutting / constructing the horns ?
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Surely A driver the right way out of phase, and a driver facing backwards in phase, produce the same result? No? One goes out, one goes in, the orientation of the driver doesn’t change the relative relationship of cone direction, pressure in the box or ultimate SPL
Words can quickly get us mixed up. A picture makes it clear. This one is modified from the first pic of the Linkwitz dipole woofer.
Linkwitz’s speaker is a dipole, so his ‘box’ is open i.e. it’s really just the equivalent of a flat baffle sheet.
In my pic I’ve sealed the box with an additional rectangle of plywood, coloured slightly darker grey.
Let’s call the upper driver your ‘right way out of phase’ one. When I apply a signal the cone moves in i.e. towards the magnet because the driver is wired out of phase. This compresses the air inside the sealed box.
Let’s call the lower driver your ‘driver facing backwards in phase’ one. When I apply a signal the cone moves away from the magnet, because the driver’s wired in phase. But because the driver is outside the box this also compresses the air inside the sealed box. So the two drivers are reinforcing each other’s action. They both compress the air in the box on one half of the audio cycle and they both compress the air in the room on the other half.
But you can see that when one cone is moving towards its magnet the other cone is moving away from its. So each half of the cycle is the same (one going towards and one going away) which is to say no even order distortion.
You might not believe me. I’m just some bloke on the internet. But Siegfried Linkwitz was really smart. He wasn’t wrong about this.
I just don’t get why the driver has to be backwards here. The Sonos sub employs a design that feels a bit like this, where two drivers face each other towards the centre of an “O” shape.
Surely turning the driver with its magnet facing the wrong way so that that two driver dust caps face each other and both drivers in phase would produce the exact same result?
I’ll digest more tomorrow… it’s late 