Dang, you're insane dude - that sucks about the driver. Looking forward to the pics.

Btw, here's the force numbers run at 4000W and 12000W at 63Hz where your impedance is ~4ohm and the phase is 0 (so we're talking real power):

4000W = 31A = 230 lbf (160 lbf with 70% Bl)

12000W = 54A = 400 lbf (280 lbf with 70% Bl)

Btw, that's the accelerating force - Your moving mass is roughly 1lb, and at 63Hz, the amount of acceleration being imparted to the moving mass follows this equation:

So the peak acceleration is (63)^2 x displacement (units = in/s^2). With 400W, your simulation is claiming about 0.75in excursion (20mm) at 60Hz (using Akabak model).

Converting between lbf and lbm:

We have lbf (moving mass) = 1lbm * 63^2 x 0.75 / (32.17 * 12) = 8 lbf. That means the minimum air load is somewhere in the ballpark of (160 - 8) / 260 sq in = 0.6psi (166dBspl)

At 12000W, the excursion is ~1.7x greater, so you're looking at ~13 lbf for the moving mass. That means the max possible air load should be less than 1.5psi (174dBspl).

Now let's take into account the suspension compliance (which is 0.01 in / lbf). For an excursion of 0.75", the force used up is 75 lbf. That reduces to (160 - 75 - 8)/260sq in = 0.3psi (160dBspl).

At 12000W you're looking at (400 - 127 - 13)/260 = 1 psi (170dBspl)

At those SPL's, it would be interesting to run these numbers:

http://books.google.com/books?id=b_wxNccLhXoC&lpg=PA90&ots=Kg5gbKvL8N&dq=beranek%20horn%20throat%20distortion&pg=PA91#v=twopage&q&f=true
Not sure if you can apply the Fc concept to the tapped horn or not...I think using the tapped horn Fc would give an idea of the minimum distortion level possible.

Using this calculator, I'm figuring at least 400 acoustic watts in the throat with 4000W input:

http://www.sengpielaudio.com/calculator-soundlevel.htm
(multiply by the 0.04 sq m of the throat)

So 1.76 sqrt(400) x (63 / 30) / 100 = 0.7% THD with 160dBspl in the throat.

With 12000W and 170dBspl, it's more like 2.3% THD.

(That's actually quite surprising to be honest, but I guess that's just the nature of low bandwidth horns).

When you break it all down, the air should represent somewhere between 48% and 65% of the load at the SPLs you were pushing...probably slightly less since the suspension isn't linear either. I wonder if they build in a 2x to 3x strength factor on the diaphragms? I would imagine that they'd design the cone to be stiff enough to clip hard into the limiting region of the suspension - so how much stiffness is left over when adding the air load?

As a side point, if the air load ever goes away, then all of that motor force turns into diaphragm motion and your excursions will be way higher. So either you end up with way more SPL or the electrical impedance will be rising (or you get into the power factor stuff)....we're not seeing that happen with the measured impedance. I do think it is interesting to note however that the air load across the diaphragm does change with time as a function of the propagation distances through the cabinet.

So ya, I'm still not seeing any way around the fact that there are extreme pressures inside the cabinet. Maybe we should find a mic that will measure the actual pressure across the diaphragm and take all the guess work out? If that's something you'd want to try, then I can talk to our mic guys at work to see if they can't put together something real quick like. We'd want the mic diaphragm exposed to both sides of the baffle, so there'd need to be room for a small hole through the baffle.

Btw, how much is the recone kit?