Just curious, why don't Axiom subs go any larger than 12"?

Probably because they opted for a smaller cone with more excursion to reduce cabinet volume and hence increase WAF and lower production and shipping costs. It's cheaper to build a higher powered amp to give more excursion than use a lower powered amp with a larger cone area. It's easier to manage distortion with a smaller diameter cone as well. Ian has always said he's sacrificed some SPL to optimize linearity. With the v4 sealed subs, he's nailed it.

Makes sense. WAF = wife acceptance factor?

If one considers all the factors, whether in a sealed or vented sub, a pair of 12's will have about the same output and extension as a single 18. It's easier to put the 12's into an elegant cabinet and it's cost effective as well.

Axiom could easily have an 18 - but when building drivers, building 2000 twelves at a time is more cost effective than building 1000 twelves and 500 eighteens.

Yes to WAF. I think a 15 or 18 would also wreck Debbie if she's still assembling the drivers.

Makes sense. An 18" cabinet looks like a euro sized washing machine.

Haha. WAF is, sadly, part of my equation. WAF = 1/(cabinet size)^X , where X = WCF (wife chill factor, lower is better)

Lol

It would be pretty neat to see what they could do.
I've been daydreaming about multiple 10 inch arrays. I seen one on tv once. 4 or was it 5 10" woofers in one large/long/short cabinet.
Been thinking about the potential ever since.
Wonder if you could fit 4 10" woofers in the EP800 and just power it with external amps.

3 would fit.
Wonder how the numbers would work on paper.
3 10's would have more suface area than 2 12's, no?
Its already a nice size cabinet. Might need to shift around internal bracing...
Wonder if one ADA 1000 would be appropriate.
Or 3 built on/in amps.
I can imagine it'll be pretty tough to improve on the EP800 though.
Do it! Do it! Do it!
Just joking.
I'll just daydream over here in the corner.
Lol.

New cabinet...long and short (vertical orientation)...
I could fit 1 with 4 10" drivers behind my seat/ below the second row.
Edit:
It would replace the 3 powered subs already there and the 8" sitting between the kids seats above them.

I could fit EP500's under the bench to FWIW.

I could fit six EP800s under the stairs, two in the shower and one in the bathtub.

That might be over kill.
Lol.

One EP800 is over-kill.

It's interesting that the top-of-the-line Bryston subs are using 8" drivers.

http://www.bryston.com/products/speakers/Model_T_Subwoofer.html

To differentiate from Axiom's. At least that's my theory.

Yep, but I haven't seen a lot of "differentiating by sucking" in their strategy so far... so they must be happy with the 8" performance.

At first glance seems like the 3x8" sub doesn't go as deep as the high end Axiom subs but that may be more a function of cabinet size than of the driver itself. The EP500 also has an 18 Hz -3dB point and that is probably closest in cabinet size.

Another angle to this is that Bryston uses 8" woofers on their T and Middle T so using the same on the subs makes good sense from production and marketing viewpoints.