DIY 60 hz hyperbolic bass horn

Here's an upcoming project that's bound to generate amazing sound and, perhaps, social interest:

This crescent shaped, hyperbolic horn employs the 10" B&C 10MD26 mid bass driver. You can locate this device on Parts Express for the reasonable price of $160.00. The only downside to this driver is the Xmax, which is limited to 1.5mm. Still, this horn would work remarkably well with a 3 watt triode, as 2 watts is all that's required to generate 115db which doesn't tax the amp, or clip the speaker. 

There's another 10" B&C driver, the 10PLB76 at $188.00, that performs almost as well, but drops off at 400hz vs. the 10MD26's 500hz roll off. The 10PLB76 has the decided advantage of a 6mm Xmax. That's a substantial increase in cone travel.

Below: B&C 10MD26 at 1 watt input:

Same driver handling 2 watts at max SPL:

Below, the B&C 10PLB76 does a remarkable job with 25 watts. You'll definitely want to cross your mid-range horn at 300hz.

Hornresp suggests that I'll have a fairly easy time operating the horn between 60 and 500hz. Because the horn is crescent shaped, there'll probably be some minor loss of information in the upper frequencies. Only time will tell. Because the crescent is gradual, the upper end roll off shouldn't be excessive.

I felt rather please when I discovered that the B&C 10MD26 delivers a decent, and extremely fast, impulse response. This should lend itself to jazz, classical, or chamber music.

So how's the modeled efficiency and distortion at the 60hz cutoff?