Thanks styjp for starting this JBL thread.
I know a lot of the discussion has been around sealed boxes for near-field use, but to me the major benefit of the Infinity driver was the ability to obtain flat response down to 20 hz and below in a reasonably sized ported box.
As noted before, the CS1214 wants a larger ported box (7-8 cuft) for optimal low end response. I was going to recommend the JBL GT5-12 however after simulating it against the CS1214 in a non-optimal smaller ported box there isn't enough difference to warrant passing up the current crazy deal on the CS1214.
Here is the maximum output for each driver in a 4.5 cuft net enclosure ported to 20 Hz and for the CS1214 in a 2.5 cuft sealed box.
For a real world example here are the details of my Infinity setup. (I think I posted a similar graph over on the Infinity thread a few weeks ago.) Similar results can be had with the CS1214, but likely a couple db less output below 30 Hz.
I have four subs, one in each corner of my small theater (13'X14'). A 1262W in each 4.5 cuft net cabinet ported to 20 Hz driven by an NU3000DSP, high passed at 20 Hz, Butterworth 24db/octave. Measured from the listening position at back wall center. One could argue that the distortion just above tuning is excessive at this level, but I wanted to take the system to the limit. I can improve the response below 20 Hz by switching to a 12db slope however the distortion skyrockets below tuning. My understanding is that 115 db from 20 Hz and up is considered reference level, which my setup makes (just barely).
For those considering using multiple 12's in sealed boxes realize that your response will be about 10db down at 20 hz, which would require a dozen of the CS1214's and 3000 watts of power to reach reference, even in a small closed room.