I'm from the U.K and have 8x of the Zxi 12" sub woofers in a walled system. Powering the subs with a 15k rms amp @ 1ohm @ 14.4v.
Purchased at a bargain price too.
These are really nice, smooth sounding Subwoofers.
Very pleased with how they sound and they get pretty loud too.
Best scores these have done in the (((pd))) propper droppers SPL format.
158.85dB @40hz
158.03dB @33hz
156.84dB @25hz
153.85dB @20hz
At every test they have been getting louder, hoping for a 159dB @ 40hz and a 154dB @ 20hz once the subs have been properly run in.
These subs do have limits. They are after all not designed for mega power handling and are not the type of subs that you can throw shed loads of power into.
So don't expect them to last if you are constantly giving them well over their RMS rating for long periods of time.
But used within their limits, they are proving to be a very nice sub. Certainly doing well in my set up.