New - WLA-218BX Dual 18" Subwoofer, iSGA ready!
There's no going back !

Low frequencies usually go everywhere.....
A lot of output energy can end up in places where the audience do not benefit from it.   Having great low frequencies behind the stage is a waste of power and energy.
It’s for this reason the new WLA-218BX can be easily deployed in an Inverted Stack Gradient Array (iSGA) configuration.
WLA-218BX uses the acclaimed Reason-X 18” subwoofer drivers.  With 4.0” voice coils and an impedance boost around 35 Hz, these efficient drivers simply deliver extreme bass.  

And, when used in the iSGA configuration, they deliver that bass directly into the face of the audience.

Read more here