The ZR subs are maybe from many years of trial and error learning. The subs are a massive monsters that have it’s muscles in the right place to be able to perform to maximum. As an example we focused on the massive motor structure and voice coils but kept a simple good sounding enforced paper cone that will give you the best performance for your money HIGH SPL Subwoofer - One woofer to rule them all...
This is the most competitive high SPL woofer on the market... NO BULL... 
2,5” Voice coil 8mm2 cables from voice coil
Stitched surround
High roll surround for massive Mechanical - XMAX
Super-strong 100oz magnet - Hi-Grade Quality double stacked