Looks like he used those for the bass under a certain frequency as he still had corner loaded 18" horns.
This is primarily why I don't want to deal with modern subs
I honestly think that has a lot to do with the more modern subwoofer drivers typically used in modern subs having stiffer suspensions and heavier cones to withstand the higher power thrown at them which causes the drivers to not respond as quickly as the older subs would.
I figure perhaps using some super scoopers as the subs and if they go low enough then that will be all I need.
Given the space I need to fill I'd need the longer throw ability of the horns.
As it stands now with the Yorkville subs the bass is much louder by the subs and decreases in output as you move away from them.
That said I've heard the 4520 cabinets at another rink of similar size (maybe slightly smaller) and the bass seemed to not decrease as much moving away from the subs, and even though the low bass under 40Hz was not really there what was there sounded so natural and present.