That pic of a single cabinet looks a LOT like the "Big Bertha" 18 inch folded horns i built and ran under my PA many years back, except they're missing the ports in the woofer chamber.

We built 8 of em, loaded with 2240's and driven by a pair of FET-500's. Outdoors, you could easily hear the kick drum and bass guitar parts 2 or 3 miles away in front of them.

They come up in conversation from time to time, and those familiar with them still affectionately refer to them as "the cop callers".