@phusis , I need to build one of the horns, maybe something along these lines and try to get lower extension
https://www.pioneerproaudio.com/en/products/xy-series/xy-218hs
On a different note, the tekton definitely gets under 20 (not some exaggerated spec). As I mentioned, it’s a solution "on the cheap" with some phenomenal bass for his speaker design.
Horn-loaded subs are altogether different beasts and bigger still. From my chair there are no better "audiophile" subs than horn-loaded variants when it comes to smooth, layered, effortless and enveloping bass reproduction. They’re both less conspicuous in the mix and more shaking-the-air crazy powerful when called for, whereas direct radiation subs make themselves more known overall. The latter can be a quality to some ears with its more "thumping" and animating character, whereas horn subs have a more fluid omnipresence of bass.