15” horn 3 way with cardioid like woofer

I am designing a new speaker using the audio horn x shaped horn with a hf1440, a sealed 15” midrange, and a cardioid like woofer playing from around 200hz down, one for each channel.

I am considering a damped u frame, either a single 18” or a slot loaded U frame with 2 12”s.

a damped u frame has a cardioid like response, and I am trying to create a subwoofer that won’t cause the bass to travel excessively through my condo. I could also make an active cardioid sub, a ripole, or many other designs. A regular dipole or h frame would probably be less optimal as the subs would have to be placed within 3 feet or so of a wall.

Anyone have any idea which. Woofer/sub. design would be my best bet for high sound quality, while leaking from my listening space as little as possible and cancelling unwanted bass energy?
 
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