(subs brought out for pic - normally in the corners w/gills)
If actions are proof of insanity, then I'm nuts or, at least,
I use two subwoofers each with an 18" McCauley ultra sub.
I was going to build them out of 3/4" MDF with a white oak veneer,
but I found a set of 3/4" MDF walnut veneered three way cabinets for $25.
Here is the transformation from three way to single sub:
My 6174 Drivers
Recut for 18" McCauleys
Redo the input connector
Recut and make new bottoms
Create ports in the horn cutout
Brace and foam
Install the McCauleys