I just finished building a pair of Ripole subs for a friend who liked mine. I think they turned out rather nice.
Ripoles are not well known because no company that I know of sells them.
A Ripole is a slot-loaded, folded-baffle dipole with opposing drivers in a push-push configuration. They have a cardioid radiation pattern which blends quite well with ESL's. Their off-axis null is less prone than other sub types to excite the room's resonance modes.
The outer woofer cases are 3/4 AA red oak plywood with quarter-round oak moldings along the box edges.
The center C-section is 7/8 thick white oak planks, stained a contrasting color, and aligned to the outer cases with dowels. The three-section assembly is bolted together with (4) 1/4-24 all thread rods and button-head cap nuts.
Each sub uses a pair of 12" Peerless SLS woofers, wired in parallel and same phase. As you can see; they are made so compact that the woofer magnets protrude thru the sides of the cases.
They are a lot of work to build but they are pretty unique and I really like their compact size and unobtrusive sound.
The bass notes just seem to rise up from nowhere and recede back to nowhere-- completely un-localizable.
I have CAD drawings if anyone is interested.
