[Jim Hodgson]

http://www.youtube.com/watch?v=MHeyPJS00Fc

I've e-mailed the guy who posted the video, but he hasn't responded.  These OBs are pretty attractive, I think, and I'd like to build a pair.  So, plans would be very helpful if they're available.  Sorry -- don't know enough about this to know if these are pretty common, one-offs, or somewhere in between.  (Just dipping my toe in the water with this, actually.)  Thanks for the help!

[zmyrna]

The speaker in that video looks like a naked (crossoverless) 8" Fostex driver (probably FE208 Sigma, out of production now) on a piece of plywood. The video just aims to demonstrate the open baffle sound vs a box speaker. It is not an ideal design because: A. Fostex driver has low Qts, B. it is a rather small baffle for that driver.
If you want to try sth similar, you may consider a Supravox 215 Signature Bicone on a JE Labs Open Baffle or this:
http://www.audiocircle.com/index.php?topic=70807.0

For lower budget, look into vintage drivers.

[planet10]

The OBs have FE208Sigma the old 208.

The poster of the youtube has, IIRC, a thread on diyAudio about these.

dave