Since you are interested in open baffles the following link shows where you can get replacement woofers for the Carver original amazing loudspeaker if you want to built a Carver type open baffle woofer/subwoofer. Each panel in the Carver speaker had four 12 inch woofers -
http://www.dynavox.com/12inch-Carver-Am ... fer-DriverMy user manual for the Carver speakers includes the theory and analysis for his open baffle woofers (small magnet, low resonance, small moving mass, long travel). If anyone is interested I can scan that section and post it.
The only problem I had with the woofer section of the Carver speakers is that at some low frequencies (the woofer crossed over at 150 Hz) the panels would move back and forth causing doppler (IM) distortion with the ribbons. A more rigid support system for the panels would fix that problem.