[CanvasFrame]

I understand that open baffle sub-woofers sound very good due to their great transient response, and fast decay. However I don't quite understand how it is possible that they work.

If a driver is acoustically small at a certain frequency then it will radiate that frequency with an omni directivity pattern. For a 20hz signal the wavelength is approx 17 meters, much larger than the driver or any baffles used to contain the driver.

With an h-frame construction (http://www.gr-research.com/pdf/H-frame%202.pdf) the back wave needs to travel only 21 inches to reach the front face of the cabinet. That's only going to be 11 degrees of phase shift, so it would arrive 169 degrees out of phase, which would result in very strong destructive interference. Right?

[Danny Richie]

Yes, the output cancels at 90 degrees off axis. So room interaction and room boom is greatly minimized.

Output on the front side and back side is very solid.

[jlucas]

which would result in very strong destructive interference. Right?

Aren’t they wired out of phase?

As Danny mentioned they cancel on the sides but they work together fore/aft

[Captainhemo]

Yes,  an  rearward facing  drivers  are  wired  out of phase

jay