The difference is really n the lower octave. Having said that I will add that even the rigid metal frame is not enough to totally contain the energy of the speaker when playing lower bass information. As albert will most likely verify you can improve things still further by adding some ballast weight to the transformer boxes. I have about 80 lbs of lead shot resting on mine and have filled the frame tubes with sand. This has added a noticable increase in delicacy and defintion to the very low end as well as marginally improving the imaging overall.
