Kevin, you have to do driver surface areas using the part that moves only: If we estimate effective piston diameters of 10.5" for the TV-12 and 12" for the U-13 we have (6.00 / 5.25) ^2 = 1.306, or roughly a 30% increase in effective surface area.
However, below the cabinet tuning point the output comes from the ports. Tom has not said anything yet about the porting of the Dual driver cabinets which are still in development, but he has said this in an excerpt from a post on HomeTheaterSpot concerning the porting of the new Ultra single driver cabinets:
"...we've designed all new custom tooling for the port tubing, inner flares, outer flares, and elbows to further increase port flow. Going from 3" to 3.5" doesn't sound like much...but it represents >35% more sectional area. When you factor in the new tubing, elbow, inner flare and outer flare a good estimate for the increased port flow would be around 40%. (not an insignificant amount by any measure..
Now, could it be argued that the new designs would perform a little better
Not yet, Bryan. Tom has said he expects to have pricing firmed up on the single driver cabinets within 60 days, with pre-orders hopefully starting in late April or May.
EDIT: My diminished capacity is giving Tom and his suppliers an extra month!
Actually he said he's guessing late March or April
Now there's a thought. (I have an Ultra/2, but I keep toying with the idea of swapping that out for 2 Ultras.) But then if the past is any indication of the future, SVS usually offers intro deals for new products too.