Found this on the internet
) The tweeter and woofers are both Definitive in the BP30 - the BP20 used a Vifa soft dome tweeter and a Vifa midbass which is now made by Scanspeak... I would say both of the Definitive drivers are a step up in alot of regards....
2) The port on the BP20 is just a regular port
3) The port on the BP30 is a quasi transmission line where they recess it in the cabinet with an oval cutout about 3 times the size of the port exit diameter, thus causing it to load like a transmission line thus increasing bass by about 3-4db in the low end... and allowing it to dig a few octaves deeper.
4) The cabinet on the BP30 is built far superior and there is a solid board that spans the inside of the cabinet separating the inside and outside woofers from each other where this is not the case in the BP20
The BP30 is a rightful heir to the throne that was the BP20 - the original BP line was when Definitive was just getting started and you can tell they did not have near the resources as they did later on.
Also the crossovers are far superior in the "B" line the BP30 was associated with.
Hope this helps