I can't pinpoint the page on which I've seen it, but I've sacrificed my DT 1350 pair for DIY experimentations, as I believe it's got the best driver currently in production for portable headphones. And I can confirm that it has a 30mm or so driver.
Although the size may be small, it has a very, very good bass extension and control - impressive to say the least. Also, if one removes all the damping inside the DT 1350 cup, as well as the side rubber parts and free all the holes on the back of the driver, the DT 1350 becomes extremely dynamic - which shows that really, the driver is something, and that the main reason behind the DT 1350 "flatness" isn't the driver but the damping design.
I've actually listened to the DT 1350 in "open mode" : I put the pads on the two driver plates and brought them to my ears. The result was surprisingly good - as if the drivers were designed to be put in an open headphones.
I see a few reasons why Beyer went for the default damping design inside the DT 1350 - but I really feel it could have been made better with a better cup design. I'm not sure I can improve on what's already in the DT 1350 (after all, I'm no acoustic engineer), but I'm sure a more careful / clever cup design would have improved the sound.
Hey Maya, I'd like to see some pictures as well, Ive seen the insides but never took the driver out of the capsule or removed any damping.