HK Odyssey
The H/K Odyssey drivers that come in the Apple Pro Speakers are right around 1.5" in diameter, and they are in a sealed enclosure. They are mighty fine, in my opinion, for multimedia drivers. The iSub (as the H/K Apple sub is called) is sold separately, or with the USB SoundSticks.
These drivers are actually smaller than those used in the Bose dual-cube speakers, but they are slightly larger than those used in their Jewel Cube speakers, and of a lot higher quality. They are aluminum-coned.
All I'm going for is percieved bass response, not actual low bass. These need to be relatively compact and look good. These are "casual listening" speakers and won't be used for much more than radio and the occasional CD, and ultimate SQ isn't absolutely necessary. The B2S look like they would be better at the lows than the Tangband 2-inchers.
Parts Express
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=297-432