The SB3 does use the same size woofer but it is a Peerless with a larger magnet. the difference between the two is not just in bass extension. the SB3 is better accross the board. the drivers complement each other better in the SB3. More attention is paid to the crossover in the SB3 as well. I personaly use teh Von Schweikert VR-1's that claim to go to 40Hz. The NHT SB3's go to 39. There should be little difference in bass extension. NOT true. The SB3's really do go to 39 while the VR-1's start to roll off after about 70Hz. Now what the VR-1's do in the midrange and highs is a different matter all together. But if you want a reasonably priced speaker that outperforms it's retail price by a wide margin... the SB3 is hard to beat.
Good luck!
Good luck!