What is the biggest difference in these two models? Is it primarily bass extension?
Has anyone compares the two ?
I presume you are talking about the Veracity HT2-TL's vs. the Supercharged SongTowers. Actually, there is another model to consider as well - the Veracity ST's.
The difference between these models is the size of the woofers.
The Supercharged SongTowers use 5" Seas Excel woofers. The Veracity ST's use 6" Seas Excel drivers which feature 6" cones in a 5" frame (great engineering). The Veracity HT2-TL's use 7" woofers.
All of them are tuned to the same F3 of 34Hz.
The larger the cone, the more air it can move. So while then don't play deeper, the Veracity HT2-TL's will move more air down low giving the impression that they have more bass extension. They don't. But they do sound like a larger speaker.
You would assume that the Veracity ST's fall about half way between the Supercharged SongTowers and the Veracity HT2-TL's. But actually, the ST's are closer to the HT2-TL's in terms of bass output. So the Veracity ST's provide almost the same bass response as the HT2-TL's in a cabinet size similar to the Supercharged SongTowers.
I hope this helps.