In layman's terms as much as possible? :)
I read the relevant section of the Wikipedia article on headphones and while I understand most of it, I don't really get the practical applications in terms of the actual listening experience or sound quality or whatever.
Are they better/worse/it depends? Do they really require a better seal as mentioned on Wikipedia?
I've been looking at Audio-Technica's newest IEMs, particularly the ATH-IM70 (which I know is not BA) but I'm also trying to decide whether the ATH-IM01 or 02 would be for me. The IM02 is above the budget I set for this purchase but I might consider it if it's worth it. But really I'm trying to get a better understanding of BA in general.