It's a little hard to explain, sort of like a hollowness in the female vocal (maybe because of the upper mid dip?). That with the sibilants makes female vocals seem off.
It's been discussed to death in this thread, you'll probably find a better explanation by someone else.
Hmmm. Well, you know how it is. We got a novel of a HE-400 thread going on here and I'm definitely one to take shortcuts.
I've done a fair amount of searching and I haven't found a good description for why females causing more sibilance than males.
Edited by Thujone - 7/15/13 at 8:36am