Zlow, I read those links...LOL!...wow! talk about confusing. Yeah, that's what I was thinking about when I said "not an exact science". I wonder where they get their term "chambered"? That looks about as straight-through as you can get...at least as far as the muffler is concerned.
Still, I guess when we're talking about Flowmaster, their take on the chambered muffler definitely seems to be the diversion plate and separate chamber approach. I found this on their site where they get more into the differences on the straight-through vs. chambered...at least as far as their terminology is concerned.
Seems like when you're talking about some of these brands, however, you're just going to have to look at their muffler and see if it fits your definition...LOL! I guess for generalization, I'm going with "chambered" to mean that there are actual diversions in the muffler body that truly divert the exhaust stream into pockets or chambers, and you can't see through it. If I can see through a muffler from the opening to the outlet to any degree, I'm going with straight-through. I guess it depends on who's dictionary we're using...LOL! Very interesting.