I see the original posting is a little old and the original author hasn't responded since his first post date, but I can try to give a little insight since it seems to have picked up a little steam again. I am no exhaust engineer or guru, so this is my layman's guide....
Glass packs are essentially a straight through design with only a little sound deadening material. They are designed for the best possible flow while helping to quiet the engine. So, straight pipes and glass packs are essentially the same sound, including raspiness.
Turbo mufflers also contain a packing material similar to glass packs, but are not a straight through design. The changes in direction essentially bounce the sound waves around within the muffler and through the packing material to help control the sound it emits.
Both turbos and glass packs have perforated or louvered tubes within the muffler for the sound to travel through to quiet it. Turbos are inherently quieter due to the extra surface area of the louvered and packed tubing as well as the changes of direction within the muffler.
Chambered mufflers are designed to give a certain frequency of sound and cancel other frequencies. They are divided into "chambers" which have different diffusers in different design layouts in order to cancel frequencies and have no packing material, giving them pretty good flow. Chambered mufflers, IMO, are the only mufflers engineered to give a wanted sound while canceling unwanted sounds such as raspiness.
For comparison, here are a couple vids of my Cobra II, one with turbos and one with Thrush 2 chamber mufflers. The 2 chambers sound a lot better IMO. I have to give a small disclaimer here though, when I installed the 2 chambers, I also installed an H-pipe.....
Turbo:
View: https://youtu.be/K5KE6B-hIqU
Chambered:
View: https://youtu.be/oIreFUOfLZw
Another chambered:
View: https://youtu.be/lgGduu0N3Rw
I hope this helps. Like I said, I'm no expert on exhaust systems by any stretch of the imagination.....