I used to set off car alarms with my carbon Gia.Ca.Moto slipons, and they weren't as loud as the Termignoni cans. If I ever found a parked car that "honked" at me as I rode by, I would try to go back and set it off half a dozen times. If I saw the owner, they got a rude gesture before I wheelied out of there. ;D
I got tired of how loud my pipes were, so I sold them and switched to stock pipes with three inches removed and slight rerouting of the internals. They let the proper Ducati sound out, but are about half way between the stock pipes and the typical slipons in loudness.
I was recently reading an old Motorcyclist magazine article written by one of the Erion brothers from Two Brothers Racing talking about optimal pipe design. He felt Carbon Fiber was a poor choice of material to build pipes from. The only advantage was that you can touch one when it is hot and you won't get burned (I've verified this). He thought titanium was a much better material. Carbon fades or changes due to both heat and too much sunlight, so it's higher maintenance than other materials.
It was interesting that he felt fiberglass packing was the only thing to properly absorb the excess sound. You have to be concerned about blowing it out after a while, but it also can absorb things from the exhaust and get brittle so that it doesn't absorb sound as well. I repacked my pipes before I sold them to make sure they would absorb the sound properly for a few more years.
It's hard to tell the difference in sound with most pipes. I know that Termingnoni and at least one set of Two Brothers pipes I've listened to are a bit louder than average. The cored and shortened stock cans are also loud, but I don't consider the sound the produce to be "good". You need something inside there to absorb some of the noise before letting the sound out.
I would like to see more pipes that are designed to sound good without being so loud. I guess I must be getting old or something. 8)