LSA or Duration to fine tune glasspacks??

Some (old style) glasspacks/mufflers/resonators come with inward protruding louvres inside.
Installed with the louvres facing against the exhaust flow they emit a lower sound pitch, mounted the other way round they produce a higher sound. Or maybe the other way around.

In short, you can either have them sound pretty shitty, or even more and downright real shitty... ;)