The density vs syllabic speed concept is pretty widely known, but I'd be interested in analyses of accents inside languages. Why are some accents much slower th

The density vs syllabic speed concept is pretty widely known, but I'd be interested in analyses of accents inside languages. Why are some accents much slower than others, and how is that not a serious disadvantage? I have firsthand knowledge of the fact that when I, as an American Southerner, try to speak as quickly as a Northerner my mouth falls to pieces.