I suspect that the observation by Taleb that high status people talk more softly needs a caveat. I think people who know they have status talk more softly to convey that they don't have to fight for attention. And such signaling naturally requires the situation allow people to notice.

Which is to say in that in a more primal situation, where no one knows anyone's status, being loud and aggressive is the way to gain status when status is not yet established. And this seems like source of American loudness, America being a nation where many seek status and the hierarchy of status is often not established.