> He’s never mumbled a line in his life and you can understand everything he says during quiet dialog. You can be true to life, quiet AND understandable.

Its almost all about projection. You can come across as a "quiet" speaker and still manage to be heard when you're projecting and enunciating properly. Projecting isn't about being loud, its about being heard.

I have a tendency to mumble a lot when I'm not thinking about it. Thinking about projecting my voice brings things across better, and its not really all about being louder.