Most Star Wars fans know that the guy in the sith lord suit didn’t do the voice of the guy in the suit. David Prowse, an English actor and body builder, was the body in the Vader suit–but he wasn’t the face in Return of the Jedi. (That poor guy, couldn’t catch a break.) His voice is… the opposite of James Earl Jones. While Prowse did try to sound commanding, he can’t compare to the booming, commanding bass that we associate with Vader.
Compare them for yourself. It’s weiiiird.