At the end of the book, Paul's voice is so powerful that when he tells Helen Gauis Mohaim "Silence!", Herbert says something like "the word seemed to take substance as it travelled through the air between them" - so the voice weapon in Lynch's movie was correct, except that a) Paul didn't need to wear something on his neck to do it and b) only Paul could do it. It was a confirmation of the Fremen Legend: "And his word shall bring death eternal to those who stand against the Righteous"