Passion, personality and vocal physique = magic
Sometimes other people have already said what one wants to say. I came across this great site with lots of helpful tips about how to have greater speaking power. I wanted to say it (stomp foot) so the next best thing is to share it and recommend you read it.
The particular point to get is that it is the combination of passion, (intention, aligned with personality and content) and vocal agility that creates the magic. One without the other is like fish without the chips without the Watties sauce.
And remember….. generosity of spirit is at the heart of every great speaker.