Being in radio, I’ve gotten used to the sound of my voice when heard outside of my cranium. But it is strange at first to discover what your voice really and truly sounds like. It’s different, isn’t it, then how you think you sound, or what you think you sound like. Why do you sound one way when you’re just talking and differently if that speech is recorded and played back?
Most often, the sound you hear when you talk is a combination of two different sound signatures – the one coming out of your mouth AND the one that bounces through your head (coming from the throat upwards). This dynamic of sound structures is heard only by you and not the outside world, which is why you sound one way to yourself and differently to the rest of the world.
The flesh and bone inside your skull and even your neck help to create lower-end frequencies that you hear, which can give the impression that your voice is deeper than it actually is. This dynamic is put into perspective very well here:
Imagine what James Earl Jones must think his voice sounds like compared to what we hear.