I am a female in the military who sometimes needs to speak in a command voice. My voice is high pitched. I want to figure out how to be loud enough without sounding annoying.
The single most important thing is to NOT strain the voice. High pitches and nasal resonance can be more acoustically efficient; they help the sound travel well and help you to be heard. To make the sound fuller and more complete, the voice needs to be supported from the lower ribs and to be completely unconstrained by the tongue or throat muscles. The larynx should also stay in its low position rather than raising.
So here’s what you do:
Place your hands on your lower ribs and feel them expand as you inhale. If you can’t feel this, try grunting. You don’t want to lock the throat in this way but it will help you feel the ribs engage.
Now speak loudly and try to feel that your ribs continue to expand or at least to stay open for the duration.
Also, make sure your tongue isn’t pulling back into the throat.
Once you have the ribs working and the tongue released, touch your larynx very lightly. You can tell where it is by the little bump we call the Adams Apple. Make sure it stays in place rather than raising when you speak loudly. If it doesn’t at first stay in place, just keep trying until you figure it out. It’s a little like shooting baskets — eventually you get the coordination together and the ball goes through the hoop.