Finally, here is some very useful information Karen Ross posted to the phoenix some time back:
Several months ago I wrote a few voice tips. I'm not sure where I posted them, so you may not have seen them. I'll repeat them here in case they might help.
Resonance - involves more than the voice box. Did you ever make soda straw horns? You pinch one end and clip the corners. Then you stick the clipped end in your mouth and blow. The clipped end vibrates and the horn honks. If you cut the straw shorter the pitch rises. If you use a smaller diameter straw, the pitch rises. So both the length of the resonating structure and its width control the natural resonance frequency of a chamber.
If you look in a mirror and shine a light into your mouth when it's open wide, you'll see two ridges of flesh on either side of your throat. Do an experiment. Use your muscles to close the ridges of skin closer together then relax and let then move back further apart. Now do the same excersize but make a constant tone with your voice. You'll notice that the pitch rises and falls as you first pinch the throat part-way closed and then allow it to relax and open. This is easy to see because you can do it with your mouth open.
For the next experiment I don't think you can really see what's happening but you can feel it. Open your mouth just a little (about the thickness of a finger) and make a tone. Pull your tongue back towards the back of your throat. The character of the note changes. Relax it and notice how the pitch falls when the tongue moves forward again.
By contracting your throat and controlling the position of your tongue you can alter the size and shape of the resonating chamber that determines the basic sound of your voice. The tension on your vocal chords determines how high they can vibrate but the size and shape of your vocal tract determines the final character of the sound. I suspect that there is also a component that determines how much of your throat and lungs also get to participate. If everything is relaxed, the voice can resonate down in your chest. That isn't good. The larger diameter windpipe and larger air capacity allow lower frequencies to layer on top of the voice. Pinching off those seems to be important but I'm not sure how I do that. All I can say is that when it feels like I'm talking through the mask of my face, the vibrations from deep in my chest are removed as a dimension of the sound. When they are allowed to be included, the sound is very male...not good.