How can I achieve the voice I want?

I’m talking about being able to speak from the diaphragm, with deep guttural resonance. I’ve read plenty about it, and I’ve been doing some exercises, but nothing has helped all that much. I sound good when I wake up in the morning, but after an hour or so I get the “throat voice” that makes me hard to hear when it’s loud and, perhaps, a little bit ineffectual-sounding. Any advice on what to do or read? If you seem helpful, I’ll probably want to PM you.