Question

How does singing from the diaphragm, instead of the throat, help improve the voice quality of a singer

Answer 1

You can't sing from the diaphragm. No one can. What the diaphragm does is to help you breathe in. It doesn't help at all with singing. You can't sing from the diaphragm because you vocal cords are in your throat not in your diaphragm. Your diaphragm works all the time helping you to breathe in it even does this when you are asleep at night.