Speak softly and carry a big stick.

Seriously, though, I've spoken softly most of my life. People often ask me to repeat myself. Strangely, when I speak in an English accent, I speak louder and people understand me better. Then again, my mate Jan says I was born in the wrong body, the wrong country, and the wrong era. I should have been born in England around 1945-50, and as a man.
I know for me it's a confidence thing. I was emotionally abused [sometimes even physically abused] by my own family, so my self-esteem is...erm, non-existent. Should I ever obtain a small amount of it, I wonder if I'll speak a bit louder. Or at least at a normal volume.