I have a weird, double-edged history with this. When I was a child, teenager and up into about my mid-twenties, I was deeply uncomfortable speaking to most anyone who was not my own family or family friends, and I went through years of alternating between selective mutism (around strangers and at school) and speaking fairly quietly.
When I was in my mid-20s I had long had an interest in psychology, believing I was a broken, odd person who just needed to find out how people are "supposed to behave" and then I could fix myself. I was born in the 1960s so diagnosis for Asperger's didn't even exist for me at the time -- I just knew I was a broken item that didn't seem to work the way other people work.
So part of "fixing myself" was to force myself to be more social, more verbal, less "shy" and less introverted. I pushed myself, but it's like I swung my pendulum too far the opposite way, because after passing through a quite well modulated phase, which were my best years, I think, I gradually became too loud when I spoke, and I began to realize I didn't seem to know how to modulate myself.
I still wrestle with this now, in fact in recent years if anything I think I've become louder, but I have a theory on why I'm doing that.
Lately in my life I feel I'm not heard, both literally and figuratively. I have this deep feeling that of all the people currently in my life now, nobody actually listens to me when I speak.
There is a culture of talking-over, cross talking, interrupting, where I live now, and I constantly feel like whatever I say truly is not being heard or cared about or listened to or given its turn to be part of the conversation. I think this is why I now tend to practically shout when I talk to someone. Deep down I don't feel like the person hears me even in the figurative sense of the word. Somehow in my instincts that translates to me thinking I need to talk louder (don't ask me why).
It also doesn't help that lately ALL my conversations take place outdoors, often with the roar of fast-moving traffic as a background!
I can't even hear myself think, let alone hear myself talk, and so I shout.
I long for the time when I got the volume just about right, and was hanging out with friends in quieter places such as my home or their home, and I actually had quite a relaxed volume then.
And I think I was able to maintain a normal volume during that time when I had people in my life I felt respected what I had to say, cared about me and seemed to actually listen to me and not interrupt me. I'm constantly interrupted these days and I don't feel surrounded by anyone who listens, now.