I'm hardly ever loud when I'm speaking. Mostly after a "conversation" I come away with the strong impression that the other person was too "full of themselves" and not sensitive to my ideas, until I think back and then I begin to wonder whether the reason they talked over me so much was because my words were so quiet that they didn't realise I was speaking. On the other hand, I'm sure that a lot of sales people, teachers and officials deliberately try to capture the agenda and are engaged in a highly competitive game, and they're delighted when a mild-mannered individual turns up, ripe for manipulation. But a quiet voice should not mean that it's appropriate for the other person to take the lead and call the shots. Silence is NOT consent.
I tend to go limp in meetings, and probably frustrate everybody by seeming to go along with whatever they're trying to push through, only to later reveal that I have no intentions of co-operating with their agenda. But if they wonder why I didn't speak up at "the right time," my answer is simple - "because you bastards wouldn't let me get a word in edgeways!" I might word it more politely than that, but it does make me angry.
I've got this ideal that everybody should talk quietly and be particularly attentive to those who may have opinions but are too timid to voice them, so I wait to be asked.......unfortunately out in the real world conversation is mostly a game of push and shove, and you have to talk over the competition or they'll talk over you. But even though I've known that for ages, I still don't seem quite able to shout up. I can only do that when I get angry, as if I feel that quiet, sensitive talking is an important courtesy that should only be discarded when dealing with brash, insensitive morons.
There have been a few times when I've talked loudly because I'm feeling enthusiastic about what I'm saying and haven't noticed my volume is too high, but I quickly realise what's happened, get embarrassed, and tone it down again.