Same situation. When I get excited, I guess I can speak loudly, I think it's a natural result of my excitedness, and thus appropriate, but people frequently tell me I'm being too loud.
Also, when I disagree with someone, there are times then others will say I'm yelling at them, and I don't see it because I don't feel angry enough to be yelling (believe me, there are times when I know I am!), but if they feel that way, they can't be wrong.
The exact opposite occurs when I'm on the phone, in that situation, nobody can hear me, and always ask me to speak up...
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O Wonder! How many goodly creatures there are here! How beauteous mankind is!