American voices

[JayCee]

Since many of the posters here seem to come from the US, I want to ask you something that has been puzzling me for a while.
Why is it that americans talk so loud?
Is it something they teach you at school?
where does that come from?
I use public transportation rather frequently and especially in the summer months often have american tourists travelling with me.
The other day there was this dude bragging on about his air condition and how he paid it and used some credit, blablabla.
I had to insert my emergency ear plugs and for the rest of the journey I still heard the words "air condition" "bank account" blablabla his voice was so piercing (that is the other thing, if at least their conversations were interesting ! then it would not be so annoying having to listen in. Haha.)
They seem absolutely oblivious that there are other people around them who maybe want to read or sleep on trains.
Over here there is some tacit consent which most people observe, that is when you are in a public place and have a conversation with someone you don't raise your voice as not to disturb others around you.
Americans don't seem to have that.
So I wonder why.