4 -year-old speaks to me and my family members too loudly.When he is travelling with me also he speaks loudly he never minds about others.But in school or when any unknown people to him asks some questions he fells shy or answers in very lower volume.Whether he will decrease his sound naturally while talking to me or we must explain him.
Yes, he will learn to moderate his tone over time. He feels safe with you, and so expresses his excitement (which at four is basically everything!) by being louder, while he has some anxiety that makes him be quieter with others (as most kids do that age). As he gets older both of those things will reduce while he also becomes more aware of the social reasons for moderating his tone!
My kids still are too loud sometimes (7 and 9) but are much more moderate now; around six or so is when that kicked in.