I usually exhausted to speak, especially if the subject does not interest me. When the change from adolescence to man I got a powerful voice, then I think I softened by shyness or unwilling to stand out, get noticed, have a very powerful voice implies not to fail or make mistakes, greater accountability and expectations of others, and other honestly I get tired and exhausted. So sometimes, after working hours or not I get the voice, I think not vocalize. On the other hand I can modulate his voice as it suits me, but in a normal state I have to make an effort to speak and raise the tone somewhat. I'd love us to be telepathic, I think my mind and my tongue are not synchronized to achieve the same speed or to express more precisely.
In conclusion: I think the tone of voice, the voice that finally we may be conditioned by psychological elements, cultural, familial, social and others.