Why peoples from china talk so loudly?

In Singapore from all the Chinese it's very easy to find out who is from china. One of the way is through speaking. As mostly all the people from china speaks so loudly even to his next person. Sometimes people may misunderstand by thinking that they are quarreling and they even can't feel that people around them are not feeling comfortable specially in public transport. What is the main reason of this and how to inform them to talk gently specially in public place?