It is sometimes rare to get a classroom that behaves perfectly. There are always those few students that are having side conversations while the professor is speaking. These are some of the things you can do to make sure you are managing your classroom well.
Sometimes the hard line approach actually can work. By letting students know you will not put up with their disruptive behaviour, this makes the classroom a better learning environment for all students.
Some ways of dealing with the noise levels are the stop speaking until the room has quieted down. This tends to be an effective method that works, without the professor needing to shout.
Another method that tends to work is let the students know that if they are going to make noise in the class…you would prefer they do not show up. If they are going to be disruptive, perhaps they should not show up to class at all if they would rather chat about such things as Facebook.
Another method to ensure that your classroom is orderly is to make sure that you have a participation or a professional conduct mark as part of your class. Make sure to keep track of those students who seem to constantly be the noise makers and make sure you penalize them at the end of the class for being so disruptive. Make sure at the same time that reward those students to actually come to class to learn.