Everything can be said calmly and with care and love, even when you're so mad and angry. Just tell yourself you will not yell and you will be surprised by the effects that will follow.
When people are angry, they are full of various emotions and those emotions drive them into aggressive behavior.
When it comes to children, yelling is nothing but a cry for help, because we don't know what to do.
Children don't consider yelling as authority, but as our weakness.
It is definitely contra productive, takes energy away and doesn't bring any results.