Why do we cup our hands around our mouth to call someone far away?

When you speak or shout or sing or even whisper, the vibrations of your voice send sound waves through the air. These sound waves travel from your mouth in all directions out straight, to the right to the left and to all the places in between. But when you cup your hands around your mouth, you are pointing the sound waves in only one direction and keeping them from spreading out in all others. By doing this, you are giving your sound waves more energy and making them louder and stronger.