I think saying that it requires a lot of energy. To say that there must be a sound. Sound: sound energy. This is the energy in the sound energy, but communications requires an intermediary. An intermediary, that is the air. But the sound energy is it that is caused by an action from us. Examples of sound energy as the energy from the talk. Energy from the music from tapping ,hitting , sound of animals and etc. I my thinking the sound energy is energy that is very important is missing.