It is always a fun experience to stand on a large hillside or canyon and yell a single word at the top of your voice to hear it come back to you a second later. We call this an echo, but what is really happening? Sound travels, or propagates, through air at about 340 meters per second (1115 feet per second). If you are yelling toward an object that is about 500 feet away and the surface is hard enough to reflect the sound back to you, you will hear it about a second after you initially yelled. Understanding this.