- from Sound and Vibration
Everybody has heard an echo.
Maybe you’ve been in a tunnel or a cave and shouted, “HELLO, OUT THERE!” and heard your voice faintly repeated back to you—maybe even multiple times: HELLO, HELLO, HELLO…What causes a sound to echo? Just like a mirror reflects light, an echo is a reflection of sound. When a sound wave rolls through the air and hits a flat surface (such as a wall), some of the energy from the sound wave will be absorbed or transmitted and some of the energy will be reflected so that it bounces back through the air. Under certain conditions, the sound reflection is so good that you can hear an echo.