If you’ve ever been inside a large canyon, you’ve probably observed the wonder of echoes firsthand-but how do they work? The echo occurs when a sound repeats itself, fading from loud to soft in seconds. The echo occurs because some of the sound waves in your shout reflect off of a surface (either the water at the bottom of the well or the canyon wall on the far side) and travel back to your ears. For a place to be able to produce echoes, it must have certain features. For one, the size of the obstacle/reflector must be large compared to the wavelength of the incident sound (for reflection of sound to take place). For another, the distance between the source of sound and the reflector should be at least 66 feet (so that the echo is heard distinctly after the original sound is over). Lastly, the intensity or loudness of the sound has to be sufficient for the reflected sound reaching the ear to be audible. The original sound should be of short duration.
The farther away the surface is, the longer it will take for the echo to come back to you. One could theoretically tell how far away an object is and how fast it is moving by an echo.For example, bats can tell the location and movement of moths using echolocation. The bat sends a sharp click or chirping sound, then hears and processes any echoes off other objects in the area. Bats have large ears that are very sensitive to sounds in certain wavelengths. Their brains also help by processing the distance from and the size of the object as well as how fast it is moving and where to. Using this echolocation, the bat finds moths easily in the pitch dark.
The dolphin is another mammal who uses echolocation. With what are called “phonic lips,” a dolphin makes clicking sounds. Almost all other mammals produce sounds by using their vocal cords–but not the dolphin. It instead uses its phonic lips to emit clicking sounds. The lips evolved from what was once the dolphin’s nose. The dolphin forces pressurized air through its phonic lips, and the air vibrates and comes out sounding like clicking. When the clicks bounce off of the object the dolphin is interested in (that is, when the echo occurs) the dolphin then gets a mental picture of that object.