Echoes – Where Do They Come From?
If you’ve ever been inside a large canyon, you’ve probably observed the wonder of echoes firsthand-but how do they work? This phenomenon is called an echo, which has its origins in the Greek ekho, meaning “sound.” An echo happens when a sound wave reflects off a surface, such as the water at the bottom of a well, and the sound is repeated back to you. There are certain basic requirements a place must meet in order for it to produce an echo. One requirement is that 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). Additionally, the intensity or loudness of the sound should 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.This is called echolocation and bats use echoes to find moths while flying around at night. A bat uses echolocation by sending out a clicking or chirping sound, which echoes off any objects that are near. Luckily for bats, they have very large ears and can sense even very soft 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. It continues to send out sound and receive echoes until it zeroes in on the moth and has its meal.
The dolphin is another mammal who uses echolocation. The dolphin has a structure in its head called the phonic (or sonic) lips. Humans, like nearly all mammals, produce sounds using their vocal cords. The dolphin doesn’t have vocal cords, but instead developed its phonic lips 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.