Many people have experienced the phenomenon of an echo, often while in a large canyon or cave. An echo is a phenomenon we experience often. When you shout into a well or a canyon, the echo returns to you a moment later. 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. There are certain basic requirements a place must meet in order for it to produce an echo. Firstly, the size of the obstacle/reflector must be large compared to the wavelength of the incident sound (for reflection of sound to take place). Another requirement is that the distance between the source of sound and the reflector should be at least 17 meters, or 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.
How long between the time you make a noise and the time the echo occurs depends on how far away you are to the surface. Echoes demonstrate how far away surfaces and objects are, and they can also determine if objects are moving as well as how fast. This is called echolocation, and bats use it to find moths 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 are also able to process the sound of the echo coming off a flying moth to determine how far away it is, its size, and which direction and how fast it is flying. With the bat’s talents and attributes, echolocation is simple, leading the bat directly to its meal.
The dolphin is another mammal who uses echolocation. With what are called “phonic lips,” a dolphin makes clicking sounds. The dolphin, unlike us, does not use vocal cords to emit sound. It instead uses its phonic lips to emit clicking sounds. The lips evolved from what was once the dolphin’s nose. The dolphin sends clicking sounds through the phonic lips as pressurized air, which then vibrates to produce sound. 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.