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An Overview of Echoes

Have you ever wondered why, while in a large canyon or cave, your voice seems to bounce off the walls and come back to you? 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. Of course, an echo can’t be

produced just anywhere–the place must have certain characteristics for it to be possible. 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). Secondly, the distance between the source of sound and the reflector should be at least 17 meters–about 66

feet (so that the echo is heard distinctly after the original sound is over). The last requirement is that the intensity or loudness of the sound must be sufficient for the reflected sound reaching the ear to be audible. The original sound should be of short duration. The length of time between the moments you shout and the moment that you hear the echo is determined by the distance between you and the surface that creates the echo. Not only do echoes tell how far away an object is, it can also show you how fast the object is moving and even its shape. This is called echolocation and bats use echoes to find moths while flying around at night. A bat can emit a sharp clicking or chirping sound, then sense the echo bouncing off of any other object in the area, thus determining its location. 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

 

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fast it is moving and where to. Using this echolocation, the bat finds moths easily in the pitch dark. Another animal that relies on echolocation is the dolphin. A dolphin produces these click sounds using 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. By sending pressurized air past these lip-like structures, the air vibrates and click sounds are produced. This process of echolocation gives the dolphin a mental picture of what object it is investigating.