HEARING TIPS

Echoes – How Are They Created?

Many people have experienced the phenomenon of an echo, often while in a large canyon or cave. This phenomenon is called an echo, which has its origins in the Greek ekho, meaning “sound.” So how does an echo occur? In short, the sound waves from your voice bounce off of a surface – for example, the far wall of a canyon. The sound then comes back to you in the form of an echo. For a place to be able to produce echoes, it must have certain features. 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). 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). 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.

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. 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. Bats have large ears that are very sensitive to 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. 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. 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 forces pressurized air through its phonic lips, and the air vibrates and comes out sounding like clicking. This process of echolocation gives the dolphin a mental picture of what object it is investigating.

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