Echoes occur when sound waves bounce off a surface and return to the listener, requiring specific conditions such as a large reflective surface and sufficient distance. Bats and dolphins utilize echolocation to navigate and hunt by emitting sounds and interpreting the returning echoes to determine object location and movement. Key factors for producing echoes include sound intensity, short duration of the original sound, and adequate distance between the sound source and the reflective surface.

1. The Basic Physics 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? 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. 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). Another requirement is that the distance
The farther away the surface is, the longer it will take for the echo to come
back to you. 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 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 fast it is moving and where to. With the
bat’s talents and attributes, echolocation is simple, leading the bat directly
to its meal.
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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). 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.
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2. 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. By sending pressurized air past these lip-like structures,
the air vibrates and click sounds are produced. 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.
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