What Causes an Echo?
An echo occurs when sound bounces back from an object. When we speak or shout, sound waves travel through the air. We first hear the sound when the waves reach our ears. If the sound waves also hit a large object, such as a building or the walls of a canyon, and bounce back, we sometimes hear the sound a second time. This is an echo.
If we don’t hear an echo, it probably means that the sound waves didn’t hit the wall in just the right way. It could also mean that the reflecting surface was too small, or that the vocal sound was too weak. Besides the novelty of hearing your words repeated, echoes can be used to estimate the distance of an object, its size, shape and velocity, as well as the velocity of sound itself.
Special effects can be created with echoes reflecting off certain types of surfaces. When sound reflects off a stepped grating, the echo can have interesting effects. The most common is a “chirping” or “pinging” sound.
Ancient people used these effects: Echoes from the great Mayan pyramid at Chichen Itza, Mexico sound like the quetzal bird that is found in the Mayan area. The shape of each riser on the pyramid’s staircase measures over 10 inches, which is too steep for easy climbing but a perfect dimension to create the chirp.
Rock paintings from ancient Native Americans in Utah’s Horseshow Canyon and Arizona’s Hieroglyphic Canyon are mainly found at sites with good echoes. The placement of rocks in the areas also affects the quality of the echoes.
Some rock paintings in the French Caves of Font-de-Gaume and Lascaux have special echoes. Clap in front of a painting of horses and the echo sounds like thundering hoof-beats. But if you clap in front of a painting of a cat, almost no echo returns.
Walk by picked fence: If you walk by a picket fence that is near the sidewalk, you can hear the pinging echo of the noise you make. You can also sometimes hear this unusual effect near a flight of stairs.
Bats can find moths: Bats use echoes to find good tasting moths, while flying around at night. The bat sends a sharp click or chirping sound and then hears and processes any echoes off other objects in the area. 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, which direction and how fast it is flying, and the size of the moth. It continues to send out sound and receive echoes until it zeroes in on the moth and has a good meal.