Echoes are the repetition of a sound, typically heard in big, empty spaces. Echoes may be experienced as a single repetition or as many repetitions of the original noise. Sometimes, the repetitions are so close together that they cannot be distinguished; this is called reverberation.
Sound waves are invisible waves that carry sound from its origin into the surrounding environment, whether there is anyone around to hear it or not. Sound waves travel at 343 meters per second. You can easily hear sound waves that are coming to you directly from their source.
Echoes are made when sound waves bounce off a surface and are reflected back to your ears. You hear the sound waves directly from the source, and an instant later, you hear the sound waves from that source that bounced off a reflective surface and landed on your ears, creating a "doubled" sound. Echoes are made all the time as sound waves scatter against everyday surfaces—refrigerators, fences and walls are a few examples.
Hearing an Echo
It's not possible to distinguish between the sound waves directly from the source, and the sound waves that come from a reflection, because sound moves so quickly—unless, that is, the reflective surface is at least about 75 meters away. Because the sound must travel farther to reach you from a distant reflective surface, a distant reflector gives your ear more time to distinguish between the direct waves and the reflected ones.
Certain conditions optimize the creation of audible, discernible echoes. A loud sound wave creates enough noise that you’ll be able to catch at least some of the wave’s reflection. A smooth, large reflective surface that is at least 75 meters distant offers both a high rate of directed, rather than scattered, sound wave reflection that will travel for a short period before returning to you. A quiet background will make it easier to recognize the echo when it returns to you. Finally, if you have more than one smooth surface reflecting the sound, you’ll hear it amplified much more clearly.
Some examples of where you can hear an echo are in a deep cave, where any sound echoes on the cave’s walls; facing a large mountain, where a shouted word will bounce off the mountain; and in a large chamber with smooth walls and few sound-absorbing objects. A creature that uses echoes for survival is the bat, which uses high-pitched sonar instead of visual light to navigate. Echoes can also be created artificially with sound-effect equipment. Echoes tend to convey a spooky or empty feeling when used as a sound effect.
- Photo Credit copper mountain,colorado,rocky mountains,mountain, image by Earl Robbins from Fotolia.com Sound image by Alexander Sabilin from Fotolia.com the big wall image by Josef F Stuefer from Fotolia.com bat image by Adrian Hillman from Fotolia.com
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