What is an Echo?

Have you ever gone to mountain or a valley? If you get there try to shout "Hello" then within seconds there will be a voice that respond. Whatever you shout that voice will say the same thing. That's not a ghost voice but our voice is returning. This is what we call an echo.

The word Echo comes from the Greek. In ancient times in Greece echo is described as the voice of a girl named Echo who fell in love with a man, but unfortunately he did not love her. Eventually the girl disappeared, she faded away and nothing was left but her voice.

How the sound returns

Echo comes from our own voice back due to the reflection. When we shout, our vocals cords vibrate and produce sound waves and the waves will travel through the air. If the sound waves hit a solid materials such as walls or mountains, the waves will bounce and head back. In short time the returning sound waves reach your ears so you can hear it.

Why we cannot hear the echo in our house

There are several requirements to make an echo. First there must be a high sound like when we shout, then number two there must be a solid molecules for the wave to bounce back. A sound has a very high speed. It could reach about 1100 feet in 1 second. We will not be able to hear echo if the distance where the sound waves bounce is too close because a sound needs time to travel. If you say "Hello" to a wall close to you, the sound does bounce from the wall but it goes to you in so little time that you cannot make it out. For your experiment you could go to a mountain, bring your stopwatch and start to count how long it will take for your sound to return.