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  • Smart Learning for All

  • Topic: Sound.

  • Why do we hear echoes?

  • Hey.

  • Hold On.

  • Don't go into that room.

  • You don't want to listen to me.

  • Ok.

  • Then go ahead.

  • See, I warned you.

  • Will you listen to me now?

  • Don't worry.

  • The sound you heard was just an echo of your voice.

  • Let me explain what an echo is.

  • When we speak or laugh in a big empty hall, we hear our own sound repeatedly.

  • This is because our sound waves get reflected from the walls of the hall back to us.

  • The reflected sound that we hear is called an echo.

  • Hence, an echo is defined as the repetition of sound caused by the reflection of sound waves.

  • From a hard surface back to the listener.

  • Hey.

  • What are you doing?

  • Are you trying to hear an echo?

  • It is not that easy.

  • There are 2 ideal conditions for an echo to be heard.

  • When we speak or laugh, we hear our original sound at that moment.

  • The sensation of this original sound remains in our brain till 0.1 seconds.

  • This time is called the persistence of hearing.

  • When we utter sounds, some of our sound waves get reflected while some get absorbed.

  • If the reflected sound waves reach our ears before the completion of 0.1 seconds.

  • Then our brain does not perceive the original and reflected sounds as separate sounds.

  • They are interpreted as one sound.

  • Therefore, in order to hear two distinct sounds or an echo.

  • The time gap between the original sound and the reflected sound or echo should be at least 0.1 seconds.

  • This is the first condition for an echo to be heard.

  • Do you know when the time gap will be more than 0.1 seconds?

  • This gets us to the second condition for an echo.

  • The minimum distance between the speaker and the reflecting surface should be at least 17.2 meters.

  • When the distance is 17.2 meters and we start speaking.

  • Assume that the original sound reaches our ears at this time.

  • The reflected sound reaches our ears at this time.

  • Then the time interval between the reflected sound and the original sound will be equal to 0.1 seconds.

  • As a result, we will be able to hear an echo.

  • Alright.

  • Now, let us try and hear an echo in this room?

  • It is even bigger than the previous room.

  • Now, why can't we hear an echo?

  • This is because there are many soft furnishings like sofas, carpets, curtains, etc., in this room.

  • They absorb most of the sound waves.

  • As the sound waves do not get reflected, we are not able to hear an echo in this room.

  • Hence, one more thing to consider.

  • If we want to hear an echo, is that there should be minimal use of such sound absorbing materials.

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Smart Learning for All


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B1 中級 美國腔

為什麼我們會聽到回聲?| 我們為什麼會聽到回聲? (Why do we hear echoes? | #aumsum)

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    AumSum 發佈於 2021 年 01 月 14 日