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19 February 2014

I Can Hear The Bells

Dear Senserely Yours,

I have homework from school about sounds in the environment and I'd like to ask your help. Every Saturday morning, my mom and I visit the church in our village for the early mass. As soon as the mass ends, the church bells ring. I noticed that the sounds they make create different echoes. What causes these echoes? and how is it possible that sound is replicated over and over? I would like to know. 

-HomeworkHelpee



Dear HomeworkHelpee,

Thanks for sending in your letter! We're glad to help you understand the sounds you perceive in your environment. First we have to know what produces sound and how does it travel to our ears. Sound is produced in sound "waves" like those on the beach. However, these sound waves are not visible to our eyes.This is because these "waves" are actually changes in the pressure in the air. Vibrations created by objects changes the air pressure around it and this travels through the air.Constant vibration makes the air more condensed and loose alternately through the processes of condensation and rarefaction (Goldstein, 2010).

In the environment, there are two types of sound which are direct and indirect sound. According to Goldstein (2010), direct sound is sound that travels a straight path directly into your ears. This normally happened in open spaces such as the outdoors. Indirect sound on the other hand is sound that bounces of or is reflected off a surface of an object before it reaches your ears. It is more common on indoor spaces since sound bounces off more objects while indoors such as the floor, the walls, and the ceiling. In outdoor environments, indirect sound can come from trees or nearby buildings.

An echo is a replication or repetition of sound. In outdoor environment, this replication of sound is achieved when sound waves you produce bounce off a surface, such as mountains or canyons, and are reflected back to your ears (Marshall, 2000). When this happens, the distance between the source of the sound and the surface it reflected upon creates a delay in the travel of sound. The perception of sound usually lasts for only 0.1 seconds in our memory ((The Physics Classroom, n.d.) This creates the effect of sound replicating itself because it creates a small delay between the perception of the original sound and the reflected sound.

Another way echoes are created is through long reverberation time. Reverberation time is the amount of time it takes for a sound to decrease to 1/1000th of its original pressure (Goldstein, 2010). Usually, the delay between the original sound and the reflected sound is less than 0.1 seconds.This means that it creates the perception that there is no delay but rather creating a prolonged sound. However, there are times when the reverberation time varies. Goldstein explained that when the reverberation time lasts for too long, the sound becomes muddled rather than prolonged. In cases where reverberation time is extremely long, echoes are created inside rooms.

So these are how echoes are created. I hope we were able to help you understand how sound travels in our environment, both indoors and outdoors, and how echoes are created in these environments. Good luck with your homework!

Senserely yours,
Dea

References:
Goldstein, E.B. (2010). Sensation and Perception. Belmont, California: Wadsworth, Cengage Learning.
Marshall, B. (2000). How Radar Works.  Retrieved from http://science.howstuffworks.com/radar.htm.
The Physics Classroom (n.d.). Echo vs. Reverberation. Retrieved from http://www.physicsclassroom.com/mmedia/waves/er.cfm.

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