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Science_Lab_Yellow / Lesson 6: Sounds Bounce

Sounds Bounce

  What will we be learning today?

 

  • In this lesson, we are going to learn all about how is sound bounce.


Do Sounds Bounce?

 

  • A sound hitting a towel will sound different from the same sound hitting a metal sheet. Why? A sound wave does not act the same way when it hits a hard, smooth surface as when it hits a soft, textured surface.

 


  • The pictures below show what happens when sound waves come into contact with a surface. When a sound wave hits a surface, some of its energy bounces off the surface. The bouncing of a sound wave off a surface is called reflection. However, not all of the sound wave reflects off the surface. Some of the wave's energy enters the surface, and part of the sound disappears. The disappearance of a sound wave into a surface is called absorption.




    Compare the crack of the bat when the ball and bat meet with the sound when the ball hits the glove.



When a sound wave is absorbed, its energy is changed into heat energy. Sometimes not all of the energy that enters a surface is absorbed. Part of the energy of the sound wave may also travel through a surface and come out the other side-when you hear a sound through a wall.


How much of the sound wave's energy is reflected or absorbed depends on the kind of material of the surface. When sound waves hit a hard, smooth surface such as the wall around the racetrack, much of the sound wave's energy is reflected. However, when sound waves hit a soft, textured surface such as a towel, less of the sound wave's energy is reflected and more is absorbed.


How Reflection and Absorption Affect Concert Halls

 

  • Designing concert halls has always been a tricky business. To get the "right" sound, engineers try to get a good balance of reflection and absorption. Too much reflection results in an empty, hollow sound. Too much absorption deadens the music.

 


When the London Music Hall was built in 1871, the hall was considered to be one of the great places in the world to hear music. By the 1930s listeners complained that the music did not sound good anymore. Sound engineers were baffled. Nothing in the concert hall had changed since it was built, over 60 years earlier.


Finally, an explanation was found. The concert hall may have stayed the same, but its audience had changed. Most importantly, women were no longer wearing the billowing, layered, sound-absorbing gowns that had been popular earlier. The new styles were shorter and simpler, and didn't absorb sound as well. Overall they changed the balance of reflection and absorption of sound in the room.