Reflection of Sound

Bertleja S, Academic Content Writer for Physics at Edumarz.

     Bouncing back of sound waves from the surface is called Reflection of Sound.

  • Similar to reflection of light.

  • Follows laws of reflections.


  • The angle of incidence = the angle of reflection 

  • The incident sound wave, the reflected sound wave and the normal at the point of incidence lie on the same plane.

Fig 1: Laws of reflection of sound waves




  • A repetition of sound produced by the reflection of sound waves from a wall, mountain, or other obstructing surface is called an echo. 

  • The sound persists even after the source of the sound has stopped vibrating. 

  • The time interval between the original sound from the source and the reflected sound should be at least 0.1s to effectively hear a distant echo.

  • The speed of sound in air at 20°C is 344 ms-1


          Velocity = Distance Travelled

                      Time taken


             =  2d


        2d = 344 × 0.1

          d = 17.2 m

  • The minimum distance between the obstacle and the source of sound is 17.2 metre. 

Multiple Reflection of Sound:

     Multiple reflection of sound is the reflection of light back and forth through reflecting surfaces several times.

Applications of Multiple Reflections of Sound Waves:

  1. Reverberation

  2. Stethoscope

  3. SONAR

  4. Megaphones



  • The persistence of sound that is caused by multiple reflections is called reverberation. 

  • The duration for which the sound persists is called reverberation time.

  • In an auditorium or big hall, high reverberation will greatly affect the quality of sound heard. This can be avoided by covering the walls and ceilings with sound-absorbent materials

  • The ceilings of a big hall or auditorium are curved. This will minimise the spreading of sound waves in all directions and also enhances the uniform distribution of sound throughout the hall so that a person sitting at any position in the hall can hear the sound clearly.


Fig 2: Curved ceiling of a conference hall


  • Principle: Multiple Reflections

  • Multiple reflections take place in the rubber tube that connects the chest piece and the ear piece. 

  • The sound of heart beats or any sound produced by internal organs reaches the ear piece through the rubber tube after multiple reflections.

Fig 3: Stethoscope and multiple reflection of signal in a rubber tube

SONAR ( SOund Navigation And Ranging) :

  • SONAR technique uses the reflections of sound waves in water to locate the position or motion of objects.

  • Similarly, bats and dolphins use the SONAR principle to locate objects in the darkness.


  • Megaphones, horns and musical instruments like trumpets are designed to send the sound from source after multiple reflections towards a particular direction without allowing the spreading of sound in all directions.


Fig 4: Multiple Reflection of Sound in Megaphone


  • Echoes may be heard more than once due to multiple reflections.

  • The rolling of thunder is caused by the multiple reflections of the sound of lightning having reflecting surfaces such as clouds and the earth’s surface.

Leave a Reply