Attenuation, Absorption and Scatter

 Attenuation, Absorption and  Scatter

Attenuation

When
sound waves are emitted they spread out in all directions and therefore their
intensity reduces with
distance travelled in accordance with the Inverse Square Law. The strength of
intensity is, however, also reduced
or attenuated by two other mechanisms; absorption and scatter.


 Absorption

A sound wave propagates by the vibration
and collision of molecules. Such molecular movements require energy
and also give out energy
in the form of heat due to friction. This energy originates in the sound wave. The sound wave is therefore weakened
due to absorption of its energy by the molecules of the medium it travels through.


  • Absorption decreases as sound
    frequency decreases.

 Scatter

Steel, and metals in general, have a
grain structure. Grain boundaries refract and reflect a small proportion of the incident
sound wave and so tend to scatter
it. As a result, less of the sound beam continues in the original direction. 

  • Scatter decreases as sound
    frequency decreases.
  • Scatter decreases as grain size decreases.




When sound waves are emitted they spread out in all directions and therefore their intensity reduces with distance travelled in accordance with the Inverse Square Law. The strength of intensity is, however, also reduced or attenuated by two other mechanisms; absorption and scatter. A sound wave propagates by the vibration and collision of molecules. Such molecular movements require energy and also give out energy in the form of heat due to friction. This energy originates in the sound wave. The sound wave is therefore weakened due to absorption of its energy by the molecules of the medium it travels through. Steel, and metals in general, have a grain structure. Grain boundaries refract and reflect a small proportion of the incident sound wave and so tend to scatter it. As a result, less of the sound beam continues in the original direction.
Attenuation, Absorption and  Scatter


Leave a Comment