Acoustical Diffraction Near The Earth's Surface
In the case of sound waves travelling near the Earth's surface, the waves are diffracted or bent as they traverse by a geometric edge, such as a wall or building. This phenomenon leads to a very important practical effect: that we can hear "around corners". Because of the frequencies involved considerable amount of the sound energy (on the order of ten percent) actually travels into this would be sound "shadow zone". Visible light exhibits a similar effect, but, due to its much higher frequency, only a minute amount of light energy travels around a corner.
A useful branch of acoustics dealing with the design of noise barriers examines this acoustical diffraction phenomenon in quantitative detail to calculate the optimum height and placement of a soundwall or berm adjacent to a highway.
This phenomenon is also inherent in calculating the sound levels from aircraft noise, so that an accurate determination of topographic features may be understood. In that way one can produce sound level isopleths, or contour maps, which faithfully depict outcomes over variable terrain.
Read more about this topic: Atmospheric Diffraction
Famous quotes containing the words earth and/or surface:
“All places are alike,
And every earth is fit for burial.”
—Christopher Marlowe (1564–1593)
“We’ve forgotten what it’s like not to be able to reach the light switch. We’ve forgotten a lot of the monsters that seemed to live in our room at night. Nevertheless, those memories are still there, somewhere inside us, and can sometimes be brought to the surface by events, sights, sounds, or smells. Children, though, can never have grown-up feelings until they’ve been allowed to do the growing.”
—Fred Rogers (20th century)