![images of diffraction of sound images of diffraction of sound](https://img-cdn.thepublive.com/fit-in/1280x960/filters:format(webp)/bnn/media/media_files/642c797373c8caaa838e5b1983fb1890ac888809fc624be77e2fac9086e9fd42.jpg)
Wavelengths for visible light range from 400 (violet) to 700 nm (red): hence, it would be possible to fit about 5,000 of even the longest visible-light wavelengths on the head of a pin! Light waves, on the other hand, have a wavelength, typically measured in nanometers (nm), which are equal to one-millionth of a millimeter. The waves by which sound is transmitted are larger, or comparable in size to, the column or the door-which is an example of an aperture-and, hence, they pass easily through apertures and around obstacles. Longitudinal waves radiate outward in concentric circles, rather like the rings of a bull's-eye.
![images of diffraction of sound images of diffraction of sound](https://image3.slideserve.com/6007793/sound-diffraction-l.jpg)
Sound travels by longitudinal waves, or waves in which the movement of vibration is in the same direction as the wave itself. The reason for the difference-that is, why sound diffraction is more pronounced than light diffraction-is that sound waves are much, much larger than light waves. But, if you moved away from the door and stood with your back to the building, you would see little light, whereas the sound would still be easily audible. And if you stood right in front of the doorway, you would be able to see light from inside the concert hall.
![images of diffraction of sound images of diffraction of sound](https://cdn.shopify.com/s/files/1/0597/1004/6384/files/How_7.1_Surround_Sound_Works-1_480x480.jpg)
The sound quality would be far from perfect, of course, but you would still be able to hear the music well enough. Suppose, now, that you had failed to obtain a ticket, but a friend who worked at the concert venue arranged to let you stand outside an open door and hear the band. Light waves diffract slightly in such a situation, but not enough to make a difference with regard to your enjoyment of the concert: if you looked closely while sitting behind the post, you would be able to observe the diffraction of the light waves glowing slightly, as they widened around the post. But you have little trouble hearing the music, since sound waves simply diffract around the pillar. You cannot see the band, of course, because the light waves from the stage are blocked. Imagine going to a concert hall to hear a band, and to your chagrin, you discover that your seat is directly behind a wide post. Diffraction determines the direction in which most sound will be radiated, an important factor for the acoustical engineers who work to make them as quiet as possible.C OMPARING S OUND AND L IGHT D IFFRACTION The white region is a cross-section of the front part of an aircraft engine, the sound wave is produced by the turbofan.
![images of diffraction of sound images of diffraction of sound](http://salfordacoustics.co.uk/wp-content/uploads/2019/01/sound.png)
The animation below shows another example of diffraction. Thus, this solution for noise reduction is efficient only if the houses are located within the shadow region of the sound barrier. It is characterised by low noise levels due only to the acoustic diffracted wave. A shadow region is observed just behind the barrier (bottom right of the animation). Interference patterns due to the superposition of the incident wave and the diffracted wave are clearly seen just before the barrier (bottom left of the animation). The animation below illustrates how a travelling wave emitted from the upper left corner by, say, an aeroplane is diffracted by a sound barrier erected to shield homes from the traffic noise. An example of diffraction phenomena is given by the spreading of waves around an obstacle. Diffraction occurs if a wave encounters an object and if the wavelength is of the same size (or greater than) the object size. The spreading of waves when they pass through an opening, or around an obstacle into regions where we would not expect them, is called diffraction.