# Diffraction of Sound: Exploring Why Wavelength Matters

• Misr
In summary, the conversation discusses the concept of diffraction and its effects on sound waves. It is explained that diffraction always occurs at boundaries, but is more noticeable with smaller objects. The amount of reflection and refraction depends on the difference in the speed of sound between two media. The conversation also includes a question about the effects of a big difference in speed, and a confusion about a concept illustrated in a diagram.
Misr
When the wavelength is bigger than an obstacle, then the sound waves bend around the obstacle.

so why
I can't imagine this at all

I read this page and watched the animations of it but it doesn't tell me the answer
http://www.acoustics.salford.ac.uk/feschools/waves/diffract.htm

reflection of sound takes place when the difference in the speed of the sound between two media is great,while refraction takes place when the difference in the speed of the sound between two media is small

why?

I think you are trying to categorise things too much. Diffraction always happens, at any boundary*. It is just more noticeable for a 'small' object.

Also, the effect of diffraction at the boundary between two 'transmissive' media will produce both a reflected wave and a refracted wave. The amount of reflection and refraction will depend on how big a change there is across the boundary and the angles involved.

* diffraction is just the result of all the waves adding up across the whole of the wavefront. When you shine light through a pinhole the resulting shape of the wave that gets through is very rounded. When you shine it through a doorway, much more light, in total, gets through but a tiny amount also 'leaks round the sides' with a very similar pattern at the very edge (90degrees) as from a pinhole. When we discuss reflection and refraction, we are usually discussing very wide wavefronts (big apertures) so we just ignore the off-axis ('diffracted') wave because it is so insignificant compared with all the energy going in the classically defined 'ray' direction.

But, for telescopes, for instance, we have refraction effects (focusing the image) plus diffraction effects (the ultimate blurriness of pictures of the Moon's surface etc.).

Okay,how about my second question?

reflection of sound takes place when the difference in the speed of the sound between two media is great,while refraction takes place when the difference in the speed of the sound between two media is small
Should I just accept this?

Misr said:
Okay,how about my second question?

Should I just accept this?

What do you mean by that?

Misr said:
Okay,how about my second question?

Should I just accept this?

The quote in that post is not correct. You always get both reflection and refraction for non normal incidence. You continue to categorize rather than try to understand.

Actually,I'm very confused about that
The quote in that post is not correct. You always get both reflection and refraction for non normal incidence. You continue to categorize rather than try to understand.
but most of the incident rays reflect and some rays refract due to the big difference in the speed of sound between air and water.That's what I mean
so what makes waves encounter more relection when difference in the speed of sound between air and water is big?

Another question :

[url]http://hyperphysics.phy-astr.gsu.edu/hbase/sound/imgsou/difr.gif[/url]

My problem about diffraction is here
what does we mean by "the wavelengths of sound are long enough to bend around the post"
Thanks in advance

##1) What is diffraction of sound?

Diffraction of sound is the bending of sound waves as they pass through an opening or around an obstacle. It is a fundamental property of all waves, including sound waves.

##2) Why does wavelength matter in diffraction of sound?

Wavelength is a key factor in diffraction of sound because it determines the amount of bending that occurs. The longer the wavelength, the more the sound wave will diffract, while shorter wavelengths will diffract less.

##3) How does the size of the opening or obstacle affect diffraction of sound?

The size of the opening or obstacle can greatly impact diffraction of sound. A smaller opening or obstacle will cause more diffraction, while a larger opening or obstacle will cause less diffraction.

##4) Can diffraction of sound be observed in everyday life?

Yes, diffraction of sound can be observed in everyday life. For example, when you hear someone speaking from around a corner, the sound waves are diffracting around the corner to reach your ears. The same principle applies when you hear someone's voice from behind a closed door.

##5) How is diffraction of sound used in practical applications?

Diffraction of sound is used in various practical applications, such as creating directional speakers, noise reduction in buildings, and improving the acoustics of concert halls. It is also an important concept in the field of ultrasound, used in medical imaging and sonar technology.

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