Wave Behaviour
Sound waves react in different ways when they interact with an obstacle; reflection, refraction, absorption, and diffusion.
Reflection
Reflection is the process whereby part or the entire wave is returned when it encounters a boundary. For sound to be reflected, the object must be physically as large, or larger than the wave.
Low-frequency sound has a long wavelength and so can only be reflected by large objects. Higher frequency sound can be reflected by both small and large objects.
The reflected sound will have a different frequency characteristic than the direct sound if all frequencies are not reflected equally. Reflection is responsible for producing echo, reverb, and standing waves.
![Reflection](/application/files/2315/8670/0688/reflection.png)
Refraction
Refraction is the process where a waveform changes direction as it passes from one medium to another - the speed of the wave changes as this happens.
With sound waves, it is more common for the sound to refract when it encounters a change in air temperature. Since temperature decreases with height, the speed of sound also decreases with height.
![Refraction](/application/files/8815/8670/0688/refraction.png)
Diffraction
Diffraction is the bending of waves around small objects and the spreading out of a wave through small openings.
All waves tend to spread out at the edge when they pass through a gap or past an object. For spreading to happen, the wave must be larger than the object.
High-frequency waves have high directivity and can easily be blocked, whereas low frequencies have low directivity and spread far and wide.
![Diffraction](/application/files/1515/8670/0672/diffraction.png)
Absorption
Absorption is the loss of sound through an absorbent material. Reverb and standing waves can be controlled by adding absorption materials to a room.
![Absorption](/application/files/8615/8670/0669/absorption.png)