Wave Behaviour
Sound waves interact with obstacles in four ways: reflection, refraction, absorption, and diffusion. Learn how these phenomena shape our auditory experiences.
Reflection
Reflection is the process whereby part or all of a wave is returned when it encounters a boundary. For sound to be reflected, the object must be as large or larger than the wavelength of the wave.
Low-frequency sound has a long wavelength and 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 equally reflected. Reflection is responsible for producing echo, reverb, and standing waves.
Refraction
Refraction is the process where a waveform changes direction as it passes from one medium to another, causing a change in speed.
With sound waves, it is more common for the sound to refract when it encounters a change in air temperature. As the temperature decreases with height, the speed of sound also decreases.
Diffraction
Diffraction is the bending of waves around small objects and the spreading out of waves through small openings.
All waves tend to spread out at the edges when passing through a gap or around an object. For spreading to occur, the wavelength must be larger than the object.
High-frequency waves, which have high directivity, can be easily blocked, while low-frequency waves, with low directivity, spread over larger areas.
Absorption
Absorption is the loss of sound energy through an absorbent material. Reverb and standing waves can be controlled by adding absorption materials to a room.
