01 Jun Difference between diffusion and scattering
Diffusion and scattering-are they the same?
The expressions diffusion and scattering are often used interchangeably, but within acoustic terminology, they have different meanings. Most of our RPG products have measurements of both.
– Diffusion is an equal distribution of the different frequencies
– Scattering disperses the sound in a non-specular direction, thus the distribution in unequal
Diffusion is definitely better in a listening room because an equal distribution colors the sound far less. Almost anything can scatter the sound, but the distribution will vary at different frequencies and at different angles. Thus the sound becomes colored.
The graph below shows the difference between specular reflections (left), scattering (middle) and diffusion (right). The QRD diffuser was developed by Manfred Schröder, performing good diffusion and was an evolution over the poly diffuser.
Many of the products sold on the market today which are called diffusers are in reality scattering devices. There should be provided measurements (diffusion, scattering and absorption) of the product and a minimum of three diffusers together should be measured. Measuring one diffuser alone doesn’t give a correct picture of how they function together. When using several diffuser units, lobing will arise unless this is taking account for in the design.
The illustration below shows the difference between diffusion and scattering. Both from a diffuser. A diffuser will also perform scattering besides diffusion. The small dark box closest in the picture represents a speaker. The lines are mics that measures from different angles. In the upward middle the diffuser is placed.
Red graph shows the diffusion effect from a diffuser. We see that the diffusion is even and changes little in level at different angles.
Blue graph is the scattering. We can see how it’s distinguished from diffusion by focusing the energy to a greater degree in one direction. Scattering may be used to avoid specular reflections in a certain position by redirecting it somewhere else. It will however, not distribute the sound in a homogenous way like the diffuser. Take notice that this example shows good scattering where the energy is focused away from the listener, but a poor scattering would not necessarily do this.
Scattering is measured by the ISO 17497-1 standard.
Diffusion is measured by the ISO 17479-2 standard.