Materials, Building Components and Structure Testing
Scattering and Diffusion
Before we can discuss the subjects of scattering and diffusion we must understand how the terms are defined in the standards that are used to measure them. Specular reflections are those reflections that obey the tenants of Snell's Law. The angle of the specular reflection is always equal to the angle of incidence of the source energy.
Scattered energy is defined as the energy left over after subtracting specular energy loss from total energy loss (see Scattering Figure 1). Scattering is a measurement of random surface roughness not structured or large scale reflectors. The definition removes all surfaces that have a structural depth exceeding 1/16 of the sample size or surface size. Examples of this are large geometric reflectors such as pyramidals , cylindricals or structured seating areas. Basically all of these constructs are made up of surfaces that have large specular reflection surfaces and are exempt from this definition.
What is the "Scattering Coefficient":
The "Scattering Coefficient" is a parameter that is very much like the "Absorption Coeffcient". It describes the loss of energy in a diffuse field and is defined as the resultant of subtracting the specular reflected energy from the total reflected energy. The energy loss is then divided by the area of the sample and becomes a coefficient.
How is the scattering coefficient used?
Simulation programs used for architectural acoustics use coefficients to statistically calculate sound energy left in a room after a defined period of time. Until the last few years, the programs used only absorption coefficients to calculate the total absorption of energy in a room. Lately there has been an effort to include "scattering" in the calculations to simulate the loss of energy as well as the randomizing of reflections from the surfaces of the "room". (continued)