A new scattering method that combines roughness and diffraction effects

Abstract

Most of today's room acoustics programs make use of scattering coefficients which are used in order to describe surface scattering (roughness of material) and scattering of reflected sound caused by limited surface size (diffraction). A method which combines scattering caused by diffraction due to typical surface dimensions, angle of incidence and incident path length with surface scattering is presented. Each of the two scattering effects is modeled as frequency dependent functions. The benefits are two-fold:• Separating the user specified surface scattering coefficient from the room geometry makes it easier for the user to make good gestimates of the coefficients that will be in better agreement with the ones that can be measured. In many cases a scattering coefficient of say 5% for all smooth surfaces may be sufficient.• Scattering due to diffraction is distance and angle dependent and as such it is not known before the source and receiver are defined, and the actual 'ray-tracing' or image source detection takes place. An example on this is that a desktop will provide a strong specular component to its user whereas it will provide scattered sound at remote distances.

Effects of the Distance from a Diffusive Surface on the Objective and Perceptual Evaluation of the Sound Field in a Small Simulated Variable-Acoustics Hall

“…This model complies with the definition of the scattering coefficient based on ISO 17497-1, which defines it in a quantitative way as the fraction of the non-specularly reflected energy. On the contrary, the VM is based on the linear interpolation of the specular and diffuse reflection [45], i.e., the direction of a reflection vector is calculated by adding the specular vector scaled by a factor (1-s) to a scattered vector following a certain direction that has been scaled by a factor s. This is the basic concept implemented in Odeon [41,46], named "vector-based scattering", where the scattered vector follows a random direction, generated according to the Lambert distribution. Thus, the scattered reflections are also implemented from a qualitative point of view, which makes this model a more realistic approximation of the diffusive surface directivity.…”

“…This combination leads to the "reflection-based scattering coefficient" sr [41,46], which can be calculated from: [44]; (e) and (f) RAPDFs for s = 0.75 and s = 0.05 [44]; (g) Simplified reflection model for 3D modeled periactes.…”

“…This combination leads to the "reflection-based scattering coefficient" s r [41,46], which can be calculated from:…”

“…This type of situation gives rise to scattering that increases with frequency and can be inserted by the user based on scattering coefficient measurement databases, i.e., user-based scattering. In Odeon, typical measured scattering coefficient frequency functions [41,46] are used to expand a mid-frequency scattering coefficient input by the user to all frequency bands. This means that only one input value for the scattering coefficients needs to be specified for a surface at a middle frequency around 707 Hz (average of 500-1000 Hz bands).…”

Overview of geometrical room acoustic modeling techniques

“…They adjusted the specular reflection strength to obtain an asymptotic high-pass filter effect and assigned the reduced energy to scattering. 119 …”