Image source 25/22/2023 ![]() This suggests that the image model should be used only for very early reflections, where most energy is not scattered, and a secondary model used to compute late, diffuse reflections. Kuttruff shows that, though the earliest reflections may be largely specular, after a few reflections the large majority of sound energy becomes diffuse. The conversion from incoming energy to scattered energy is unidirectional, so repeated reflections cause the ratio of scattered to specular energy to increase monotonically. Consider that, once scattered, sound energy cannot become un-scattered. The image-source model is not capable of modelling this phenomenon, though this is not particularly problematic. Some energy will be randomly diffused in non-specular directions. In the real world, not all energy is perfectly reflected at a boundary. The frequency response of the signal from each image source will additionally be modified depending on the characteristics of each boundary in which that source was reflected. The total impulse response (i.e. sound pressure against time) is found by summing the signals from each source, delayed and attenuated appropriately depending on the distance between that source and the receiver, which is equivalent to the length of the specular reflection path. Figure 1: Image sources are found by reflecting the source position in a boundary.Īll sources, original and image, emit the same impulsive source signal at the same time. A ray which is reflected from several boundaries is represented by a “higher-order” image-source, which has been mirrored in each of those boundaries in turn. If the source is reflected in a single boundary, this represents a first-order reflection. ![]() This new “image” source now represents a perfect reflection path, in that the distance along the straight line between the receiver and the image source has the same length as the path from the real source to the receiver, reflected in the boundary. This source is located on a line perpendicular to the wall, at the same distance from it as the original source, as if the original source has been “mirrored” in the surface (an example is shown in fig. When a ray is reflected, it spawns a secondary source “behind” the boundary surface. Rays are perfectly reflected at boundaries. The energy in each ray decreases with \(1/r^2\), where \(r\) is the total distance that the ray has travelled. Sound energy travels at a fixed speed, corresponding to the speed of sound, along these rays. This process is simplified by assuming that sound propagates only along straight lines or rays. ![]() The image-source method aims to find the purely specular reflection paths between a source and a receiver. Image-source Model Background Basic Method
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