ODEON 4.2 he following features:Angular absorption. Early scattered rays. Open GL (Acoustic colors). Extended modelling language.
Sound absorbing materials have an angle dependent absorption. Although little is known about this angle-dependent behaviour, Odeon has applied the approximation described in Applied Acoustics 38 (1993), see the list of publications. In this model the impedance of the surface is assumed to be real and independent of the angle of incidence, i.e. locally reacting. The angle dependency comes from the field impedance, which is also dependent on the size of the reflecting or absorbing surface.
The example beow of the absorption coefficients for a surface representing persons on soft chairs and a large area of 1000 m2. The statistical absorption coefficient ‘stat.’ is the input for calculating the absorption coefficient at various angles of incidence. Near normal incidence (0°) the absorption is higher and near grazing incidence (75°-90°) the absorption is lower that the statistical value. The result is that a surface with a material having a high absorption coefficient, may actually create relatively strong reflections when exposed to sound near glazing angle. In the Room setup menu the Angular absorption can be disabled or applied either to all materials or to soft materials, only. In this context ‘soft materials’ means cases with a statistical absorption coefficient > 0.5. This is the recommended default, as there is negligible effect of applying the angular absorption to cases with lower absorption; so some calculation time can be saved by this choice. In the Room setup menu the Angular absorption can be disabled or applied either to all materials or to soft materials, only. In this context ‘soft materials’ means cases with a statistical absorption coefficient > 0.5. This is the recommended default, as there is negligible effect of applying the angular absorption to cases with lower absorption; so some calculation time can be saved by this choice. The method also gives the pressure reflection factor, which can take values between -1 and +1. A negative reflection factor means a 180° phase shift of the reflected sound. In Odeon this is applied in the calculation of the binaural room impulse response (BRIR) if the ‘phase shift at surfaces/filterphase’ is selected in the Auralisation setup, see the second picture below of the menu.
In order to handle the scattering properties of surfaces for early reflections the idea of Early Scattered Rays is introduced. This should be seen as an extension of the classical Image Source Method for early reflections. The reflected energy is divided into a specular part and a diffuse part. The scattering coefficient of the surface then defines the ratio of reflected energy that is handled as diffuse reflection, and the remaining part comes as a specular reflection.
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The concept of acoustic colours is introduced to visualize the acoustic properties of materials in a room model. Darker colour surface material means more absorption, lighter colour surface material means more reflecting surfaces, red means that materials reflects relatively more low frequencies and blue means that the surface reflects relatively more high frequencies. In this way the acoustic reflection/absorption is transferred to reflection/absorption of light in order to make the visualisation more intuitive to the user.
It is possible in version 4.2 to model shapes like Box, Cone, Cylinder, and Dome using a single line of code. Coordinate manipulation is extended in order to allow flexible use of these shapes and reuse of other geometries.