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Reflection

All objects (e.g. building, cylinder, polygon object, barrier, 3D-reflector) can be defined as reflective. An absorption or reflection coefficient can be assigned to their surface as a single number rating or as a spectrum.

The reflection calculation is carried out according to the image source method, i.e. additional image sources are taken into account for all possible ray paths until a pre-defined order of reflection is met.

The following figure illustrates how the 3rd order of reflection is constructed when sound propagates from source Q0 to receiver IP.

The maximum reflection order is specified via menu Calculation|Configuration, tab "Reflection".

Note

Objects will be considered as reflective only if their dimensions, projected into ray direction, in relation to the wavelength exceed a predefined value. For the simplified model based on A-weighted levels, the frequency 500 Hz is supposed per default.

In order to continue with the preceding example a reflective barrier is entered.

  • Select the object „barrier“ from the toolbox.

  • Enter the first polygon point via the keyboard at (x1,y1) = (130,140) and press the OK.

  • The next polygon point has the coordinates (x2,y2) = (170,140):

  • Confirm your input by OK and click the right mouse button to finalize the input-procedure. The barrier is now made of just a single segment.

  • Double-click onto the barrier to define its parameters. Enter on dialog Geometry a barrier height of 8 m.

  • All obstacles in CadnaA are non-reflective at first. To change this, click in the dialog Barrier on the option "Reflection Loss".

  • Select the reflective properties of the two barrier sides via the two file selector symbols . The directions "left" or "right" refer to the sides of the barrier when looking from first point to the last point of the barrier’s polygon line.

  • Choose from the dialog Reflection Type the option „Smooth Facade / refl. Barrier“ for either sides.

  • WIth those settings finalized the barrier’s dialog looks like shown below.

  • To include reflections in the calculation, the desired reflection order must be specified on the CadnaA-configuration. To this end, open via menu Calculation|Configuration the tab "Reflection" and select the 1st order of reflection.
  • Start the calculation by clicking the pocket calculator symbol.
  • In the representation, the ray of 1st order reflected at the barrier is shown besides the direct path:

  • Double-click on the reflected beam (displayed as an auxiliary polygon). The first part of the ID identifies this auxiliary polygon as a ray ("RAY"). The triple of numbers refers to the partial daytime level (Ld) transmitted via this ray path. The following detail "01" addresses the order of reflection of the ray.

  • Close the dialog and double-click on the direct path screened by the building. The detail also contains the transmitted daytime level and the reflection order (0th order = direct path). The letter „S" indicates that the ray is screened by at least one object on it’s ray path.

  • The protocol of calculation (menu Calculation|Protocol) lists the direct path in the first three line (column "Refl.", zero standing for 0th order of reflection, D/E/N) and in the further three lines the reflected ray (value "1" for 1st order of reflection, D/E/N).