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Pre-defined Directivities

From the list box on the dialog Directivity predefined directivities can be selected. Available are e.g. the following directivities (literature links see chapter Literature in the CadnaA-reference manual):

  1. radiation from building elements according to OEAL 28 (1987 ÖAL24-2008 and amendment Feb. 2001 ÖAL28-1987),

  2. radiation of openings according to OEAL 28 (ed. Dec. 1987 ÖAL28-1987), and

  3. radiation of chimneys.

Directivity vector, Automatic Direction

The forward direction (direction 0°) of the directivity vector depends on the source type:

  • Point source: The auto-vector points in the direction of the normal vector of the reflecting surface of an object nearby.
  • Line source: The vector points in the direction of the line (seen from first to last point).
  • Area source: The vector points in the direction of the normal vector of the area (right-hand rule).
  • Vertical area source: The vector points to the right when looking from first to last polygon point.

Example: point source in front of a building

In a following example, the use of a predefined directivity is explained using a point source in front of a building.

  • Enter a building with 10 m side length (scale 1:500).
  • Enable the feature Object Snap with a snap radius of 10 pixels at a distance of 0.05 m.
  • Choose the Point Source from the toolbox and click within the snap radius in front the building’s right facade, approximately the middle. The point source is set at a distance of 0.05 m after that in front of the facade.
  • If you double-click on the point source’s border the dialog is displayed.
  • Enter an A-weighted sound power level of 100 dB(A) and a value of 3 dB for "K0 without ground".
  • Click on button „Directivity“ and select from the list box the predefined directivity „Element“. Keep the setting directivity "Automatic Direction".
  • Draw a calculation area around the building and calculate the grid using a grid spacing of 1x1 m (menu Grid|Properties) as a line grid (menu Grid|Appearance).

Point Source at a building with directivity „Element“, automatic direction