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Radiation by the Stack’s Shell

The sound radiation from the chimneys surface is particularly relevant with light steel chimneys which may have a small sound reduction index or transmission loss. In CadnaA this radiation component is considered by a vertical line source in the chimney's axis.

  • First, zoom in using the zoom-in tool (e.g. to scale 1:100).
  • Select the line source and enter a short line nearby the cylinder’s center point.

Cylinder with a short line source near the cylinder’s axis

  • Double-click on the line source and click the button "Geometry".
  • Activate the option "Last Point“ and enter a height of 19.95 m for the last point.
  • Close the dialog Geometry and activate the option „Trans.Loss“ on the line source’s dialog.
  • Enter an interior level of 90 dB(A) and a transmission loss of 30 dB.
  • The radiating surface of the cylinder results from: \(2\pi*r*l = 2\pi * 3 * 20 = 377 m^2\). Enter this value into the input box „Area (m²)“.

Data of the line source

  • Now, select a scale of 1:1000.
  • Double-click on the vertical grid and start the calculation via click on button:

When radiating from the opening and from the cylinder the resulting receiver level is 55.5 dB(A), in this example.