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Pass-By Level

In CadnaA, the time signal of the sound pressure level at a receiver point due to the pass-by of an individual vehicle with a predefined emission can be calculated for roads - but also for railways or line sources.

Via the time signal it can be assessed - for example:

  • whether a noise mitigation measure (e.g. a barrier) causes a sufficient level reduction,
  • the level reduction due to an absorptive cladding of a reflecting façade of a building, or
  • the amount the resulting level of vehicles passing by is reduced when an ordinary road is converted into a speed-reduced zone.

In the following example the pass-by level at a building’s façade is studied.

Entering Objects

  • Enter a road with several polygon points with the following emission data for CNOSSOS-EU:
    • road width: 5 meters using the CNS_01 Reference Road Surface
    • MDTD = 20000 vehicles/24 h and road type „national“
  • Enter a building with a height of 10 meters on a side of the road.
  • Select the command Object Snap (Options menu) and enter a distance of 0.05 m and a snap radius of 10 pixels.
  • Insert a receiver at the lateral side of the building.
  • Name the receiver point by RCVR 1.
  • Start the calculation by clicking on the pocket calculator symbol .

Building alongside of a road with a receiver partially screened by the building

Calculating the Pass-by-Level

  • Click with the right mouse button on the road axis and select the command Pass-by Level from the context menu.

The dialog Pass-by Level is opened. The level during a pass-by depends on:

-  the select receiver point,
-  the source type (car, truck), and
-  the speed (km/h).

Since just one receiver point is available in the example, this is selected automatically.

  • Select the entry „light" from the list box „Source Type“.

The speed dependent sound power levels of an individual vehicle in dB(A) are based on the emission data of RLS 90.

  • Enter 4 meters as length of the source.
  • Keep the speed of 100 km/h and the sampling time of 0.1 s (interval between the individual positions of the source).
  • Click on the button OK to display the time dependent pass-by level.

Pass-by Level at a receiver partially screened

CadnaA displays the level at each sampling position along the road in the Pass-By Level dialog’s title.

  • By moving the mouse cursor within the window the levels at a certain time can be displayed.

With this example, the level rises at the receiver until the closest approach of the source and decreases due to the screening effect caused by the building’s edge.

Auralisation

The sound during a pass-by can be heard through a loudspeaker connected to the computer.

  • Click on the dialog Pass-By Level on the command Auralisation|Properties.
  • Select as an acoustic source type "Road".
  • Activate the option "3D-Auralisation". In this case, the Doppler effect is included with vehicles approaching and departing.

  • Keep the settings for „Listening Direction at Receiver“ and click OK.
  • Start the animation at default speed (1x) by clicking on the menu item Animation.

The animation is started while the signal at receiver 1 is reproduced via loudspeaker (and the audio output connector of your PC).

Record Video

The change of the level grid when the source is moving can be saved as a video file and replayed with a suitable software later on (e.g. MS-Windows Media Player).

  • Define a calculation area (symbol ) around the road and the building with the receiver point.

  • In addition, define a section (symbol ) around the calculation area and name it "A1".

  • Specify a grid spacing of 2 by 2 meter (menu Grid|Properties).

  • Again, select the command Pass-by Level from the context menu of the road, enter again a length of 4 meters and keep all other settings.
  • Select the section "A1" in the lower part („Video-Options“) of the dialog and click on the button "Video".
  • Enter a name for the video file to be generated (e.g. "road_1") and click OK.
  • Select a video codec and click OK.

Note

The contents of the list depends on the video codecs installed on your PC.

CadnaA starts the grid calculation for every sampling position of the source and saves the moving grid as a frame in the video file.

  • Double-click on the video file in the respective directory to replay it.

Two video-frames with a moving source and a building

Further Options

Information on further options available on the dialog Pass-By Level please refer to the CadnaA-Reference Manual, chapter Pass-By of individual Vehicles.