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Calculate Free Field Simulation

This calculation option calculates for a selected source group the level for a semi-free field at all linked and active receivers, without requiring to manually apply a retrofitting of the room surfaces in advance (i.e. fully sound-absorbing walls on a reflective floor).

Background

When working on projects with machinery there is a need, appearing regularly, to perform a calculation for semi-free field conditions as being defined by measurement standards. For example, this applies in situations where just the sound pressure level SPL has been measured at receivers in the vicinity of a machine while the corresponding sound power level PWL/LWA is, however, unknown. In these situations, the sound power level PWL/LWA of the machine/s or plant components have to be estimated applying appropriate methods. Subsequently, using this free field simulation it can be studied whether the measured sound pressure levels SPL in vicinity of the machine or machine group match the calculated ones (at least as a first approximation).

Procedure

The following steps are required:

  • The sub-sources making up the machine model, and also the associated measuring points (receiver points) in the vicinity of the machine must be arrange within a common group. The easiest way to achieve this is by using the ObjectTree in CadnaR (see ObjectTree).
  • When there are several machines in the project file, each machine (including the associated receivers) must be arranged in separate groups.
  • When selecting this command, the dialog Calculation Freefield Simulation is opened enabling to select a source group defined in the ObjectTree.

Dialog Calculation Freefield Simulation

  • Click on the ObjectType icon to open the dialog Select.

  • Select one of the predefined source group.

  • After clicking OK, the free-field simulation is launched. The results are displayed in the receivers having been assigned to the source group.
  • By reselecting a different group the free-field simulation can be run successively for all existing source groups.