The exterior field pressure is evaluated using the exterior field operator (the name is defined in the Exterior field variable name input field, the default is pext).
To evaluate the pressure in a point (x0,y0,z0), simply write pext(x0,y0,z0). To evaluate the sound pressure level in the same point, it is advantageous to use the subst() operator and write, for example, subst(acpr.efc1.Lp_pext,x,x0,y,y0,z,z0).
An example of this is given in the Loudspeaker Driver — Frequency-Domain Analysis tutorial model from the Acoustics Application Libraries.
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In older versions of COMSOL Multiphysics the Exterior Field Calculating feature was called Far-Field Calculation. The Exterior Field Calculating has an improved GUI and uses the full integral as default. In acoustics the amplitude and phase of the pressure signal are in most cases necessary and evaluation is often not performed in the true far field (beyond the Rayleigh radius of radiating bodies).
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The ppr() operator is not added when the exterior field calculation is performed on an external boundary or a boundary adjacent to a perfectly matched layer (PML) domain. In the latter case, the down() or up() operator is automatically added in order to retrieve values of variables from the physical domain only.
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