This calculator estimates the absorption coefficients of multi layer porous aborbers. Up to four absorbers can be modelled at once. The calculator's input parameters are split into three sections:

Global Parameters affect all absorbers. A reset button is provided which returns all global parameters (and parameter options) to their default values.

Parameter Options determine whether certain parameters appear in the Global or Absorber sections. For example, the angle of incidence can be set as a global parameter which affects all absorbers or it can be set to a different value for each absorber.

Absorber Parameters define the absorbers to be modelled. A reset button is provided for each absorber. Each absorber (except the first) also has a copy button which copies all parameters from the absorber directly above.

The parameters in each section are described below:

Global Parameters
Air temperature	The air temperature in degrees Celsius. The default value is 22°C.
Air pressure	The air pressure in Pascal. The default value is 101325 Pa.
Number of absorbers to be modelled	Between 1 and 4 absorbers can be modelled. The default number is 2.
Results format	The results can be displayed either as a graph, or as a detailed analysis including information such as surface impedance, angle of propagation, etc.
X axis	Where results are to be displayed as a graph, absorption coefficient can be plotted against a number of alternative variables on the X axis. By default, absorption coefficient is plotted against frequency.
X range	These fields set the X axis range to be displayed when the results format is set to "Graph".
X scale	If the X axis variable is Frequency then the scale can be set to either Logarithmic or Linear. In all other cases the Logarithmic option is disabled.
Resolution	The resolution can be set to High, Medium or Low. Higher resolution gives a smoother graph but results in longer calculation times.
Frequency	This field sets the frequency at which the analysis is performed. This option is not available if a graph is to be plotted with frequency on the X axis.
Random incidence	If this box is checked, the absorption coefficient is calculated for random incidence. This option is not available when the results format is set to "Detailed Analysis" or if a graph is to be plotted with angle of incidence on the X axis.
Angle of incidence	The angle of incidence can be set from 0° to 90°, where 0° represents normal incidence. This field is disabled when random incidence is selected and is also not available if a graph is to be plotted with angle of incidence on the X axis.
Model	This parameter sets which model is used to estimate the properties of porous absorbent layers. The default model is "Delany and Bazley".
Parameter Options
Angle of incidence	When set to "Global", the angle of incidence appears as a global parameter and is applied to all absorbers. When set to "Absorber", the angle of incidence can be set individually for each absorber.
Analysis frequency	When set to "Global", the frequency appears as a global parameter and is applied to all absorbers. When set to "Absorber", the frequency can be set individually for each absorber. This option has no effect when the results format is set to "Graph".
Model	When set to "Global", the model appears as a global parameter and is applied to all absorbers. When set to "Absorber", the model can be set individually for each absorber.
Absorber Parameters
Layer	This field sets the type of layer as follows: Not used - The layer is not included in the model. Air - The layer is an air gap. Porous absorbent - The layer is a porous absorbent.
Thickness	The thickness of the layer in mm.
Flow resistivity	The flow resistivity of the layer in Pa.s/m2.
Random incidence	See global parameters above.
Angle of incidence	See global parameters above.
Frequency	See global parameters above.
Model	See global parameters above.