Dedicated Acoustics Plots for Postprocessing
Dedicated acoustics postprocessing functionality exist to plot responses, transfer functions, directivity patterns and more. They require the Acoustics Module license.
In this section:
Far-Field Plots (Spatial Response)
Evaluating and plotting the acoustic pressure around radiating objects and sources is essential for the development of several acoustic devices. This is known as the spatial response. Application areas range from underwater acoustic transducers and loudspeakers, to determining the spatial sensitivity of microphone systems (for example, using reciprocity). Using the Far-Field Calculation feature can help to reduce the computational domain while still being able to determine the pressure and thus the spatial response in the near-field to far-field. The Far Field plots are specially designed for easy evaluation of the far-field variables, that is, the acoustics far-field pressure and the far-field sound pressure level.
In the Far Field plots the far-field variable (pressure or sound pressure level) is represented in a polar plot for a selected number of angles. Data is retrieved on an evaluation circle in 2D, 2D axial symmetry, or 3D. The angle interval and the number of angles can be manually specified. The evaluation circle origin, orientation, and radius can be specified as well as the reference direction. The evaluation circle can be visualized using a Preview Evaluation Plane functionality. There is also a built in option to calculate the Beam Width of the plotted data. A 3D polar plot also exists where the data is evaluated on a sphere. For 3D far-field plots you also specify an expression for the surface color.
Figure 2-5: Example of a 2D and 3D far field plot from the Bessel Panel tutorial model.
The main advantage with the far-field plot, as compared to making a line graph, is that the unit circle/sphere that you use for defining the plot directions, is not part of your geometry for the solution. Thus, the number of plotting directions is decoupled from the discretization of the solution domain.
Default Far Field plots are automatically added to any model that uses far-field calculations.
For a 3D example, see Bessel Panel: Application Library path Acoustics_Module/Tutorials/bessel_panel.
For a 2D axisymmetric example, see Cylindrical Subwoofer: Application Library path Acoustics_Module/Tutorials/cylindrical_subwoofer.
Far Field and Results Analysis and Plots in the COMSOL Multiphysics Reference Manual
Grid and Parametrized Data Sets
Another way of evaluating and depicting the far field is by using either the Grid 2D, the Grid 3D, the Parametrized Curve, or the Parametrized Surface data sets. Both types of data sets allow the evaluation of global quantities, like the far-field variables, outside of the computational domain (outside of the mesh).
The far field is depicted in several ways in the model Piezoelectric Tonpilz Transducer: Application Library path Acoustics_Module/Piezoelectric_Devices/tonpilz_transducer.
Octave Band Plots
A dedicated Octave Band () plot exists to plot frequency response, transfer functions, transmission loss, and insertion loss curves. The plot has several built in acoustics specific features like predefined weighting (Z, A, C, and user defined) as well as the possibility to plot the response in octaves, 1/3 octaves, or as a continuous response.
Figure 2-6: Sensitivity curve plotted as 1/3 octave bands and a continuous curve. From the Loudspeaker Driver model in the Application Library.
For details see Octave Band in the Results Analysis and Plots chapter in the COMSOL Multiphysics Reference Manual.
Absorptive Muffler: Application Library path Acoustics_Module/Automotive/absorptive_muffler
The Brüel & Kjær 4134 Condenser Microphone: Application Library path Acoustics_Module/Electroacoustic_Transducer/bk_4134_microphone.
Directivity Plots
Another acoustics specific plot, especially used for loudspeakers, is the dedicated Directivity () plot. The plot allows audio engineers to depict the spatial response of a loudspeaker as function of both frequency and spatial angle in a contour like plot. Representing the spatial response in this manner is a very common the loudspeaker industry. Measured data is often also represented in the same manner. The plot includes many options to format the plot to achieve maximal insight into the modeled data, for example, easy switch of the x- and y-axis (frequency and polar angle axis) as well as options to normalize the data with respect to a given angle or the maximal value.
Figure 2-7: Example of the directivity plot from the Lumped Loudspeaker driver model in the Application Library
For details see Directivity in the Results Analysis and Plots chapter in the COMSOL Multiphysics Reference Manual.
Lumped Loudspeaker Driver. Application Library path:
Acoustics_Module/Electroacoustic_Transducer/lumped_loudspeaker_driver