OS-E: 0320 Acoustic Analysis of a 2.1 Speaker using Infinite Elements

Demonstrate Infinite Elements, which is effectively modeled to measure the sound pressure of the 2.1 Home Theater System in OptiStruct with effective modeling practice.

Figure 1. FE Model with Infinite element, Sound source, Acoustic elements and Receiver. Model A

Model Files

Before you begin, copy the file(s) used in this example to your working directory.

Model Description

This example has a source plate (green in color) inside the speaker which is vibrating (unit displacement is applied as excitation) along the z-axis. The Source plates are then covered with acoustic fluid elements (front, back and top) as seen in Figure 1. Then the infinite elements are the skin of the front fluid elements whose normal must be pointing towards the receiver as shown, each speaker with IE will have their own pole (which is the center of the source) location. For pressure (as calculated on grids) contour, the receiver elements are configured with PLOTEL elements with fluid grids since you will be capturing the sound pressure on these elements. A direct frequency response analysis is run.

The FE Model properties are:
First order Solid elements
First order Shell
Infinite Elements
First order Shell
First order Shell
The MAT1 material properties are:
Young's Modulus
70000 MPa
Poisson's Ratio
Initial Density
2700 Kg/m3
The MAT10 material properties are:
Speed of Sound
343 m/s
Mass Density
1.21 Kg/m3


Figure 2 shows the pressure contour (Magnitude with phase) on the receiver and the vector plot of displacement of the source.
Figure 2. Displacement plots

Figure 3 shows the pressure contour (Magnitude) on the receiver and the vector plot of displacement of the source.
Figure 3. Pressure plots

As you observer from the contour plot, the acoustic pressure is concentrated in the center along with the imprint of the left and right speaker, hence this does not capture the interaction of the 3 source speaker correctly due to incorrect modeling.

For better modeling practice you will remodel the acoustic domain and the infinite elements, as shown in Figure 4. Model B (with one acoustic domain, 3-Infinite elements components with 3 same pole points), and Model C (with one acoustic domain, 1-Infinite elements component with 1 pole points) for comparison study.
Figure 4. FEM Model (Model B and Model C)

As expected, the Model B and Model C yield good and similar results.
Figure 5. Results Pressure Contour Comparing all 3 Models

Figure 6. Variation of Pressure (db20) over Frequency for all 3 Models

Note: Good model practice is recommended (as Model B and Model C) to obtain better results with infinite elements.