COMSOL 6.2 - Impulse Response

) to a 1D plot group to create an impulse response plot. After defining the characteristics of the impulse response, click (

) to create the impulse response plot. Add a Color Expression or Energy Decay subnode as needed. The impulse response plot reconstructs the impulse response based on a Ray Acoustics simulation.

	For details on setting up a Ray Acoustics model and postprocess the impulse response, see Impulse Response and Receiver in the Acoustics Module User’s Guide.

	Go to Common Results Node Settings for links to information about these sections: Title and Coloring and Style.

From the list, choose (the default) or .

If you chose , from the list, choose an applicable dataset or . The default option, , uses the dataset from the parent plot group node. Only the Receiver 2D and Receiver 3D datasets are valid for this specialized plot.

If you chose , choose an applicable functions or from the list. Click the button to update the list of functions.

From the list, choose an interpretation of the frequency: (the default), , or . This selections should coincide with the frequency interpretation used in boundary conditions and sources in the underlying Ray Acoustics simulation. The frequency content and resolution of the impulse response are based on this selection.

Set up the variables that are necessary for reconstructing the impulse response. In practice these variables are used to define and add the contribution of each ray that intersects the receiver dataset to the impulse response.

For all text fields, click the (

) button to select a predefined quantity and replace the entire contents of the field.

From the list, choose a transformation of the data on the x-axis: (the default) for no transformation, or . If you select to display a discrete Fourier transform (DFT), choose one of the following options from the list:

If you have selected or , you can select the check box to present the values in dB. From the list, choose (the default) or . The display in dB requires a reference value. From the dB reference list, choose (the default) to use the maximum value as the reference, or choose to enter a suitable reference value in the field.

If you have selected , , , or , the following additional settings are available: To specify this value manually, select the check box and enter a value in the associated field. If desired, select the check box to use an inverse DFT. Select the check box to set the DC value (zero frequency component) to zero (not available if is selected). The check box is selected by default to not include the last sample in the transform (not available if is selected). The and check boxes are selected by default. Clear one or more of these check boxes if you want to exclude those steps.

In this section, only available if you have selected from the list above, you can add a moving average when analyzing an impulse response plot in ray acoustics. To do so, select the check box. You can then choose (the default) or from the list to choose the type of moving average. For the latter option, also specify as a positive integer (default value: 1).

The following settings are available to control the filter kernel used when reconstructing the impulse response. Each ray contributes with a power, arrival time, and frequency content to the time-domain signal.

If you have selected a dataset, use the following settings:

Select to (not selected per default). This options removes the unphysical parts of the impulse response signal that appear before the arrival time of the first ray. This part is generated due to the nature of the window functions used for the signal reconstruction.

Select (not selected per default) to switch the impulse response generation to the legacy method where a random phase is applied to all rays. In contrast, the default method bases the phase on the number of reflections. The default method leads to consistent values for the direct sound.

The following settings are available with all sources:

From the list, choose what to show: (the default), or . Choose to see the signal of each band separately and how they are separated in frequency.

Select the as either the (the default) or .

For the first option, enter the ripple factor δ (SI unit: Hz). The default is 0.05.

For , if desired, enter an expression of the kernel itself in the time domain in the

field. For an FIR filter it is usually a filter (by default, ) multiplied by a window function (by default, ). These default factors are defined in the table below. Also, if desired, enter expressions for the kernel expression using the definitions in the table. The default parameters set up the Brick-wall with Kaiser window filter.

The check box is selected by default to display the plotted expressions to the right of the plot. In plots where each line represents a certain time value, eigenvalue, or parameter value, these values are also displayed.

When is selected from the list (the default), select or clear the and check boxes to control what to include in the automatic legends (by default it includes the solution only). You can also add a prefix or a suffix to the automatic legend text in the and fields. If is selected from the list, enter your own legend text into the table. If is selected, you can use the eval function to create an evaluated legend text in the field that include evaluated global expressions such as global parameters used in sweeps. For the numerical evaluation, you can control the precision in the field (default: 3).