The impulse response (IR) in a room acoustics simulation can be analyzed by collecting the ray information using the Receiver data set and then graphically postprocess using the Impulse Response plot. The IR can be determined for sources and boundary data (absorption coefficients, scattering parameters, source directivity, volume attenuation etc.) given in octave, 1/3 octave, or 1/6 octave bands.

Use a Receiver 2D () or Receiver 3D data set (), selected from the More 2D Data Sets submenu and the More 3D Data Sets submenu, respectively, to collect the data necessary to visualize the impulse using an Impulse Response Plot. The Impulse Response plot uses the data from a Receiver data set as input

Select the appropriate ray data set in the Data set list. Then select the frequency parameters that should be used by the receiver; select one frequency for a single band analysis or all for the broad band analysis. This is the typical behavior if a parametric sweep has been set up, as described in Preparing a Room Acoustics Simulation.

From the Directivity type list, choose Omnidirectional (the default) or User defined to enter a directivity expression in the Expression field (unit: dB).

Extra time steps are used get a more precise evaluation of the arrival times if the rays and the receiver data set. This is especially important if only a few times have been stored in the output. You can control the added extra time steps from the Maximum number of extra time steps rendered list. It is good practice to increase the value until you get a convergence. Use a Ray plot of, for example, the power rac.Q and then increase the extra times values until the solution no longer changes (is converged). This is exemplified in the Small Concert Hall Acoustics tutorial model.

From the Interpolation between time steps list, you can choose to use a Linear interpolation (the default) or a Cubic interpolation, which can be more exact but requires a larger computational effort.

Under Normal variables and Other variables, if desired, you can change the default names of the created variables for the normal directions (nx, ny, and, in 3D, nz) and for the Distance traveled by a ray inside the receiver, the Volume of the receiver, the Directivity, and the First ray arrival time.

The main purpose for the Receiver data set is to be used as input for the Impulse Response Plot. However, the data generated by the data set can also be exported and used in an external analysis tool or software.

Right-click the data set and select Add Data to Export, then enter the desired data. For example, export the arrival time of the rays t, the frequency of the rays rac.f, the power of the rays rac.Q, the distance traveled by the rays in receiver re1dist, and so forth. The exported data can be stored and sorted in several formats.

When working with phase alignment of loudspeakers, it can be useful to evaluate the arrival time if the first ray. This is easily done in a Derived Values > Global Evaluation feature that points to the receiver data set. Simply evaluate the special variable re1first.

In room acoustics applications, the impulse response (IR) of a source-receiver configuration represents one of the most important postprocessing results. To create the plot based on the data collected by the Receiver data set, add an Impulse Response subnode () to a 1D plot group to create the impulse response plot. After defining the characteristics of the impulse response, click Plot () to create the plot. For further analysis of the IR data, it is recommended to export the plot under the Export > Plot node and run the analysis in an external software. This could, for example, be to extract room acoustics metrics like the reverberation time and clarity, or use the IR for auralization.

In the ray tracing methodology it is, as discussed above, typical to characterize sources and boundaries in frequency bands. This also means that some of the frequency content is lost. This frequency content is reconstructed when determining or reconstructing the IR. For each ray that interacts with the receiver, a small piece of signal with appropriate amplitude, arrival time, phase, and frequency content is added to the IR. The sum of all the contributions reconstruct the full IR (see Ref. 20).

From the Data set list, choose the appropriate Receiver Data Set. Then from the Frequency interpretation list choose an interpretation of the frequency: Octave (the default), 1/3 octave, or 1/6 octave. This selections should coincide with the frequency interpretation used in boundary conditions and sources in the underlying Ray Acoustics simulation, as described in Preparing a Room Acoustics Simulation. The frequency content and resolution of the impulse response is based on this selection.

From the Transformation list, choose a transformation of the data on the x-axis: None (the default), for no transformation, to show the time domain signal, or Frequency spectrum. The latter will perform an FFT of the IR and depict the amplitude as function of frequency.

The following settings are available to control the Kaiser-Bessel window functions (see Ref. 21) that are used to reconstruct the frequency content of the impulse response. Each ray contributes with an amplitude, arrival time, and frequency content to the time domain signal.

Select to Remove noncausal signal (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.

You can also change the Coloring and Style of the graph or add and format a legend in the Legends section.

The energy response depicted as a reflectogram or ehogram can be plotted using a Ray (Plot) and depict the expression re1dist*rac.Q/re1vol. This will give the intensity received by the “microphone” for each ray.