Using SPPS within I-Simpa

SPPS is already embedded in I-Simpa. Follow the next instructions to run a calculation with the SPPS code in I-Simpa.

Double left click on the TCR calculation code in I-Simpa to display all calculation paramaters:

• Frequency bands for the selection of the frequency band to be used for the calculation

• Meshing for the meshing configuration

• SPPS Calculation parameters for the calculation parameters

Right click on the selected calculation code to display all possible actions:

• Run calculation

• Job list

Frequency bands

This allows to define the frequency band that will be used for the calculation. This can be done:

• by hand, by checking/unchecking the frequency to be considered;

• automatically (“Automatic selection”), by using the contextual menu on the element “Frequency band” of the chossen code:

  • “Unselect all”

    Uncheck all frequency bands.

  • “Select all”

    Check all frequency bands.

  • “Octave”

    Check third ocave bands that are centred on the corresponding octave bands.

    • “All”

      All octave bands on the whole frequency range

    • “Building/Road”

      All octave bands between 125Hz and 4000Hz.

  • “Third octaves”

    Check the third octave bands, considering.

    • “All”

      All thrid octave bands on the whole frequency range.

    • “Building/Road”

      All octave bands between 100Hz and 5000Hz.

Meshing

Some calculation codes may require a meshing of the domain (SPPS for example). I-Simpa used the TetGen meshing code (A Quality Tetrahedral Mesh Generator and a 3D Delaunay Triangulator). See the documentation for more information.

Within I-Simpa, TetGen can be paramatrized:

• “Test mesh topology”

  Check/uncheck for activate the debug mode of TetGen (debug mode).

  Avertissement

  With the debug mode, the meshing is not realized.

• “Additional parameters”

  Add parameters to the TetGen default parameters.

• “Radius/Edge ratio”

  Defines the ratio between the radius of the sphere that would contain a mesh and the lenght of the mesh. This parameter could be useful in order to avoid long meshes.

• “Scene correction before meshing”

  Check/uncheck for trying to repair the 3D scene if possible.

• “User-defined paramters”

  Defines new parameters by replacing default parameters.

• “Surface receiver constraint”.

  Check/uncheck for using a given value of the mesh surface “Surface receiver constraint (m²)”.

• “Surface receiver constraint (m²)”

  Maximun accepted value of the mesh surface (m²) for a surface receiver. The value can be modified only if the “Surface receiver constraint” parameter is checked.

• “Volume constraint”

  Check/uncheck for using a given maximum value of the mesh volume “Volume constraint (m3)”.

• “Volume constraint (m3)”

  Maximun accepted value of a mesh volume (m3). The value can be modified only if the “Volume constraint” parameter is checked.

SPPS Calculation parameters

• “Active calculation of atmospheric absorption”

  Enables calculation of atmospheric absorption.

• “Active calculation of diffusion by fitting objects”

  Enables calculation of calculation of diffusion by fitting objects.

  Important

  If fitting zones are enabled, by checking this option, it disables the calculation of all fitting zones. If you uncheck this option, the individual configuration of each fitting zone is preserved.

• “Active calculation of direct field only”

  Enables calculation of direct field only. There is no calculation of the reverberant field.

  Astuce

  This can be useful if you want to realize a first calculation, as a reference, of the direct field at receivers. The second calculation (direct and reverberant fields) can thus be calculated and compared to the direct field (first calculation).

• “Active calculation transmission”

  Enables calculation of transmission through walls.

• “Calculation method”

  Selects the calculation method.

  • “Random”

    Select the Random method.

  • “Energetic”

    Select the Energetic method.

• “Echogram per source”

  Check to calculation an echogram for each sound source, for a given receiver. If uncheck, a global echogram is calculated by summing all source contributions.

• “Export surface receivers for each frequency band”

  Check to export the surface receiver results, for each frequency band. If uncheck, only the global value is exported.

• “Limit value of the particle extinction: ratio 10^n”

  For the “Energetic” mode only. It defines a limit value of the particle energy. If the decrease of the particle energy is less than this value (i.e. the particle energy is very low), the particle is removed from the domain. For example, if n=60, it means that all particles whose energy will decreases to 60dB, will be removed.

• “Number of sound particles per source”

  Defines the number of sound particles that are generated by the source.

  Avertissement

  The computational time depends on the number of particles. If you increase the total number of particles, you drastically increase the computaional time.

• “Number of sound particles per source (display)”

  Defines the number of particles that are used for the particle animation.

  Note

  Most of time, you need to consider only few hundreds or thousands particles for the animation. Incerasing this number, will decrease the memory resources.

• “Random initialization number”

  Initialize the random number series. If you select a number that is different from “0”, the random number series will always be the same. The starting number of the random number series will depend on the number you will consider for this parameter.

  Avertissement

  In a multithread simulation, I-Simpa/SPPS can not control the generation of random numbers. It means that this paremeter will have no effect. Multithread simulation occurs when several frequency bands are considered in the simulation. To avoid multithreading, consider only one frequency band calculation.

• “Receiver radius (m)”

  Defines the receiver radius (in m).

• “Simulation length (s)”

  Defines the duration (in s) of the simulation.

• “Surface receiver export”

  Select the kind of results that is exported.

  • “Soundmap: intensity”

    Intensity level (in dB).

  • “Soundmap: SPL”

    Sound pressure level (in dB).

• “Time step (s)”

  Time step (in s) for the calculation.

Computational time optimization

The computationnal time depends mainly of the Number of sound particles per source. Thus, in the SPPS code, each sound particle is followed, at each “Time step” during its propagation inside the 3D domain, experiencing absorption, reflection, diffusion… and so on, during the “Simulation length” and/or untill the particles disapears when its energy is to small.

Considering a small number of sound particles may not produced relevant results to proceed an interesting acouctic analazis of the 3D model. Thus, it is necessary to consider a large number of sound particles. Assigning the good value for large is difficult and depends mainly on the scene size and the absorbent nature of the scene (surface absorption and volume absorption).

Few recommandations to evaluate the computationnal time:

• the number of sound particles defined in SPPS (“Number of sound particles per source” parameter) is defined for each sound source. Considering N sound particles per source and M sound sources will generate N x M sound particles in the domain;

• one calculation is done for each frequency band: considering F frequency bands will be equivalent to a calculation with F x N sound particles for one source (or F x N x M for M sources). Note that, by default, the computation is paralleleized on the processor core, for each frequency band (a frequency band for a given core). So the increase of computional time with the nimber of frequency band is not linear;

• in the “Energetic” mode, each sound particle is “alive” during its propagation untill its energy is below a ratio of the initial energy (see “‘”Limit value of the particle extinction: ratio 10^n” parameter). Increasing n will keep the sound particles longer in the domain, which increases the computational time;

• in the “Random” mode, each physical phenomena (absorption, diffusion) is applied by considering probabilistic approaches. Using this mode, the computational time is drastically decreased, but the quality of the results is aslo decrease. It is suggested to consider the “Random” mode at the initial step of the study, and then to change to the “Energetic” mode in order to obtain the final result.

SPPS Results

All the results are displayed in the Results tab, following a specific Tree structure. The content of the tree structure depends of the elements defined in the Scene tab, and of additionnal processes execute on the result files (such as for creating room acoustics parameters).

Comments:

• All folders and files in the tree results can be renamed. A default name is created at the end of the calculation process.

• Some folders may be repeated several times (for example, as many times as (AMTA) there are Punctual receivers)

Tree structure

❙— 📁 SPPS [Root folder]

❙— 📁 Date_folder [folder; AMTA Calculations]

❙— 📁 Intensity animation [folder]

❙— 📁 Frequency folder [folder; AMTA Frequencies]

❙— 📄 Intensity [file]

❙— 📁 Punctual receivers [folder]

❙— 📁 Punctual receiver name [folder; AMTA Punctual receivers]

❙— 📄 Advanced sound level [file]

❙— 📄 Punctual receiver intensity [file]

❙— 📄 Acoustics parameters [file; see]

❙— 📄 Advanced acoustics parameters [file]

❙— 📄 Schroeder curves [file]

❙— 📄 Sound level [file]

❙— 📄 Sound level per source [file]

❙— 📁 Surface receivers [folder]

❙— 📁 Frequency [folder; AMTA Frequencies]

❙— 📄 Sound level [file]

❙— 📁 Global [folder]

❙— 📄 Sound level [file]

❙— 📄 SPPS particle statistics [file]

❙— 📄 Total energy [file]

❙— 📄 config [file]

❙— 📄 projet_config [file]

Intensity

Advanced sound level

In addition to classical room Acoustics parameters, some Advanced acoustics parameters can also be calculated. The calculation of this advanced room acoustics parameters needs specific calculation of sound levels at a punctual receiver.

This Advanced sound level .gap file display the temporal evolution of the impulse response, for each frequency band, as a data table, weihgted by \(\cos \theta\) (LFC and LG) and \(\cos^2 \theta\) (LF and LG).

Punctual receiver intensity

Acoustics parameters

Given the nature of the Sound level .recp file (i.e. an echogram), the contextual menu that is associated to this Sound level .recp file allows to calculate several room acoustic parameters:

• Sound Pressure Level (SPL) in dB

• Sound Pressure Level (SPL) in dB(A)

• Clarity C (in dB)

• Definition D (in %)

• Central Time Ts (in ms)

• Reverberation time RT (in s)

• Early decay time EDT (in s)

• Stage Support ST (in dB)

Several parameters can be given by the user in order to calculate user-values of some room acoustics parameters:

• Clarity: fix the value of the temporal limit of integration, usually 50 ms

• Definition: fix the value of the temporal limit of integration, usually 50 ms

• Reverberation time: fix the value of the sound level limit of integration, usually 30dB

Astuce

Multiple calculations are allowed for each paremeter, by using the semicolon “;” between parameters.

After the calculation parameters, two files are created in the corresponding folder:

• “Acoustic parameters”

  This file provides access to the room acoustics parameters in the form of a data table.

  • The parameters are given for each frequency band of interest.

  • When allowed, the Global value (i.e. the sum of all frequency bands) is calculated and displayed at the bottom of each column.

  • When allowed, the Average value (i.e. the mean value on all frequency bands) is calculated and displayed at the bottom of each column.

Advanced acoustics parameters

In addition to classical room Acoustics parameters, some advanced parameters are also calculated, and displayed in the Advanced sound level file.

The contextual menu that is associated to sound level” file allows to calculate several room acoustic parameters:

• Early lateral energy fraction LFC (in %)

• Early lateral energy fraction LF (in %)

• Early lateral energy LF (in dB)

• Strength G (in dB)

Data display:

• The Global value (i.e. the sum of all frequency bands) is calculated and displayed at the bottom of each column.

• The Total value (i.e. the sum of all time step) is calculated and displayed at the end of each row.

Several parameters can be given by the user in order to calculate user-values of advanced parameters:

• LF: fix the value of the temporal limit of integration, usually 80 ms

• LFC: fix the value of the temporal limit of integration, usually 80 ms

Astuce

Multiple calculations are allowed for each paremeter, by using the semicolon “;” between parameters.

Schroeder curves

It displays the temporal evolution of the Schroeder’s curves [Sch65], for each frequency band, as a data table.

Astuce

User can create charts for representing data from the data table. See charts creation

Sound level (punctual receier)

Double left click on a Sound level .recp file open a new winodw with three tabs

• “Sound Level SPL (dB)” tab

  It contains the temporal evolution of the quantity, for each frequency band, as a data table.

  • This tab is opened by default.

  • The values are represented in sound pressure levels (SPL).

  • The Global value (i.e. the sum of all frequency bands) is calculated and displayed at the bottom of each column.

  • The Total value (i.e. the sum of all time step) is calculated and displayed at the end of each row.

• “Sound Level SPL (dB)” tab

  It provides a graphic display of the Global value.

  • The temporal evolution of the Global value is displayed, as an echogram.

  • The cumulative quantity of the Global value is displayed, according to the Schroeder’s backward integration [Sch65].

• “Spectrum” tab

  It displays a spectrum at the punctual receiver.

Double right click on a Sound level .recp file open a contextual menu that allows to calculate Acoustics parameters.

Sound level per source

This file contains the sound level and the spectrum per sound source. Double left click on a .recps file open a new winodw with two tabs:

• “Sound Level per source, SPL (dB)” tab

  It contains the sound level per source and f each frequency band, as a data table.

  • This tab is opened by default.

  • The values are represented in sound pressure levels (SPL).

  • The Global value (i.e. the sum of all frequency bands) is calculated and displayed at the bottom of each column.

  • The Total value (i.e. the sum of all time step) is calculated and displayed at the end of each row.

• “Spectrum” tab

  It provides a graphic display of the spectrum contribution for each sound source.

Sound level (surface receiver)

A Surface sound level .csbin file contains the temporal evolution of a quantity that represents an acoustic intensity on a surface.

Depending of the calculation parameters, one can obtain, for each surface receiver, by default, on Global value (in the “Global” folder) and, in addition, the result for each frequency band in a corresponding folder.

A right click on a surface receiver file opens the contextual menu, with specific actions:

• “Acoustic parameters”

  Allows to compute relevant room acoustics parameters on the surface. Depending of the selection, it creates additional files within the corresponding folder.

  • Clarity C (in dB)

  • Definition D (in %)

  • Central Time Ts (in ms)

  • Reverberation time RT (in s)

  • Early decay time EDT (in s)

  • Stage Support ST (in dB)

• “Load animation”

  It allows to represent the spatial variation of the indicators that is selected. If the indicators contains some time dependent value, it can displayed an animation. On can interact on the animation with the “Simulation” toolbar.

  • “Instantaneous value”

    Show the value of the given indicator at each time step.

  • “Cumulative instantaneous value”

    Show the value of the given indicator at each time step, by cumulating all past steps.

  • “Total value”

    Show the total value of the given indicator. No animation.