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Etude du logiciel CATT Acoustic Audience area mapping |
La boîte de dialogue Audience area mapping contrôle les paramètres de calcul et d'édition des résultats du module de calcul de cartographie.
Number of rays to use for coverage mapping. At least 10000 rays must be used for reasonable mapping. In general, the smaller the Map step the higher the number of rays has to be. With low ray-numbers the results will be too random to be useful. See also Auto number.
Automatic selection of a good/sufficient number of rays. This number is dependent on the room size, the map step and some other parameters. 1) One number is calculated to give one direct ray / m2 at a time corresponding to 80 ms arrival relative the direct sound for all positions. This give a good sampling of parameters such as D-50, C-80 and LF. 2) One number is calculated corresponding to one direct ray / 4 m2 at the longest hall dimension. 3) One number is calculated corresponding to one ray / map point at 80 ms relative arrival time. The highest of 1), 2) and 3) is selected. 2) will only be higher for rooms that are very big so that there is some chance to get back some detailed reflections from far-away surfaces and 3) will only be higher for very dense maps.
Truncation time in ms for rays to be traced. The time should correspond to at least 50% of the reverberation time (measures such as D-50 etc. are not much affected by the energy 30 dB down from the direct sound). See also Auto time.
Automatic selection of sufficiently long truncation time based on the estimated classical RT (only possible if rooms are closed and if classical RT does not differ too much from the actual one e.g. because of double-sloped decays).
Which audience planes to map. If audience planes that overlap in the z-direction are selected, only the highest located plane is used. In such a case it is better to run twice, once for the lower audience area and once for the higher. The selected audience planes will be marked gray in the VIEW4.PLT plot-file. Note: if planes that do not exist in the model are selected, it will not be trapped until the mapping actually is run.
The map is divided into a rectangular grid where the square grid step can be selected. If some part of a grid point, and thereby a fraction of the receiver sphere, should come outside the room (very close to a wall e.g.) the received energy will be too low. Similarly, if boxes are placed inside the room it may, for a big Map step, look like there are hits inside the boxes. Recommended step is 0.5 - 1 m.
The map points (center of the receiver spheres) are placed at the selected height above the selected Audience planes. The height should be half a Map step above the audience planes for normal audience area mapping but for special cases they can be placed higher (e.g. factory noise mapping where the floor can be set as the "audience" plane and the height to e.g. 1.8 m). To prevent receiver spheres to go down through the audience planes the lowest allowed height is checked to be = half a map step.
With this option selected direct sounds from each of the sound sources are allowed to interfere (two equal in-phase source contributions give close to +6dB while out-of-phase signals can be -10 dB down or more over an octave-band). Without this option the direct sound is, just like higher order reflections, added on a power basis (two equal source contributions always give +3dB). The interference calculation is based on digital octave-band filters and not only on the octave-band center frequencies (i.e. the interference is calculated with full bandwidth but the result is filtered in octave-bands so interference patterns will be somewhat smoothed). Note: the addition with phase affects LFC values too since a figure-of- 8 microphone is simulated for the lateral sound taking into account the reversed phase of reflections registered at the left side of the microphone (this is of little importance since LFC is not defined for use with multiple sources).
If only a combination of SPLdir, SPLcont, Closest and/or Delay and Direct only for mapping in time intervals are chosen, no ray-tracing needs to be performed so it is faster and high density maps can be used. This button sets these options in one step.
The mapping is performed only for the octave-bands selected unless sum is included. For RASTI mapping both 500 and 2k or sum have to be selected. For STIuser mapping all bands included have to be selected (see Preferences). To get a plot for the sum all bands will have to be calculated even if no plots are requested for them so that it takes longer to calculate e.g. 1k and sum (calculates for 125, 250, 500, 1k, 2k, 4k, 8k, 16k unless a Preferences option excludes 8k and 16k from the sum) than e.g. 1k and 2k (calculates only 1k and 2k). Also note that the Lp1m values affect D-50, C-80, Ts, etc. for sum while for single-source single-octave maps it has no effect other than for SPL (this is not a limitation it is just how the measures work – they are early/late sound ratios). If sum is selected all parameters can optionally be presented A-weighted instead of linear. This affects all measures for the sum so that e.g. D-50 will be the A-weighted D-50 and thus having the highest weight for 1k and 2k.
Since mapping does not generate any text result-files except mapping statistics, at least one of these plot options has to be selected.
Which directivity contours to include in the SPLcont plot. For details on directivity contours, see Section 4.3.
Mapping of RASTI with and without background noise (from General settings). The plot-file created, RASTI.PLT, shows 2D and 3D maps with and without background noise taken into account. Requires both 500 and 2k octave-bands or sum to be selected.
Mapping of STIuser with and without background noise (from General settings). The plotfile created, STIUSER.PLT, shows 2D and 3D maps with and without background noise taken into account. STIuser bands and weights can be selected in Preferences.
Option to include source id:s in map plots (useful to switch off if many sources are used not to clutter the view).
For each one of these three optional plot-files the information as well as its location on the
plot can be selected (upper left/right or lower left/right):
None no plot created for the position;
,2D a 2D map is created;
,3D a 3D map is created using a static parallel projection (same as for VIEW4.PLT);
SPLdir direct sound. Note that with more than one source the relative time delays are not
seen in this plot.
SPLcont direct sound -3, -6 and or -9 dB contours are plotted on the audience planes (see
Contours group). Note that with more than one source the relative time delays are
not seen in this plot. For details on directivity contours, see Section 4.3.
Closest means that the letter of the source group with the shortest delay is displayed
(electrical delays taken into account). To use this function with separate sources
use source numbers A0, B0, C0 instead of A0, A1, A2 etc. Can be used together
with Delay to optimize source delays.
Delay means that the shortest source delay is displayed (electrical delays taken into
account) and is only meaningful if more than one source is used. Can be used
together with Closest to optimize source delays.
RT’ means a reverberation-time measure that relates well to EDT and is derived from Ts (Temps central) assuming an exponential decay (RT' = 13.8 Ts), see Theory.
If None is selected for all four positions the plot-file is not created. If only a combination of
SPLdir, SPLcont, Closest, Delay and SPL|LF in time-windows (with Direct only) is chosen, no
ray-tracing needs to be performed so it is faster and high density maps can be used for
direct sound coverage tests. Note the shortcut button for direct sound only calculations
(Select direct….)
Auto spans the color palette as much as possible but fixed settings may sometimes be preferred so that comparisons between two calculation cases can be made. If the actual max/min values encountered are higher/lower than a selected fixed range, the max/min markers are drawn slightly above/below the color scale to indicate saturation. Note: the scale and the color palette can be changed in the View module.
Early sound coverage mapping can be selected in four different, possibly overlapping, timewindows. In the created plot-file view, the results for each time-window is placed corresponding to the time-limits in the dialog. Note: Times are relative arrival of the direct sound. If, for example, map number one is set to 0 to 0.1 ms, the direct sound coverage and the effects of source directivity and aim can be studied.
Mapping of sound pressure level (creates SPL_oct.PLT) in each selected time interval. The Scales settings for SPL affects the display scale. Tip: to map the direct sound set one of the time interval to 0 - 0.1 ms.
Mapping of LF (creates LF_oct.PLT) in each time interval (i.e. the fraction of lateral to total incidence). For the lateral fraction the head-direction used is according to head-direction chosen in General settings.
Maps only the direct sound from each source. The map titles will show SPLdir and LFdir instead of SPL and LF if this option is on.