different results for the same data

[Vitor Rosão]

Good Morning

I made a new rectangular scene with 5x10x3 m. I defined all surfaces with absorption 0.2 except the ceiling that I put with 0.8. I placed a source in the coordinates (0.1, 0.1, 1.5) and a receiver in the coordinates (2.5, 5, 1.5). I performed the calculation and defined a decay of 20 dB (T20). Doing the calculation several times the results are different. For example, in 3 calculations I obtained the following values for 500 Hz, for the receiver in question: 0.71s; 1.07s; 0.84s. Is this difference normal? Any recommendations? Thanks

[JP]

Dear Vitor

If you use SPPS, you may have to use a number of particles that is sufficient for the modelling to converge to the 'good' values (so increase the number of sound particles in the SPPS calculation parameters). Indeed, I-Simpa uses random process to model the physical phenomena, such as emission, propagation, absorption... When you use very large absorption on surfaces, you may considered even more particles, sine many of them will be absorbed by the corresponding material. The number of sound particles in the model will decrease quickly. Instead of using the 'random' approach in SPPS (see SPPS configuration), you may use the 'energetic' approach instead. In this case, the number of sound particles will be keep constant in the model; only the energy of the sound particles will be modified at each collision.
See here for more information: https://i-simpa-wiki.readthedocs.io/fr/latest/code_configuration_SPPS.html#computational-time-optimization

Best regards.