Differents values with same parameters

[leofuy]

Hi,
Im running isimpa with same parameters but it give me differentes values fot RT15 when i run it several times. Even there are some high values in the second column.
What do you think it could be happening?

RT-15 (s)	RT-15 (s)	RT-15 (s)
1,53	1,46	1,48
1,54	1,41	1,36
0,84	0,61	0,86
0,38	3,92	0,64
0,87	0,65	0,65
0,88	2,69	0,95
1,06	2,34	1,05
1,01	1,79	0,99

Thanks for your time
Leonardo

[nicolas-f]

Hi,

SPPS is based on random emission of particles, so if you not have enough particle for your simulation you have varying result for each different random seed.

[leofuy]

Hi nicolás,
Thanks for your answer.
Is there some kind of formule that relate the number of particles and the volume of the model?
Leonardo

[nicolas-f]

No. But it is easy to spot it when you visualize the sound level of a receiver over time. Noise level should become more and more diffuse over time, but if you do not have enough particle you will see positive and negative peaks after some simulation time.

[leofuy]

This is what you talk about?
I have 250.000 particles.
The volume is 1316.
This is the sound level in one point:

	5.0 ms	10.0 ms	15.0 ms	20.0 ms	25.0 ms	30.0 ms	35.0 ms	40.0 ms	45.0 ms	50.0 ms	55.0 ms	60.0 ms	65.0 ms	70.0 ms	75.0 ms	80.0 ms	85.0 ms	90.0 ms	95.0 ms	100.0 ms
50 Hz	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	75.1	87.1	91.3	93.1	93.9	92.4	91.4	90.7	91.3	90.7	89.6	89.0
63 Hz	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	75.0	86.5	90.8	91.9	93.6	92.3	91.3	90.6	91.6	90.4	89.2	88.9
125 Hz	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	77.0	88.0	89.5	92.9	93.7	91.6	91.5	89.2	91.5	91.3	89.2	89.9
250 Hz	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	74.3	87.7	89.1	91.3	92.6	89.5	89.0	88.0	88.6	88.4	86.5	86.1
500 Hz	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	76.3	88.0	90.4	89.5	91.1	86.3	85.9	83.7	86.1	85.1	78.6	80.4
1000 Hz	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	77.0	86.8	89.5	88.3	89.3	83.4	85.2	82.4	84.7	83.3	63.4	73.7
2000 Hz	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	74.2	86.0	89.6	89.0	89.7	82.6	85.2	81.3	84.4	84.5	-inf	-inf
4000 Hz	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	75.3	87.2	89.1	89.3	88.7	83.4	85.6	82.8	85.1	81.8	-inf	70.3
8000 Hz	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	77.8	85.7	88.3	87.1	86.1	82.7	83.1	81.6	81.1	79.3	-inf	65.5
Global	-inf	-inf	-inf	-inf	-inf	-inf	-inf	-inf	85.5	96.6	99.4	100.3	101.2	98.5	98.2	96.7	98.0	97.3	94.9	94.9

fachada.csv

[nicolas-f]

Yes you see jittering is starting as soon as 660ms here

You should use "energetic" for spps method and see the result, increasing particle number if it is still jittering

[leofuy]

Estimado Nicolás,
Here i attach a new file.
It still have some errors with 850.000 particles and this config:

[nicolas-f]

Hi.

For RT-15 you only need 20 dB attenuation from the peak (-5 dB -> -20 dB):

https://i-simpa-wiki.readthedocs.io/fr/latest/room_acoustics_parameters.html#reverberation-time-t

"Limit value" is a parameter that will destroy sound particle after some attenuation is reached. Here it will destroy particle that lost more than 50 dB.