AFMG Network Forum

Guillaume.M · Member

Hello,

I am trying to run a simulation with reverberation in an architectural ambitious train station. The acoustic model I did is quite simple (373 faces), but I have 60 speakers (3 different type). I would like to check the Direct SPL and STI-PA with a background noise of 60.
I have an error in the simuation : Error in RenderScene in line 24.

Someone can advice how to bypass this error to get the result of the simulation?

Thanks and regards,

Guillaume Massardier

AFMG Pedro Lima · Forum Moderator

Guillaume,

This error usually occurs whenever using too high resolution. In your case the number of speaker must be contributing also.

Have you tried restricting the number of speaker on per simulation? You can probably simulation sets of speakers depending on your model to examine áreas separetedly.

If I remember correctly, you tried to model the 60 dB noise floor by adding a number of speakers in order to create a line source. Is that right?

If that's the case, maybe it would be interesting considering this noise floor by means of the table with constant 1/3 octave noise values, instead of using the speakers. This should diminish considerably the calculation time.

If you want to, you can send me your model so that can take a closer look.

Hope this helps,
Pedro

Guillaume.M · Member

Hi Pedro,

Thanks for your prompt answer.

In fact, this one is another model. I just check the SPL distribution and the STI distribution on a plateforme with the existing equipment (So I cannot remove some speakers).

I am using a resolution of 0.5 with reverberation.

I send you an email with the model. Thanks and regards,

Guillaume

AFMG Pedro Lima · Forum Moderator

Guillaume,

What values for the RT are you using? Are you asking EASE to calculate them or you are using custom values?

Also, the STI calculations you are performing are based on Standard Mapping or AURA?

Pedro

AFMG Pedro Lima · Forum Moderator

Dear Guillaume,

I can see that there has been a considerable evolution with respect to the drawings since the last post you made. The ones you sent me seem already much better.

There still some issues to fix and observations to make, though:

Please check the Faces orientation. The yellow side is the reflective side (also the side that will use the Front Material). It seems there are a number of inverted Faces on you're drawing.

There are also some Two Fold Faces where there could be simple Faces. Some are also inverted.

There issues above are not important if you are performing Direct Sound calculation only. But:

If you would like to perform STI calculations you MUST have Faces being correctly used. Also, please notice that Eyring and Sabine formulae for the Reverberation Times do not apply for this train station model. Please refer to Eyring and Sabine for more information. That means you cannot estimate the STI by means of standard mapping (which uses information statistical for the RT based on that formulae). On should use ray-tracing based algorithms, such as the ray-tracing feature or AURA. In the later case you need to have a closed model (due to considerations for that algorithm). Although you have an open space, that should not be a problem. You can just close the model with 100% absorptive Faces where there are open spaces.

The errors you reported above are generated whenever you perform what type of calculation? Standard Mapping, AURA, Ray Tracing,...? What are the settings you use so that I can try to reproduce it?

Best Regards,
Pedro

hasia · Member

Hi,
You mentioned that "Eyring and Sabine formulae for the Reverberation Times do not apply for this train station model. Please mention a reference.

AFMG Pedro Lima · Forum Moderator

Dear Hasia,

Please let me provide you some overview of Mr. G. Massardier's model from 2013: it was the preliminary EASE model of a roughly 150 meters long by 30 meters wide train platform, with open sides, hard floor and relatively reflective - 6 meters high - ceiling with a considerably large opening through it's extension, providing access for a second floor.

Quite a few equations to calculate the Reverberation Time of a room have been elaborated by different authors, since the introduction of the term by Sabine. These, in general, consider different assumptions for the room geometry and the distribution of the materials inside, so that the RT could be calculated for different room forms. If the requirements for a given formula are not met, the results may not be adequate. Being one of the oldest formulas, you will find numerous references to Sabine equation and more information on it's premises. Among these references:

- Lawrence E. Kinsler, Austin R. Frey, Alan B. Coppens, James V. Sanders, Fundamentals of Acoustics
- Michael Vorländer, Auralization: Fundamentals of Acoustics, Modelling, Simulation, Algorithms and Acoustic Virtual Reality

The platform above mentioned in general won't have a sound field that is diffuse enough. You can for instance already notice from the open sides in this rectangular space that sound will be largely "absorbed" in the horizontal direction, while it will persist for some time in the vertical direction. Roughly speaking.

I hope this helps clarifying the thoughts of my previous comment.

Best Regards,
Pedro

hasia · Member

Thanks Pedro for the explanation.