Pachyderm Acoustic

185 members

Description

Pachyderm is a plugin largely used by Designers and Scientists alike to simulate acoustics in buildings, rooms, cities, and other settings.

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Simple Box Test

by rpict

Mar 3, 2023

While doing a simple TestBox test with Pachyderm against a Sabine excel calculation, I get discrepancies in reverbration time, I can't understand. I'm obvously to stupid or lack information.


Any insight would be appreciate.

See attached Rhino and Excel File.

  • up

    Arthur van der Harten

    Hello.

    No worries. We are all here to learn, hopefully.

    A fundamental property of the Sabine equation is that it assumes a diffuse field, so there will be many cases in which your Pachyderm simulation will differ with Sabine. The main reason for this is that Pachyderm will properly calculate strong, late, specular reflections that lead to things like flutter echoes. (Not all the tools out there will do that for you.) Flutter has the effect of severely lengthening reverberation, and is considered a defect in acoustic quality. If you raise the scattering to a higher number, you will find that Pachyderm's answer comes closer to the Sabine prediction.

    I cracked open your model, and noticed that scattering was not set for any of the materials. This is why your impulse response came out so spiky. You must set scattering - very important. Even flat materials scatter a little bit. There are buttons in the scattering controls that allow you to set good pre-sets for gypsum board and glass, and help you set scattering for articulated surfaces).

    Also, make sure that your calculation is set for a sufficiently long cut off time. If the Schroeder Integral (red line) is not linear for between 5 and 35 dB, then your calculation's simulated time frame was not long enough.

    Hopefully this helps.

    Arthur

    1

    Mar 3, 2023

    • up

      Arthur van der Harten

      Hi,
      I'm glad it is working better for you.
      Yes, the convergence algorithm is something I invented, and to be honest, I wasn't entirely certain where the threshold should be. Several years in, and having used it myself a number of times, I have some ideas to improve it, but for the most part, minimum conference l convergence is better than I thought it would be, and 'detailed' is as you say, not practical...

      So, feel free to use minimum convergence. If you happen to have a model that you think minimum convergence isn't always working for, then take note of how many rays minimum tends to use, and click 'specify' instead, and enter a higher number of rays yourself. I would suggest doubling or tripling.

      In a future version, I will hopefully have a better solution.

      Arthur

      Mar 8, 2023