This article provides detailed instructions on how to make sound decisions about settings in the main Pachyderm Interface.

Running an Image Source Simulation (Specular Only)

It is important, when performing an image source simulation, to understand that a room can never be accurately understood by only simulating the specular component of sound propagation. In such a simulation, the impulse response is entirely unsuitable for things like parameter analysis or auralization. Still, there are times when it may be desirable to run a simulation without having to worry about the time required to obtain the diffuse component.

In order to run a specular only simulation, check the box next to Image Source Solution and uncheck the boxRaytracing Solution. Then select the number of reflections to calculate for by setting the order at the numeric control next to 'Reflection Order.'

A note on selecting the order of reflection: the amount of time it takes to run the image source method is exponentially (!!!) proportional to the number of orders chosen for the simulation. So it is not recommended that for a typical model, anyone try to run more than 2 or 3 orders of image source (though it is possible).

If higher orders are desired, there is another option which can be added to the image source method, which is Image Source Tracing This method uses a simple raytracer to search the model for potential specular reflections up to whatever cutoff time you choose. The act of using a raytracer to find specular reflections is less deterministic than doing an image source calculation, and so it is unlikely that using this tool will find all specular reflections which exist within the cutoff time set. The advantage is that using a raytracer also dramatically reduces the number of wall combination checks which are searched for specular reflections. Running this method, I have occasionally found reflections of orders greater than 100.

When the 'Image Source Tracing' option is checked, the 'RayTracing Solution' option is disabled, as the two are written in such a way that they can not be combined with accurate results.

Article on Theory coming soon...

A 52nd order specular reflection.

Running a Raytracing only Simulation (Specular and Diffuse)

This simulation method can be used for parametric analysis and auralization. It can be less accurate than a simulation with Image Source and Raytracing combined.

In order to run this method, uncheck the Image Source Solution option, and the Image Source Tracing option, and check the Raytracing Solution option. Then set the Number of Rays and the Cut Off Time.

It is still unclear what settings for the Number of Rays are needed. For the time being, we recommend between 25 and 50 rays per cubic meter of volume in the room.

We recommend that Cut Off Time be set to between 75% and 100% of the longest expected Reverberation Time (T-30) of the room. Getting this right may in some cases require some trial and error by the user.

Article on Theory coming soon...

 

Running a Combination Image Source and Raytracing Simulation (Specular and Diffuse)

The most accurately benchmarking method Pachyderm offers to date is the combination Image Source and Raytracing method. This type of simulation supplements the very thorough, but sometimes incomplete results of the Raytracing method with the deterministic results of the Image Source method for the early part of the impulse response.

In order to run a combination simulation, check the Image Source Solution option and the Raytracing Solution option. (you may have to uncheck the Image Source Tracing option in order to enable Raytracing Solution. Similarly, you may notice that when you check the Raytracing Solution option, Image Source Tracing is disabled. This is because these two methods can not be combined with accurate results in Pachyderm).

Then set the Reflection Order, the Number of Rays and the Cut Off Time. Again, we recommend:

  • The Reflection Order be set no higher than 2 or 3 orders, but the higher the better.
  • The Number of Rays be set to between 25 and 50 rays per cubic meter of room volume.
  • The Cut Off Time be set to a minimum of 75% of the expected Reverberation Time (T-30) of the room.

If you have any questions, please feel free to contact the author.