Assigning Materials
When you have created a simulation the list of layers that were placed under Treble > Geometry in the SketchUp model will appear inside the Materials tab. Each layer can contain multiple surfaces. If a layer has more than one surface, it is indicated by a grey arrow to the left of the layer name. These layers and surfaces are where acoustic materials can be assigned.
At the bottom of the list of layers you can find the reverberation time estimates (T60 [s]) that are computed using Sabine's formula once all layers have been assigned a material. The estimate can help you quickly dial in your designs, but to get accurate and reliable results you should run the full simulation.
Material library
To open the material library click on the material of a layer under the Material column (possibly the material is unassigned).
The material library will appear to the left of the list of layers. The library comprises around 450 different materials generated with the Treble material engine. Additionally, you have the option to create custom materials. For more information on materials in Treble, refer to the Materials section.
At the top of the material library you will find the filtering and searching functionality.
Material details
At the bottom of the material library, you can inspect the set of absorption coefficients for each material, as well as the default scattering and what category this material belongs to.
You can open the Material details by clicking the cogwheel in the upper right corner. There, you'll find the absorption coefficients for each octave band, ranging from 63 Hz to 8 KHz, along with the reflection coefficients.
Material details popup
Assigning a material to a layer
To assign a material to a layer, click on the layer you wish to assign a material to. Upon clicking, the layer is selected, and the corresponding surfaces in the 3D view will be highlighted in red. You can also select a layer by clicking on the surface in the 3D view.
When selecting a layer the corresponding surfaces in the 3D view is highlighted in red.
In the material library an Assign button will appear when hovering over a material. Click the Assign button to assign the relevant material to the selected layer. The material will then appear as selected. This will apply the selected material to all the surfaces in the layer.
For keyboard shortcuts, you may utilize the "Tab" key to navigate to the subsequent layer row, and "Ctrl" or "Command" + "Tab" to navigate to the previous layer row, while the "Up" and "Down" arrows can be employed to switch between different material rows. Once you have highlighted the desired material row, you can then use the "Enter" key to assign it to the selected layer.
Layer with multiple surfaces
If a layer consists of multiple surfaces, you can assign materials to each surface individually. Click on the small triangle on the left of each layer name to reveal the sub-surfaces. The triangle should now point downward, showing the sub-surfaces.
Click on the material of a surface to assign a specific material, just as you did for the layer. A layer with different materials for its surfaces will display - multiple - in the material column.
The Cabinet layer consists of multiple surfaces
Assigning a scattering coefficient
The scattering coefficient is used in Treble's geometrical acoustic solver only, where it determines how much acoustic energy is scattered for each reflection of the rays being traced around the room. For most geometrical acoustic solvers it is recommended to have a minimum scattering of 0.1 on most surfaces, this is to make sure that rays don't get trapped in specular reflections between parallel walls and to ensure a diffuse sound field so the principles of GA upholds. You can assign a scattering coefficient on a layer level or to each of its sub-surfaces. Each material has a default scattering value but this scattering value can however be freely edited for each surface within the layer as shown in the image below.
Note that if your settings are set to use both solvers, the scattering value will only be applied in the GA simulation. If using wave based solver, the scattering value will be unused, and any scattering will come from geometrical details.
Single value scattering
Click on the number in the SCATTER column, input the number of your choice from 0.00 to 1.00. It should be noted that the scattering coefficient input will only affect the simulation results of the geometrical acoustics solver, that is above the chosen transition frequency if running a hybrid simulation. The scattering effect in the wave based solver will solely depend on the geometrical details of the model in question. The scattering coefficient chosen will be mapped onto a frequency dependent curve shown in the following figure for a few inputs values of the scattering coefficient.
Read more about how the scattering coefficient is used in our technical reference here.
Scattering per octave band
If you want more control over the scattering value per octave band in the simulation you can click the :::: icon that pops up when you click the scattering value field. Here you can freely choose which scattering coefficient is used in each band in the GA simulation.
If you decide to go back to a single value input just click the single dot to switch back to a single value input.
Suggested values for scattering
The scattering coefficient for flat surfaces is usually somewhere between 0.05 and 0.10 and it represents the percentage of the rays that in the geometrical solver will deviate from the path reflected in a specular manner. For guidelines on scattering values see the following table.
| Materials | Scattering coefficient |
|---|---|
| Audience area | 0.6 - 0.7 |
| Rough surface | 0.4 - 0.5 |
| Filled bookcase / Furniture | 0.4 |
| Textured ceiling | 0.3 - 0.4 |
| Brick wall exposed | 0.1 - 0.2 |
| Smooth surface | 0.05 - 0.1 |
Video-guide
How to assign and create materials in Treble: