For some ray acoustics applications it can be advantageous to stop rays once their intensity falls below a certain threshold. This can be simply achieved at walls using the Primary ray condition with an Expression. Here you can enter a logical expression that must be satisfied for a ray to undergo a certain type of ray-wall interaction. For the intensity specify a condition of the type rac.I<threashold. Then the ray is either reflected according the selected condition or it can Freeze or Disappear, depending on your selection.

The number of reflections can be used in such an Expression. This variable is readily set up under the Additional Variables section.

The Ray Termination feature can also be used in a similar manner to remove rays for certain conditions, without the need for a wall interaction.