Defines the required thickness in meters of material before sound drops to inaudible levels.

The sound.transmission texture property defines the required thickness in meters of material before sound drops to inaudible levels. This property is used by the audio module to determine the transmission loss for sound passing through material after applying absorption. The reflected sound energy is the remaining amount of sound energy after absorption and transmission. Hence if you want a fully reflective wall set transmission to 0.

The thickness of a material is defined as the distance between the model face where the sound enters the surface and the first model face it exits. Faces are classified using the orientation of their face normal compared to the sound travel direction:

• Entering faces: face normal points in the opposite direction
• Exiting faces: face normal points in the same direction

Another way to look at it would be saying “entering faces” point towards the sound wave while “exiting faces” point away from the sound wave.

The “exiting faces” are not required to be located in the same Component resource. Actually in most of the situations this is not the case.

If no “exiting face” exists the thickness is considered to be infinite and sound waves are inaudible.

The property value is of single value type and has to be 0 or larger. With a value of 0 sound passing through the material is always inaudible. For larger values the sound volume drops linear with distance travelled in the material.

The “sound.transmission.lower” and “sound.transmission.upper” properties are multipliers for this property for different frequency ranges.

The default value is 0.4 which equals a 40cm thick brickwork wall plastered on both sides.

Typical values:

• Brickwork plastered both sides: 0.4
• Brickwork plastered one side: 0.92
• Wood studs (38/89mm) 20mm Gypsum both sides: 0.78
• 6mm double glass with air-gap: 0.7
• 75mm timber studs plastered both sides: 1.2

Reasonable range values can be calculated from engineering charts for sound transmission using this approximation: range = thickness * pow(2, -reductionDB/6) * 1024. Units are: range(m), thickness(m), reductionDB(dB). 1024 is 1/pow(2,-60[dB]/6).

Note: Double Sided Geometry To simulate a material like air-gap double window glass done using double sided model textures use “sound.transmission” with a value of 0.7 and a “thickness” of 0.1. This values are from the above table. This creates a material with constant sound transmission effect transmitting 1/7 of sound volume to the other side.

Note: No Transmission Loss To simulate a material with no transmission loss use sound.none if there is no absorption or a large value like 1000 if there is absorption.

The source is typically a single positive value or 0.

The default value for this texture property is 0.4.