Impact Sound Pressure Levels ratings#
IIC#
IIC (Impact Insulation Class) is a single number rating for floors. It is calculated or derived from 1/3 octave band Normalised Impact Sound Pressure Level data by a method described in American Society for Testing Materials standard ASTM E989. This rating method was developed to predict performance for footfall and other impact type sounds.
Tip
The higher the IIC value for a floor construction, the better its impact insulation performance.
To determine the IIC rating, a standard-shaped rating curve (the blue curve on the INSUL Graph) is slid down from above until the sum of the deviations of the green test curve above the blue curve add up to just less than 32. In addition, the deviation between the green test curve and the blue rating curve must not be greater than 8 in any 1/3 octave band. By looking at where the green curve (the Normalised Impact Sound Pressure Level) is above the blue curve (the IIC curve) one can tell what frequencies are determining the IIC rating.
The IIC rating can be applied to any type of floor construction (including concrete and timber floor constructions). However, care should be taking when comparing IIC ratings for different constructions. For example, concrete and timber floor constructions sharing a common IIC value can, subjectively, sound quite different from each other.
Ln,w#
Ln,w is an alternative single number rating for floors. Like the IIC rating, Ln,w uses 1/3 octave band Normalised Impact Sound Pressure Level data, but derives its rating in accordance with ISO standard (ISO 717/2).
Hint
The higher the Ln,w value for a floor construction, the worse its impact insulation performance.
Note that this is the converse of the IIC rating system.
To determine the Ln,w rating, a standard shaped curve (the blue curve on the graph) is slid down from above until the sum of the deviations of the green test curve above the blue curve add up to just less than 32. There is no restriction on the size of a deviation at a single 1/3 octave band being less than 8, as there is with the IIC method.
Frequency range#
Both the IIC and Ln,w ratings are evaluated over the frequency range 100-3150 Hz.
IIC and Ln,w ratings for a given floor construction vary from each other considerably and must not be compared directly to each other to evaluate performance.
Toggle between IIC and Ln,w#
To switch between the IIC (ASTM) and Ln,w (ISO) ratings either:
- Click the Rating itself
- Go into Settings and change the rating and/or the frequency range
