Sounds of Silence: Achieving Sound-reduced Flooring in Multi-Floor Buildings

Testing for Airborne Sound (STC Rating)

In layman’s terms, the STC rating determines approximately how much the existing floors, walls and/or ceilings in a room reduces (or “attenuates”) sound transmission. The industry test standard for STC ratings is ASTM E90, from ASTM International.

The following testing method summary is provided courtesy of NGC Testing Services, one of the most sophisticated, fully accredited, independent testing facilities in North America. However, the ASTM procedures are standard.

1. To conduct the STC test, loudspeakers are placed in a room, called the Source Room, with their locations determined by the spatial and statistical requirements of ASTM E90.
2. Microphones are placed in the Source Room and in a room beneath, referred to as the Receiving Room. The microphone locations in this room are also determined per ASTM E90 requirements.
3. A Random Noise field is produced using the loudspeakers in the Source Room, and measurements are taken at each microphone location in each room.
4. The difference between the two rooms’ average sound levels is measured, with the difference being corrected to account for the Receiving Room’s sound absorption. The resulting number is the Transmission Loss, which is used to calculate the STC value. The higher the STC rating, the better the reduction of airborne noise.

The typical minimum building code requirement for STC protection is 50. However, this number can change from area to area.

Testing for Impact Sound (IIC and Delta IIC)

The industry test standard for IIC sound ratings is ASTM E492. As with the STC testing information, the following steps are provided courtesy of NGC Testing Services, but the ASTM procedures are standard.

1. To conduct these tests, a tapping machine with steel-faced hammers is placed in the Source Room at four well-defined locations on the existing floor / ceiling assembly.
2. Microphones are placed in the room beneath, referred to as the Receiving Room, at specific locations per spatial and statistical requirements of ASTM E492.
3. Tapping-machine hammers strike the floor of the Source Room, and the sound levels in the Receiving Room are measured and averaged.
4. The average sound levels measured in the Receiving Room are corrected to account for the Receiving Room’s sound absorption. These levels are applied to a standard IIC curve, and the IIC value is calculated. The higher the IIC rating, the better the reduction of impact noise. As with STC requirements, the typical minimum building code requirement for IIC sound ratings is 50. This number, however, can change from area to area.

Testing for Delta IIC is essentially the same as for testing IIC, with the same measurement test procedure being used as in IIC measurement. However, there are differences.

First, the main structure over which test samples are tested is a 6" (15 cm) standard concrete floor without any material installed but a floor covering.

Second, the Delta IIC rating is calculated differently than the IIC rating: The differences in measured impact sound levels are subtracted from the levels historically defined in the standard, and these differences are then used to calculate the Delta IIC rating.