Impact Insulation ClassIIC

The Impact Insulation Class (IIC) is a laboratory rating much like the Sound Transmission Class; however, it represents the isolation provided by a floor system subjected to a controlled impulsive load. Since there is no standard footstep, the impulsive loads are generated by a tapping machine pictured in Fig. 12.6. The machine consists of a frame supporting a row of five cylindrical hammers, each weighing a half-kilogram (1.1 lbs), which are raised by a cam mechanism and dropped sequentially from a height of 4 cm (1.6 in) onto the surface of the floor. The cam is driven by an electric motor that is set to deliver 10 impacts per second at equal intervals.

There are test standards in the United States and Europe that regulate the laboratory (ASTM E 492 and ISO 140/6) as well as field (ASTM E 1007 and ISO 140/7) test methodologies. The test is performed by placing the tapping machine near the center of the

Figure 12.6 Tapping Machine Showing Inner Workings

Figure 12.6 Tapping Machine Showing Inner Workings

hammers

Figure 12.7 IIC Tapping Machine Positions

floor under test. Spatially averaged sound pressure levels are then measured in the room below in third-octave bands ranging from 100 through 3150 Hz. The readings are done for four specified tapping machine positions illustrated in Fig. 12.7. A normalized impact sound pressure level in the receiving room is then obtained from the spatial average sound pressure levels

The absorption in the receiving room is measured either by using the reverberant field approximation (Eq. 12.2) and a source of known sound power, or by measuring the reverberation time, from which the total absorption is obtained using the Sabine equation.

where Lp = average one - third octave sound pressure level measured in the receiving room (dB)

Lw = one - third octave sound power level of the reference source (dB)

R = sound absorption in the receiving room (m2 or ft2 ) A0 = reference absorption in the same units as R (either 10 metric sabins or

108 sabins) K = 0.1 for SI units or 10.5 for FP units

0 0

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