Impact sound transmission

Picture of tapping machine Impact sound transmission tests are carried out using a standard tapping machine that incorporates 5 steel-faced hammers. These are driven by a motor so they strike the floor being tested 10 times per second. The tapping machine is placed in several positions on the floor and the impact sound pressure levels are measured in the room below in the frequency range 100 to 3150 hertz. The details of the machine and the measurement procedures are described in ASTM E492, Standard Test Method for Laboratory Measurement of Impact Sound Transmission through Floor-ceiling Assemblies using the Tapping Machine. The sound pressure levels are used to calculate IIC as described in ASTM E989, Standard Classification for Determination of Impact Insulation Class (IIC).

To obtain the single-number ratings, a reference contour is used  in a procedure that is analogous to that for Airborne Sound Transmission Loss. The contour extends from 100 to 3150 Hz. The measured 1/3 octave band impact sound pressure levels are fitted to the contour subject to the following rules:

Fitting IIC contour to data
  • Deviations occur when a measured value (red bars) is greater than the contour (blue line).
  • The contour is adjusted until sum of deviations <=32. For IIC, no individual deviation may be greater than 8 dB.
  • The IIC value is read from the contour value at 500 Hz using the right hand axis.

The IIC rating increases as the impact sound insulation improves.

Impact insulation can also be measured in buildings according to ASTM E1007, Standard Test Method for Field Measurement of Tapping Machine Impact Sound Transmission through Floor-ceiling Assemblies and Associated Support Structures. The test procedure and calculations are essentially the same as E492, the laboratory test, but the rating is called Field Impact Insulation - FIIC