The spectrum of the noise produced in the receiving room by the standard tapping machine is determined by (1) the size and the mechanical properties of the floor-ceiling assembly, such as its weight, surface properties, mounting or edge restraints, stiffness, and internal damping; (2) the degree of flanking transmission through associated structures; and (3) the acoustical response of the receiving room.

The standardized tapping machine specified in 6.1.1 produces a continuous series of uniform impacts at a uniform rate on a floor-ceiling assembly to allow accurate and reproducible measurements of impact sound pressure levels in the receiving room. The tapping machine is not designed to simulate any one type of impact, such as male or female footsteps or to simulate the weight of a human walker. Also, measurements described in this method and ratings based on the results are restricted to a specific frequency range. Thus the subjectively annoying creak or boom generated by human footfalls on a limber floor-ceiling assembly may not be adequately evaluated by this test method.

Laboratory Test Method E492 calls for highly diffuse sound fields and the suppression of flanking sound transmission in the laboratory's receiving room. This field test method does not allow efforts to suppress flanking. In field tests, acoustical measurements are much more uncertain than in the laboratory since a great variety of receiving room shapes and sizes are encountered in ordinary buildings. Highly diffuse fields are seldom found and the nature of structure-borne flanking transmission can vary widely; consequently, good agreement between laboratory tests and field tests on similar floor-ceiling assemblies should not be expected.

Several metrics are available for specific uses:

absorption normalized impact sound pressure level (ANISPL) and apparent impact insulation class (AIIC)-These metrics are intended to evaluate the performance of the floor-ceiling assembly and adjacent structures as installed (including structure-borne flanking paths). For these metrics, sound power from associated support structures are attributed to the floor-ceiling assembly. Because these are measures of the apparent performance of the nominally separating floor-ceiling, the receiving room shall be the space directly under the tapping machine. ANISPL and AIIC may be reported if the receiving room has a volume of at least 40 m³ and the smallest dimension is at least 2.3 m. ANISPL and AIIC may be measured and reported only if, in all frequency bands necessary to calculate the AIIC, the receiving room absorption, A₂, is less than:

Results are usually not identical to laboratory tests of the floor-ceiling assembly alone. Because of the uncontrollable factors mentioned in 5.1-5.3, caution must be used when using test results to predict the performance of other floor-ceiling assemblies with similar construction.

impact sound pressure level (ISPL) and impact sound rating (ISR)-These metrics are intended to assess the impact sound isolation as it exists at the time of the test due to the mechanical excitation of the floor-ceiling assembly by the standard tapping machine. The measurements can be performed in any space affected by the sound of the operating tapping machine. These metrics do not represent the performance of the separating floor-ceiling. They represent the impact sound isolation between the source floor and the receiving room. There are no receiving room absorption restrictions and no receiving room volume restrictions other than being sufficiently large to accommodate the microphone positions described in 10.3.

reverberation time normalized impact sound pressure level (RTNISPL) and normalized impact sound rating (NISR)-These metrics are intended to assess the impact sound isolation as if the receiving room had a reverberation time of 0.5 s. This reverberation time is typical of many furnished small offices and furnished residential living rooms and bedrooms. RTNISPL and NISR shall not be reported for receiving rooms of 150 m³ or larger.