Field impact insulation testing: Inadequacy of existing normalization methods and proposal for new ratings analogous to those for airborne noise reduction

The field test method for determining the Field Impact Isolation Class (FIIC) rating of a floor/ceiling assembly, prescribed in ASTM E 1007, requires an estimation of the receiving room absorption and the normalization of the receiving room sound pressure levels based on a standard quantity of room absorption. Normalization is intended to remove the effects of receiving room acoustical characteristics, but an analysis of field impact testing indicates that this method has a limited engineering value. The normalization correction is strongly dependent on receiving room volume, does not correlate with the normalization used in airborne sound isolation testing, and can be unreasonably large under certain conditions. The current test method leads to potential errors in engineering judgment, as illustrated by example field tests. By contrast, airborne noise reduction ratings (prescribed in ASTM E 336) are either non-normalized or normalized to a standard reverberation time, which provides significant advantages over normalizing to a standard amount of absorption. New impact noise metrics, the non-normalized impact sound rating (ISR) and the normalized impact sound rating (NISR), analogous to the airborne noise reduction metrics NIC and NNIC, are proposed for incorporation into ASTM E 1007. Revised building code requirements using the proposed metrics are suggested.