Field normalization techniques and practices for determining sound isolation and impact insulation

Abstract

The International Building Code (IBC) includes minimum acceptable acoustical performance for floor/ceiling assemblies separating dwelling units. Field tests for determining the Normalized Noise Isolation Class (NNIC) and Field Impact Insulation Class (FIIC) of an assembly require the measurement of the decay rate of the receiving room and the normalization of the sound pressure levels, as set forth in ASTM standards E336 and E1007. The normalization is intended to improve comparability of test results by removing the effects of receiving room absorption. Surprisingly, the normalization procedure is substantially different between these two types of tests. The FIIC normalization is based on the laboratory Impact Insulation Class (IIC) test using a standard room absorption of 10 metric sabins. The NNIC normalization is based on a 0.5-s reverberation time, which is assumed normal in a furnished habitable dwelling space. This difference in normalization procedure for the same receiving room potentially yields different results of NNIC and FIIC as compared with their respective non-normalized values. This will be illustrated with examples of actual field tests. The effectiveness and suitability of the normalization procedures in the field setting are compared and evaluated including the use of the California Building Code modification to FIIC.