Field airborne sound isolation in multifamily construction evaluation of metrics within ASTM E336

ASTM E336 defines several metrics describing airborne sound isolation for wall and floor/ceiling assemblies within multifamily dwellings. The standard mirrors the procedures for laboratory testing of sound transmission class (STC) in defining field STC (FSTC), which does not include flanking paths and is therefore virtually impossible to measure in the field. The current standard includes provisions for the measurements of apparent STC (ASTC) which include flanking paths, and field measurements within multifamily dwellings typically report ASTC even though applicable building codes require the reporting of FSTC. The standard also provides two noise reduction metrics, noise isolation class (NIC) and normalized NIC (NNIC). Analysis of the relationships of ASTC, NNIC, and NIC will be presented along with a survey of field test results and correlation with subjective reactions of occupants within multifamily dwellings. The analysis shows that the additional work required to determine the ASTC or NNIC is not warranted because it provides no additional useful data, and that the proper metric for evaluation of acoustical performance in the field for multifamily dwellings is NIC.