Low-Frequency Impact Sound Insulation Descriptors Considering CLT Floors: ISO and ASTM Standards

Impact sound insulation performance is evaluated using weighted normalized impact sound pressure level (Ln,w) per ISO 717-2 and Impact Insulation Class (IIC) per ASTM E989, both measured using a standardized tapping machine in one-third-octave bands from 100-3150 Hz. Impact sounds below 100 Hz are correlated with subjective human annoyance. To account for low-frequency performance, these standards introduce additional descriptors, such as spectrum adaptation terms (CI,50-2500) in ISO and Low Impact Insulation Class (LIIC) in ASTM. Another test method involves the ISO rubber ball, which closely resembles the excitation of human hearing in the low-frequency range. The resulting spectrum performance is expressed by the standardized maximum impact sound pressure level (LAFmax,V,T). This study examines the correlation between low-frequency impact sound insulation descriptors in ISO and ASTM standards. Various laboratory-based impact sound insulation measurements were conducted on different CLT floor assemblies using both a standardized tapping machine and a rubber ball. ISO and ASTM acoustic descriptors are plotted against LAFmax,V,T. The results show a strong correlation between tapping machine and rubber ball measurements in ISO standards. However, no correlation is observed between LIIC and LAFmax,V,T. Finally, the necessity of considering both standards' descriptors in describing low-frequency impact sound performance is discussed.