Improved low-frequency sound measurements for impact insulation class (IIC) rating using a comparison technique

Abstract

In multistory buildings, the isolation of sound from floor to ceiling is a major concern. The building codes use an impact insulation class (IIC) rating defined by ASTM to characterize the acoustical performance of floorâ–“ceiling assemblies due to impacts. The measurement process defined in this standard has repeatability and reproducibility limitations due to low-frequency, non-diffuse sound fields in receiving rooms. A comparison method is proposed in this article that uses a reference sample with known sound power to calculate the room or path contribution to the measured sound pressure level, which is then used to calculate the sound power of the floorâ–“ceiling assembly. The proposed method is tested for a small-scale hardboard plate, and the test results are within 1 to 2 dB of baseline sound power values. A simply supported plate used as the reference plate showed MAC values higher than 0.9 for analytical and experimental mode shapes. The analytical natural frequencies are within 1% to 2% of experimental frequencies and analytical sound power values are within 1-2 dB of experimental data. This study showed that for a small-scale assembly, the new methodwas able to characterize the room contribution within 1 to 2 dB.