Variations in sound insulation from 20 Hz in lightweight dwellings

The objective of this study is to quantify the total variations in impact and airborne sound insulation from 20 and 50 Hz, respectively, within a wood-based building system. Field measurements in 70 rooms have been statistically analyzed, in weighted metrics and in third octave bands. Since 1994, the Swedish building code permits wood-based high-rise multifamily dwellings. However, the low frequency sound insulation soon turned out to be insufficient, and complaints were more common in lightweight buildings compared to traditional heavy constructions. Therefore, in 1999, the extended frequency range 50-3150 Hz was introduced in the requirements, an action that mitigated the problem, but only to some extent. Consequently, the lightweight industry often aims one sound class (4 dB) higher than the minimum requirements to obtain satisfactory performance. The Swedish research program Aku20 (2014-2017) showed that the correlation between measured and perceived impact sound insulation in lightweight constructions was significantly improved, when even lower frequencies (20-50 Hz) were included. In this context, the variations of low frequency field measurements and corresponding safety margins need to be investigated.