Sound Insulation (Rw/STC)

Sound insulation is measured by establishing a sound field in a source room, measuring the sound pressure level on both sides of the partition under test, and computing the level difference corrected for the receiving room absorption. The result is a frequency-dependent sound reduction index R(f) that typically increases with frequency (mass law: +6 dB per doubling of frequency or surface density). Rw (weighted sound reduction index) is the international standard (ISO 717-1). The reference curve defined in ISO 717-1 Table 1 is shifted in 1 dB steps toward the measured R(f) data. The shift stops when the sum of unfavorable deviations (where the reference curve exceeds the measured values) first exceeds 32 dB. The Rw value is the value of the shifted reference curve at 500 Hz. Spectrum adaptation terms C and Ctr account for different noise spectra: C for pink noise (A-weighted traffic, living activities), Ctr for urban traffic noise (which has more low-frequency content). STC (Sound Transmission Class) is the North American equivalent (ASTM E413). The procedure is similar but uses different deficiency criteria: no single-band deficiency may exceed 8 dB, and the total deficiency must not exceed 32 dB. These differences mean Rw and STC can give slightly different ratings for the same partition — typically within 1-3 points. Typical values: standard drywall partition Rw 35-40, double stud wall Rw 50-55, concrete block wall Rw 45-50, mass-loaded vinyl barrier Rw 25-30, acoustic door Rw 35-45, double-glazed window Rw 30-38. Building codes typically require Rw 45-55 between dwellings. Field measurements (apparent sound reduction R') are always lower than laboratory values due to flanking transmission through floors, ceilings, and junctions. The difference can be 3-10 dB depending on construction quality. SonaVyx implements the ISO 717-1 reference curve shifting procedure and ASTM E413 STC calculation from 1/3-octave band measurement data.