DnT,w (Standardized Level Difference)

DnT,w is the weighted standardized level difference between two rooms, the primary field measurement parameter for airborne sound insulation between rooms in a building. Defined in ISO 717-1:2020 and measured per ISO 16283-1, DnT,w accounts for the receiving room’s reverberation time through a standardization correction to a reference value of 0.5 s. This makes the result independent of the receiving room’s furnishing and allows comparison between measurements in different buildings. Higher DnT,w values indicate better sound insulation. Building regulations typically specify minimum DnT,w values: UK Building Regulations Approved Document E requires DnT,w ≥ 45 dB between dwellings, while higher values (50–55 dB) may be required for premium residential or sensitive use. Unlike laboratory Rw values, DnT,w includes all flanking transmission paths (structure-borne sound through floors, walls, and junctions), so field results are typically 5–10 dB lower than the separating element’s laboratory Rw rating.