Spatial Decay Rate

Spatial decay rate (D₂,S) is the rate of decrease in A-weighted sound pressure level per doubling of distance from a sound source in an open-plan office, measured at desk height (1.2 m). Defined in ISO 3382-3:2012 §4, D₂,S is the primary objective metric for open-plan office acoustics and correlates with speech privacy and distraction distance. The value is determined by linear regression of SPL measurements along a line extending from the source through multiple workstation positions. Higher D₂,S values indicate faster spatial attenuation and better acoustic conditions. Typical values range from 3 dB per distance doubling (poor, reverberant space) to 7+ dB per distance doubling (well-treated space with screens). D₂,S is improved by adding ceiling absorption, desk-height screens, and sound masking. The parameter integrates the combined effects of absorption, screening, and spatial layout into a single, measurable quantity.