Privacy Index (PI)

The Privacy Index (PI) quantifies the degree of speech privacy between two spaces as a percentage, calculated as PI = (1 − AI) × 100, where AI is the Articulation Index. PI ranges from 0% (perfectly intelligible, no privacy) to 100% (completely unintelligible, perfect privacy). Per ASTM E1130, a PI of 95% or above indicates confidential privacy (suitable for legal, medical, and HR offices), while 80–95% provides normal privacy (suitable for general offices). PI below 60% is considered unacceptable for any office requiring speech confidentiality. The PI metric provides an intuitive percentage-based expression that is easier for non-specialists to understand than the Articulation Index. PI is affected by the partition’s STC rating, flanking paths (ceiling plenum, ducts, doors), the source voice level, and the receiving room’s background noise level (including sound masking). Improving any of these factors increases the PI value.