Terminal 3 had 127 ceiling speakers covering 40 gates. When the gate agent announced "Flight 847 to Denver has moved to Gate B2," what passengers heard was a warm, reverberant wall of vowels that could have been "Gate B2," "Late to Flu," or "Great debut." Thirty-seven passengers went to Gate D2. Fourteen went to Gate B12. Three went home.

The terminal's STI — Speech Transmission Index — measured 0.28 across the main concourse. IEC 60268-16 classifies anything below 0.30 as "bad," and anything below 0.45 as unsuitable for public address purposes. The airport was spending millions on a PA system that actively made communication worse than shouting.

The problem was layered. The terminal had a 12-meter ceiling with exposed steel deck (highly reflective), terrazzo floors (perfectly reflective), and glass curtain walls (guess). RT60 was 3.2 seconds. The ceiling speakers were spaced too far apart, creating alternating zones of coverage and shadow. Background noise from HVAC, rolling luggage, and general human chaos averaged 68 dBA, which the PA had to overcome on top of battling its own reverberation.

High-intelligibility PA in reverberant spaces requires distributed speakers close to listeners, directional coverage to minimize ceiling excitation, and time alignment to prevent cascade echoes between zones.

The Moral: Airports, stations, and hospitals need STI above 0.50 for safety. Measure with SonaVyx STI to quantify intelligibility and identify whether the problem is reverb, noise, or speaker placement.