Municipal Pool Lifeguard Training, Chapter 12: "Use the PA system to give clear safety instructions." Nobody told Chapter 12 about the acoustic properties of indoor swimming pools.

The pool hall had a barrel-vaulted concrete ceiling, tile walls, tile floor, and a 25-meter water surface that reflected sound as efficiently as glass. The RT60 was 6.2 seconds. When the lifeguard pressed the PA button and said "No running on the deck," what the swimmers heard was a thunderous, overlapping roar that sounded approximately like "NNOOO RRRUUUNNNIIINGG ONNNN THHHEE DEEECCCKKKK" where each syllable smeared into the next with a six-second tail.

The STI was 0.15 — classified as "unintelligible" even by generous standards. During an emergency drill, the evacuation message was so garbled that swimmers reported hearing everything from "fire in the parking lot" to "free parking for everyone." One child thought the lifeguard was announcing snack time and headed for the vending machines.

Indoor pools combine every acoustic nightmare: massive volume, all hard surfaces, a large water reflector, and typically a curved ceiling that focuses sound into caustic patterns. They consistently rank among the worst acoustic environments for speech.

The Moral: If RT60 exceeds 4 seconds, speech reinforcement requires specialized distributed systems with minimal distance between speaker and listener. Measure with SonaVyx RT60 to understand what you're working with before installing a PA.