First Baptist Church had a main floor PA system and a separate pair of speakers for the 200-seat balcony. The balcony speakers were fed from the same mix bus with no delay compensation. The balcony seats were 27 meters from the main PA speakers, meaning the direct sound from the mains arrived 80ms after the main floor heard it.

During congregational singing, the main floor started on time with the piano. The balcony heard the piano 80ms late and sang 80ms behind the floor. The main floor heard the balcony singing behind them and unconsciously slowed down. The balcony heard the floor slowing down and slowed further. Within 30 seconds, the hymn had split into a round that Bach never intended. The worship leader, standing at the front with both in-ear monitors and acoustic bleed from the balcony, was hearing a canon for two congregation parts and looked increasingly alarmed.

The balcony speakers needed to arrive at the balcony seats slightly before the main PA's acoustic energy reached them — using the Haas precedence effect to localize the sound to the balcony speakers while the main PA energy arrived within the integration window. Instead, the balcony speakers and the main PA both arrived at the balcony at different times, creating a 40ms echo.

Balcony fill speakers require delay equal to the propagation time from the mains to the balcony.

The Moral: If your congregation sings in rounds when they shouldn't be, you have a delay problem. Use SonaVyx Transfer Function to measure propagation time from mains to balcony and set your delay speakers accordingly.