St. Augustine's Cathedral had a magnificent pipe organ with a 32-foot rank — pipes so large that their fundamental frequency was 16 Hz, well below the threshold of human hearing. You couldn't hear it. You could definitely feel it.

During the new organist's first Easter service, she pulled out the 32-foot stop for the opening processional. Within minutes, congregants reported feeling dizzy, nauseous, and anxious. Two people left. One elderly gentleman described "a pressure in my chest like something sitting on it." The organist, perched in the loft and not directly in the affected zone, had no idea anything was wrong.

The room was the amplifier. The cathedral's nave was exactly 10.7 meters wide, producing an axial room mode at 16 Hz — precisely matching the organ pipe's fundamental. The standing wave created pressure zones where infrasound energy concentrated to SPL levels exceeding 100 dB. At 16 Hz, you don't hear sound — you feel pressure changes in your chest cavity, sinuses, and inner ear. Symptoms range from unease to nausea to genuine panic.

Infrasound at high SPL causes physiological responses because the body's organs have resonant frequencies in the 5-20 Hz range. The room mode turned a musical instrument into a resonance weapon.

The Moral: If your venue has symptoms but no audible cause, measure below 20 Hz. SonaVyx Transfer Function displays response down to the lowest frequencies, revealing infrasonic problems your ears can't detect.