Designed by Sir Christopher Wren and completed in 1710, the Whispering Gallery sits 30 meters above the cathedral floor. Its remarkable acoustic property relies on circular geometry and wave behavior known as Rayleigh waves or whispering-gallery waves. When a sound wave is produced near the circular wall, it does not scatter across the open air space of the dome.
Instead, the sound hits the smooth, concave stone wall at a shallow angle and reflects repeatedly around the circumference of the drum. Because the angle of incidence equals the angle of reflection, the acoustic energy remains trapped in a thin cylindrical shell hugging the wall. Lord Rayleigh first mathematically explained this phenomenon in 1878, demonstrating that higher-frequency sounds travel around the curve with remarkably little attenuation.
Today, the physics of whispering-gallery waves extends far beyond architecture, serving as a fundamental principle in quantum optics, micro-ring resonators, and optical sensors that trap light around micro-spheres.