acoustics

A microphone is a transducer that converts pressure waves in air into electrical signals, and there are at least six fundamentally different ways to accomplish that conversion, each with trade-offs in sensitivity, ruggedness, and frequency response.

On August 27, 1883, the island of Krakatoa in Indonesia exploded with a sound estimated at 310 decibels at source — the loudest sound ever produced on Earth's surface by any event in the historical record. The pressure wave circled the globe four times. It ruptured eardrums of sailors 64 kilometers away, was heard in Rodrigues Island near Mauritius 4,800 kilometers distant, and registered on barometers across the world. On January 15, 2022, the eruption of Hunga Tonga-Hunga Ha'apai produced the loudest infrasound event of the modern era, with pressure waves detectable globally. These events reveal something surprising: there is a hard physical ceiling on how loud a sound in air can ever be — 194 decibels — and Krakatoa probably exceeded it.

Hermann von Helmholtz formulated energy conservation, invented the ophthalmoscope, measured nerve impulse speed, and trained Heinrich Hertz. His full biography and science.

Sound is invisible, yet it shapes how we experience the world. Understanding it means diving into wave physics, the Doppler effect, and the strange world of ultrasound.

From Pythagoras to Bach to electronic music, mathematics has always been running under music. Here's how ratios, waves, and arithmetic create harmony and rhythm.