Edison’s Phonograph

Sound moves a diaphragm and stylus.

A horn gathers sound pressure and directs it toward a thin diaphragm. The changing air pressure makes the diaphragm vibrate. A stylus attached to the diaphragm therefore moves with the same time-varying pattern.

The stylus presses into a cylinder covered with wax or a thin layer of tinfoil. As a handle turns, the cylinder rotates and also advances slowly along its axis. The stylus cuts a continuous helical groove whose small variations encode the original vibration.

The groove drives the mechanism backward.

For playback, the stylus follows the recorded groove. The groove's variations move the stylus, which vibrates the diaphragm. The horn couples that vibration back into the air so the listener hears an approximation of the recorded sound.

No electrical amplification is required in this early machine. The system is a mechanical transducer, storage medium and reproducer.

A simple principle demanded accurate motion.

The cylinder's rotation, axial travel, stylus pressure and groove spacing had to remain aligned. Too much friction damaged the recording; unstable speed changed pitch; poor tracking destroyed fidelity. The phonograph was therefore a triumph of precision engineering, not merely a clever sketch.