This blog post explores the influence of the tuning fork’s invention on music and science, and examines the origin of the 440Hz standard pitch.
A tuning fork is made by bending a metal bar of uniform thickness into a U-shape and firmly welding a metal pillar to its lower end. This device produces a sound of a specific frequency when struck with a small hammer. Generally, the smaller the tuning fork, the higher the pitch it produces. Such tuning forks are widely used not only in music but also in scientific experiments, establishing themselves as crucial tools for studying the physical properties of sound.
Originally, the tuning fork was developed in 1711 by John Shore, an English trumpet player, as a tool to produce a reference pitch when tuning instruments. At that time, instrument tuning relied heavily on the player’s ear, inevitably leading to inaccuracies. While the invention of the tuning fork greatly improved the accuracy of instrument tuning, initially it was only known that the tuning fork produced specific notes on keyboard instruments; the number of vibrations per second (Hz) of these notes was unknown. Instruments tuned using these tuning forks thus had slightly different reference pitches depending on the region and the player, due to the lack of precise measuring devices at the time.
Determining the frequency of a tuning fork was a very difficult problem. This problem was solved by the German acoustician Johann Scheibler in 1834. Scheibler used a method of counting the beat frequency produced by two tuning forks vibrating at different frequencies. Battement refers to the phenomenon where two sounds with slightly different frequencies interfere, causing the sound to periodically grow louder and softer. The battement frequency produced when two tones with different frequencies sound together corresponds to the difference in their frequencies. A battement frequency of about 4 times per second, or 4Hz (hertz), is suitable for measurement by ear.
Beating is one of the interference phenomena of sound and plays an important role in both music and physics. For example, when two tones have nearly identical frequencies, beating occurs, causing the sound to periodically alternate in intensity. This phenomenon arises because the frequencies of the two tones are nearly the same and is one of the key concepts in acoustics.
Schiebler’s experiment required multiple tuning forks. He adjusted the first tuning fork to produce a note equivalent to the A note on a keyboard instrument, and the second tuning fork to be slightly larger, ensuring their beat frequency was 4Hz. This means the first tuning fork’s natural frequency was 4Hz higher than the second. Next, Schiebler created a larger third tuning fork. He tuned it so that when struck together with the second tuning fork, it also produced four beats per second. Thus, the third tuning fork had a frequency 8Hz lower than the first. Schaebler repeated this method, creating new tuning forks until he produced one that sounded exactly one octave lower than the first tuning fork. Ultimately, the 56th tuning fork produced a tone exactly one octave lower than the first. Schiebler calculated that the 56th tuning fork produced a vibration frequency 4Hz × 55, or 220Hz, lower than the 1st tuning fork.
Since it was already known that the vibration frequency of the higher note in a pair of notes one octave apart is twice that of the lower note, Schiebler could easily calculate the tuning fork’s natural frequency. The natural frequency of the No. 1 tuning fork is twice that of the No. 56 tuning fork, and the difference is 220Hz. Therefore, the natural frequency of the No. 1 tuning fork is 440Hz, and that of the No. 56 tuning fork is 220Hz.
Building on this achievement, Schaeuble proposed at a 1834 scientific conference in Stuttgart, Germany, that the A note on keyboard instruments be standardized at 440Hz. The resulting ‘Stuttgart pitch’ subsequently became widely adopted as the tuning standard across many European countries. This standardized instrument tuning throughout Europe significantly contributed to enhancing consistency in musical performance and education. In modern times, 440Hz remains the standard tuning pitch, demonstrating the profound importance of Schiebler’s achievement.
