A tuning fork, formed of a two-pronged fork, is an acoustic resonator with prongs formed from a U-shaped bar of elastic metal. When struck against a surface it resonates at a specific constant pitch emitting a pure musical tone after waiting a moment for some high overtones to die out. The length of the prongs determines the particular pitch of the fork. Most of the time it is used as a standard of pitch to tune other musical instruments.
In 1711, John Shore invented the tuning fork. The fork produces a very pure tone and is therefore used often to tune instruments. Most of the vibrational energy is at the fundamental frequency and little at the overtones as is not normal with other resonators.
Since the handle of the fork has very little vibration one can hold the fork without dampening the vibration, but it allows the handle to transmit the vibration to a resonator. Without the resonator, the sound is very faint. If a sound absorbing sheet is put between the prongs reducing the waves reaching the ear from one prong the sound heard will actually increase. Prongs are usually tuned to the correct pitch at the factory; however, pitch can be changed by filing material off the prongs. Take material off the end of the prongs raises the pitch, while filing the inside base lowers it.
The most common tuning fork now sounds the note of A = 440 Hz which is the standard concert pitch. It is the pitch of the violin’s second string, the first string of the viola, and an octave above the first string of the cello, all played open. Well-known manufacturers of tuning forks include Ragg and John Walker, both of Sheffield, England.