If a sound absorbing sheet is slid in between the prongs of a vibrating fork, reducing the waves reaching the ear from one prong, the volume heard will actually increase, due to a reduction of this cancellation.Īlthough commercial tuning forks are normally tuned to the correct pitch at the factory, they can be retuned by filing material off the prongs. The reason for this is that the sound waves produced by each fork prong are 180° out of phase with the other, so at a distance from the fork they interfere and largely cancel each other out. Without the resonator (which may be as simple as a table top to which the handle is pressed), the sound is very faint. The handle motion is small, allowing the fork to be held by the handle without damping the vibration, but it allows the handle to transmit the vibration to a resonator (like the hollow rectangular box often used), which amplifies the sound of the fork. There is a node (point of no vibration) at the base of each prong. It is easier to tune other instruments with this pure tone.Īnother reason for using the fork shape is that, when it vibrates in its principal mode, the handle vibrates up and down as the prongs move apart and together. So when the fork is struck, little of the energy goes into the overtone modes they also die out correspondingly faster, leaving the fundamental. By comparison, the first overtone of a vibrating string or metal bar is only one octave above the fundamental. The reason for this is that the frequency of the first overtone is about 5 2/2 2 = 25/4 = 6¼ times the fundamental (about 2½ octaves above it). The main reason for using the fork shape is that, unlike many other types of resonators, it produces a very pure tone, with most of the vibrational energy at the fundamental frequency, and little at the overtones ( harmonics). Tuning fork by John Walker stamped with note (E) and frequency in hertz (659) File:Tuning fork on carbon black.jpgĪ needle on a tuning fork carves figures on carbon black. The tuning fork was invented in 1711 by British musician John Shore, Sergeant Trumpeter and Lutenist to the court. They were a standard feature of early psychology laboratories but have been superceded by the electric tone generator. Its main use is as a standard of pitch to tune other musical instruments. The pitch that a particular tuning fork generates depends on the length of the two prongs. It resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object, and emits a pure musical tone after waiting a moment to allow some high overtones to die out. Tuning fork on resonance box, by Max Kohl, Chemnitz, GermanyĪ tuning fork is a piece of apparatus, an acoustic resonator in the form of a two-pronged fork with the prongs (tines) formed from a U-shaped bar of elastic metal (usually steel).
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