Description Tuning fork

tuning fork john walker stamped note (e) , frequency in hertz (659)



a needle on tuning fork carves figures on carbon black.

a tuning fork fork-shaped acoustic resonator used in many applications produce fixed tone. main reason using fork shape that, unlike many other types of resonators, produces pure tone, of vibrational energy @ fundamental frequency. reason frequency of first overtone 5/2 = 25/4 =  6 ⁄4 times fundamental (about  2 ⁄2 octaves above it). comparison, first overtone of vibrating string or metal bar 1 octave above (twice) fundamental, when string plucked or bar struck, vibrations tend mixture of fundamental , overtone frequencies. when tuning fork struck, little of energy goes overtone modes; die out correspondingly faster, leaving pure sine wave @ fundamental frequency. easier tune other instruments pure tone.

another reason using fork shape that, when vibrates in principal mode, handle vibrates , down prongs move apart , together. there node (point of no vibration) @ base of each prong. handle motion small, user can hold fork handle without damping vibration, handle can still transmit vibration resonator, amplifies sound of fork. user typically strikes fork, , presses handle against wooden box resonator, table top, edge of musical instrument, or behind ear. if held in open air, sound of tuning fork faint. sound waves each prong 180° out of phase other, @ distance fork interfere , largely cancel each other out. if sound-absorbing sheet slid in between prongs of vibrating fork, reducing waves reaching ear 1 prong, volume increases, due reduction of cancellation.

commercial tuning forks tuned correct pitch @ factory, , pitch , frequency in hertz stamped on them. can retuned filing material off prongs. filing ends of prongs raises pitch, while filing inside of base of prongs lowers it.

currently, common tuning fork sounds note of a = 440 hz because standard concert pitch, because many orchestras use standard. pitch of violin s second string, first string of viola, , octave above first string of cello. orchestras between 1750 , 1820 used frequency of a = 423.5 hz, though there many forks , many different pitches. standard tuning forks available vibrate @ pitches within central octave of piano, , other pitches. well-known tuning fork manufacturers include ragg , john walker, both of sheffield, england.

tuning fork pitch varies temperature, due slight decrease in modulus of elasticity of steel increasing temperature. change in frequency of 48 parts per million per °f (86 ppm per °c) typical steel tuning fork. frequency decreases (becomes flat) increasing temperature. tuning forks manufactured have correct pitch @ standard temperature. standard temperature 20 °c (68 °f), 15 °c (59 °f) older standard. pitch of other instruments subject variation temperature change.