What Are Tuning Forks Used For

Device that generates sounds of constant pitch when struck

Tuning fork past John Walker stamped with note (E) and frequency in hertz (659)

A tuning fork is an acoustic resonator in the form of a ii-pronged fork with the prongs (tines) formed from a U-shaped bar of rubberband metal (normally steel). It resonates at a specific abiding pitch when set vibrating by striking information technology confronting a surface or with an object, and emits a pure musical tone once the loftier overtones fade out. A tuning fork's pitch depends on the length and mass of the two prongs. They are traditional sources of standard pitch for tuning musical instruments.

The tuning fork was invented in 1711 by British musician John Shore, Sergeant trumpeter and lutenist to the court.^[1]

Description [edit]

Motion of an A-440 tuning fork (greatly exaggerated) vibrating in its primary mode

A tuning fork is a fork-shaped audio-visual resonator used in many applications to produce a fixed tone. The main reason for using the fork shape is that, unlike many other types of resonators, it produces a very pure tone, with about of the vibrational free energy at the fundamental frequency. The reason for this is that the frequency of the first overtone is about 5² / 2² = 25 / 4 = half dozen+ one⁄4 times the primal (virtually 2+ one⁄2 octaves higher up information technology).^[2] By comparison, the first overtone of a vibrating string or metal bar is one octave above (twice) the key, so when the string is plucked or the bar is struck, its vibrations tend to mix the cardinal and overtone frequencies. When the tuning fork is struck, lilliputian of the free energy goes into the overtone modes; they also die out correspondingly faster, leaving a pure sine wave at the key frequency. It is easier to tune other instruments with this pure tone.

Another reason for using the fork shape is that it can then be held at the base of operations without damping the oscillation. That is because its principal fashion of vibration is symmetric, with the 2 prongs always moving in opposite directions, and then that at the base where the 2 prongs come across there is a node (point of no vibratory motion) which can therefore be handled without removing energy from the oscillation (damping). However, in that location is still a tiny motility induced in the handle in its longitudinal direction (thus at correct angles to the oscillation of the prongs) which can exist fabricated audible using any sort of sound board. Thus by pressing the tuning fork's base against a sound board such every bit a wooden box, table top, or span of a musical instrument, this small motion, merely which is at a high acoustic pressure (thus a very high acoustic impedance), is partly converted into audible sound in air which involves a much greater motion (particle velocity) at a relatively depression pressure (thus low acoustic impedance).^[3] The pitch of a tuning fork can besides be heard straight through bone conduction, past pressing the tuning fork against the os only behind the ear, or even by holding the stem of the fork in one's teeth, conveniently leaving both easily complimentary.^[4] Bone conduction using a tuning fork is specifically used in the Weber and Rinne tests for hearing in club to featherbed the middle ear. If just held in open air, the sound of a tuning fork is very faint due to the acoustic impedance mismatch between the steel and air. Moreover, since the feeble audio waves emanating from each prong are 180° out of stage, those two opposite waves interfere, largely cancelling each other. Thus when a solid canvass is slid in betwixt the prongs of a vibrating fork, the apparent volume really increases, every bit this counterfoil is reduced, only as a loudspeaker requires a baffle in order to radiate efficiently.

Commercial tuning forks are tuned to the correct pitch at the mill, and the pitch and frequency in hertz is stamped on them. They tin be retuned past filing textile off the prongs. Filing the ends of the prongs raises the pitch, while filing the within of the base of operations of the prongs lowers it.

Currently, the most mutual tuning fork sounds the note of A = 440 Hz, the standard concert pitch that many orchestras use. That A is the pitch of the violin's second string, the beginning string of the viola, and an octave in a higher place the first cord of the cello. Orchestras between 1750 and 1820 mostly used A = 423.5 Hz, though there were many forks and many slightly unlike pitches.^[5] Standard tuning forks are available that vibrate at all the pitches within the central octave of the piano, and also other pitches.

Tuning fork pitch varies slightly with temperature, due mainly to a slight decrease in the modulus of elasticity of steel with increasing temperature. A alter in frequency of 48 parts per 1000000 per °F (86 ppm per °C) is typical for a steel tuning fork. The frequency decreases (becomes flat) with increasing temperature.^{[half dozen]} Tuning forks are manufactured to have their correct pitch at a standard temperature. The standard temperature is now 20 °C (68 °F), but xv °C (59 °F) is an older standard. The pitch of other instruments is also subject to variation with temperature alter.

Calculation of frequency [edit]

The frequency of a tuning fork depends on its dimensions and what it's made from:^[7]

f={\frac {i.875^{2}}{ii\pi l^{two}}}{\sqrt {\frac {EI}{\rho A}}},

where

f

is the frequency the fork vibrates at,

one.875 is the smallest positive solution of

cos(x) cosh(x) = -1

,^[8]

fifty

is the length of the prongs,

East

is the Young's modulus (elastic modulus or stiffness) of the material the fork is fabricated from,

I

is the second moment of surface area of the cantankerous-section,

ρ

is the density of the material the fork is made of,

A

is the cross-sectional expanse of the prongs (tines).

The ratio $I / A$ in the equation above can exist rewritten as $r ii /4$ if the prongs are cylindrical with radius $r$ , and $a ii /12$ if the prongs accept rectangular cantankerous-section of width $a$ forth the direction of motion.

Uses [edit]

Tuning forks have traditionally been used to tune musical instruments, though electronic tuners take largely replaced them. Forks can be driven electrically past placing electronic oscillator-driven electromagnets close to the prongs.

In musical instruments [edit]

A number of keyboard musical instruments use principles similar to tuning forks. The well-nigh popular of these is the Rhodes piano, in which hammers hit metal tines that vibrate in the magnetic field of a pickup, creating a point that drives electric amplification. The earlier, un-amplified dulcitone, which used tuning forks directly, suffered from low volume.

In clocks and watches [edit]

Quartz crystal resonator from a modernistic quartz watch, formed in the shape of a tuning fork. It vibrates at 32,768 Hz, in the ultrasonic range.

A Bulova Accutron sentry from the 1960s, which uses a steel tuning fork (visible in center) vibrating at 360 Hz.

The quartz crystal that serves as the timekeeping element in modern quartz clocks and watches is in the form of a tiny tuning fork. It usually vibrates at a frequency of 32,768 Hz in the ultrasonic range (above the range of human hearing). It is made to vibrate past pocket-size oscillating voltages applied to metal electrodes plated on the surface of the crystal by an electronic oscillator excursion. Quartz is piezoelectric, so the voltage causes the tines to bend rapidly back and along.

The Accutron, an electromechanical watch developed by Max Hetzel and manufactured past Bulova beginning in 1960, used a 360-hertz steel tuning fork as its timekeeper, powered by electromagnets attached to a battery-powered transistor oscillator circuit. The fork provided greater accuracy than conventional balance wheel watches. The humming sound of the tuning fork was audible when the watch was held to the ear.

Medical and scientific uses [edit]

ane kHz tuning fork vacuum tube oscillator used by the U.Due south. National Agency of Standards (now NIST) in 1927 every bit a frequency standard.

Alternatives to the common A=440 standard include philosophical or scientific pitch with standard pitch of C=512. According to Rayleigh, physicists and acoustic instrument makers used this pitch.^[9] The tuning fork John Shore gave to George Frideric Handel produces C=512.^[10]

Tuning forks, unremarkably C512, are used past medical practitioners to appraise a patient'south hearing. This is virtually commonly done with two exams chosen the Weber test and Rinne exam, respectively. Lower-pitched ones, usually at C128, are also used to check vibration sense equally function of the examination of the peripheral nervous system.^[eleven]

Orthopedic surgeons have explored using a tuning fork (lowest frequency C=128) to appraise injuries where os fracture is suspected. They hold the terminate of the vibrating fork on the skin above the suspected fracture, progressively closer to the suspected fracture. If there is a fracture, the periosteum of the bone vibrates and fires nociceptors (pain receptors), causing a local sharp pain.^{[ citation needed ]} This tin can indicate a fracture, which the practitioner refers for medical X-ray. The sharp pain of a local sprain tin give a fake positive.^{[ citation needed ]} Established practice, however, requires an Ten-ray regardless, considering it'southward improve than missing a real fracture while wondering if a response means a sprain. A systematic review published in 2014 in BMJ Open suggests that this technique is not reliable or accurate enough for clinical utilise.^[12]

Tuning forks also play a office in several culling therapy practices, such as sonopuncture and polarity therapy.^[13]

Radar gun calibration [edit]

A radar gun that measures the speed of cars or a brawl in sports is unremarkably calibrated with a tuning fork.^[xiv] ^[15] Instead of the frequency, these forks are labeled with the calibration speed and radar band (due east.thousand., X-band or K-ring) they are calibrated for.

In gyroscopes [edit]

Doubled and H-type tuning forks are used for tactical-grade Vibrating Structure Gyroscopes and diverse types of microelectromechanical systems.^[16]

Level sensors [edit]

Tuning fork forms the sensing part of vibrating point level sensors. The tuning fork is kept vibrating at its resonant frequency past a piezoelectric device. Upon coming in contact with solids, amplitude of oscillation goes down, the same is used as a switching parameter for detecting betoken level for solids.^[17] For liquids, the resonant frequency of tuning fork changes upon coming in contact with the liquids, change in frequency is used to find level.

References [edit]

^ Feldmann, H. (1997). "History of the tuning fork. I: Invention of the tuning fork, its course in music and natural sciences. Pictures from the history of otorhinolaryngology, presented by instruments from the collection of the Ingolstadt German Medical History Museum". Laryngo-rhino-otologie. 76 (two): 116–22. doi:x.1055/s-2007-997398. PMID 9172630.
^ Tyndall, John (1915). Sound. New York: D. Appleton & Co. p. 156.
^ Rossing, Thomas D.; Moore, F. Richard; Wheeler, Paul A. (2001). The Science of Sound (3rd ed.). Pearson. ISBN978-0805385656. ^{[ page needed ]}
^ Dan Flim-flam (1996). Teach Yourself to Play Mandolin. Alfred Music Publishing. ISBN9780739002865 . Retrieved 3 July 2015.
^ Fletcher, Neville H.; Rossing, Thomas (2008). The Physics of Musical Instruments (2nd ed.). Springer. ISBN978-0387983745. ^{[ page needed ]}
^ Ellis, Alexander J. (1880). "On the History of Musical Pitch". Journal of the Lodge of Arts. 28 (545): 293–336. Bibcode:1880Natur..21..550E. doi:x.1038/021550a0.
^ Han, Seon M.; Benaroya, Haym; Wei, Timothy (1999). "Dynamics of Transversely Vibrating Beams Using Four Engineering science Theories". Periodical of Sound and Vibration. 225 (5): 935–988. Bibcode:1999JSV...225..935H. doi:x.1006/jsvi.1999.2257. S2CID 121014931.
^ Whitney, Scott (23 April 1999). "Vibrations of Cantilever Beams: Deflection, Frequency, and Research Uses". University of Nebraska–Lincoln. Retrieved 9 November 2011.
^ Rayleigh, J. W. Due south. (1945). The Theory of Sound . New York: Dover. p. 9. ISBN0-486-60292-3.
^ Bickerton, RC; Barr, GS (December 1987). "The origin of the tuning fork". Periodical of the Royal Social club of Medicine. lxxx (12): 771–773. doi:10.1177/014107688708001215. PMC1291142. PMID 3323515.
^ Bickley, Lynn; Szilagyi, Peter (2009). Bates' guide to the concrete test and history taking (10th ed.). Philadelphia, PA: Lippincott Williams & Wilkins. ISBN978-0-7817-8058-2.
^ Mugunthan, Kayalvili; Doust, Jenny; Kurz, Bodo; Glasziou, Paul (4 August 2014). "Is there sufficient evidence for tuning fork tests in diagnosing fractures? A systematic review". BMJ Open up. 4 (viii): e005238. doi:10.1136/bmjopen-2014-005238. PMC4127942. PMID 25091014.
^ Hawkins, Heidi (August 1995). "SONOPUNCTURE: Acupuncture Without Needles". Holistic Wellness News.
^ "Calibration of Constabulary Radar Instruments" (PDF). National Bureau of Standards. 1976. Archived from the original (PDF) on 22 February 2012. Retrieved 29 Oct 2008.
^ "A detailed explanation of how police radars work". Radars.com.au. Perth, Australia: TCG Industrial. 2009. Retrieved 8 Apr 2010.
^ Proceedings of Anniversary Workshop on Solid-Country Gyroscopy (nineteen–21 May 2008. Yalta, Ukraine). Kyiv/Kharkiv: ATS of Ukraine. 2009. ISBN978-976-0-25248-5.
^ Vibrating Fork Level Sensor.