Tuning fork

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A tuning fork is an acoustic resonator in the form of a two-pronged fork with the tines formed from a U-shaped bar of elastic metal (usually steel). 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. The pitch that a particular tuning fork generates depends on the length of the two prongs.

Explanation

Currently, the most common tuning fork used by musicians sounds the note of A (440 Hz, international "concert pitch"), which has long been used as a standard tuning note by orchestras, it being the pitch of the violin's second string played open, the first string of the viola played open, and an octave above the first string of the cello, again played open. However, they are also commercially made to vibrate at frequencies corresponding to all musical pitches within the central octave of the piano, and other pitches.

The tuning fork was invented in 1711 by John Shore, Sergeant Trumpeter to the court, who had parts specifically written for him by both George Friderich Handel and Henry Purcell.

The reason for using the fork shape is that, when vibrating, there is a node in the vibration pattern at the bend of the 'U' where the handle is attached, so the handle doesn't vibrate. This allows it to be held there without damping the vibration.

When struck, it gives out a very faint note which is barely audible unless held close to the ear. For this reason, it is sometimes struck and then pressed down on a solid surface such as a desk which acts as a sounding board and greatly amplifies the note.

Well-known manufacturers of tuning forks include Ragg and John Walker, both of Sheffield, England.

Calculation of frequency

The frequency of a tuning fork depends on its dimensions and the material from which is made:

f  propto frac{1}{l^2} sqrt{frac{AE}{rho}}

, and where the tines are cylindrical,

f  = frac{R}{pi l^2} sqrt{frac{E}{rho}}

Where:

f is the frequency the fork vibrates at
A is the cross-sectional area of the tuning fork
l is the length of the fork's tines
E is the Young's modulus of the material the fork is made from
ρ is the density of the material the fork is made from
R is the radius of the tines

Uses

They are commonly used to tune musical instruments, although electronic tuners also exist, and some musicians have perfect pitch. Tuning forks can be tuned by removing material off the tines (filing the ends of the tines to raise it or filing inside the base of the tines to lower it) or by sliding weights attached to the prongs. Once tuned, a tuning fork's frequency varies only with changes in the elastic modulus of the material; for precise work, a tuning fork should be kept in a thermostatically controlled enclosure. Large forks are often made to be driven electrically, like an electric bell or buzzer, and can vibrate for an indefinite time.

In musical instruments

A number of keyboard musical instruments using constructions similar to tuning forks have been made, the most popular of them being the Rhodes piano, which has hammers hitting constructions working on the same principle as tuning forks.

In electromechanical watches

Electromechanical watches developed by Max Hetzel for Bulova used a 360 Hertz tuning fork with a battery to make a mechanical watch keep time with great accuracy. The production of the Bulova Accutron, as it was called, ceased in 1977.

A tiny quartz tuning fork is used in crystal oscillators, the most notable use of which are quartz digital watches. The piezoelectric properties of quartz crystals cause a quartz tuning fork to generate a pulsed electrical current as it resonates, which is used by the computer chip in the watch to keep track of the passage of time. In today's watches, they generally resonate at $2^{15}=32,768$ Hz. (See quartz clock.)

Medical uses

Tuning forks, usually C-512, are used by medical practitioners to assess a patient's hearing. Lower-pitched ones (usually C-128) are also used to check vibration sense as part of the examination of the peripheral nervous system. They are also used therapeutically in sonopuncture.

John Beaulieu, a researcher on the therapeutic benefits of tuning forks, has recorded an album of music made entirely with tuning forks, called Calendula. Dr. John Beaulieu discovered BioSonic Repatterning while sitting in an anechoic chamber in New York University, and recognized the vibration patterns that correlated to musical notes at different octaves. He tried tuning forks at different octaves and could feel his body aligning with the tones. Other researchers into the therapeutic benefits of tuning forks, including Arden Wilken and Jack Wilken.

One system of alternative therapy developed by Francine Milford, is called Tuning Fork Therapy(R). Online correspondence courses are offered to allow for training and practitioners to be certified in this alternative healing therapy. These and other courses are available through the Reiki Center of Venice (Florida).

Radar gun calibration

A radar gun, typically used for measuring the speed of cars or balls in sports, is usually calibrated with tuning forks. Instead of the frequency, these forks have the calibration speed and radar band (e.g. X-Band or K-Band) for which they are calibrated.

References

External links

http://www.onlinetuningfork.com, an online tuning fork using Macromedia Flash Player.

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Last updated on Thursday March 13, 2008 at 07:15:01 PDT (GMT -0700)
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