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.
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 215 = 32,768 Hz. (See quartz clock.)
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.