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Tuning Fork

Tuning fork used in laboratory

1. What is tuning fork?
    1.1 Working principle of tuning fork
    1.2 History of tuning fork
2. Application of tuning fork
3. How to buy tuning fork?

What is tuning fork?

Tuning fork is a common experimental equipment in physics. It is a "Y"-shaped steel or aluminum alloy-sounding machine, which can produce a single wavelength of mechanical waves. Various tuning forks can emit different wavelengths of pure tones due to their size and the difference in the length and height of the fork arms. The longer the fork arm, the higher the tuning fork, the longer the wavelength; the "lower" the pitch, the shorter the fork arm, the shorter the tuning fork; the shorter the wavelength, the "higher" the pitch.

Tuning fork is made of flexible metal (mostly steel), with a handle at the end and forked at both ends, shaped like the Latin letter 'U'. The tuning fork has a fixed resonance frequency and vibrates when struck. After waiting for the initial overtone column to pass, the sound emitted by the tuning fork has a fixed pitch. The tuning fork’s pitch is determined by the length of its bifurcation.

Working principle of tuning fork

The mechanical waves emitted by the tuning fork after being struck are very weak and can only be heard clearly when taken to the ear. For this reason, sometimes the tuning fork will be pressed on a solid plane such as a table after the strike, which allows the plane to have the effect of a resonance plate, significantly increasing the amplitude energy.

A variety of tuning forks can be due to their mass and fork arm length, thickness, and differences in vibration emitting different frequencies of pure tones. It is resonance theory any object has an inherent frequency of oscillation, also called resonant frequency. When the object is placed in its inherent frequency, which is the resonant frequency environment, it will respond to the frequency, and can even vibrate at the same frequency.

History of tuning fork

Using a tuning fork in a medical situation, this tool is a very versatile tool that can be used for many different therapeutic procedures. For those who don't know, a tuning fork is a bifurcated metal fork that can be used as an acoustic resonator. Traditionally, the tuning fork has been used to tune musical instruments. The tuning fork matches the musician's instrument by releasing a perfect waveform. The same waveform can also be used in medical situations.

The tuning fork was invented in 1711 by the Englishman John Shore. He was a court trumpeter and the composers Georg Friedrich Handel and Henry Purcell both wrote passages in their compositions specifically for him to perform. He was also a luthier, which was very difficult to tune, and Scholl invented the tuning fork to tune the luthier.

The most common tuning fork used by musicians today is 440 Hz, which has long been used as a tuning standard for orchestras (in recent years tuning frequencies have gradually become more common at 442 Hz) because it is also the pitch of the second string of the violin (also known as the A string. The order is as follows: fourth string G, third-string D, second string A, first string E) and the pitch of the first string of the viola (fourth string C, third-string G, second string D, first string A). However, there are also a variety of other pitchforks on the market, such as those that produce all the pitches in the central part of the piano.

Application of tuning fork


The tuning fork

A tuning fork is a fork-shaped acoustic resonator that is used in many applications to produce a fixed tone. Unlike many other types of resonators, the main reason for using a fork shape is that it produces a very pure tone with most of the vibrational energy at the fundamental frequency. Another reason to use the fork shape is that it can be fixed to the base without damping the vibrations. That's because its main mode of vibration is symmetrical, with the two forks always moving in opposite directions, so there is a node at the base where the two forks intersect (the point where there is no vibrational motion), so it can be handled without removing energy from the oscillation (damping). However, in the longitudinal direction of the handle (and therefore at right angles to the oscillation of the fork-head), there is still a small movement that can be made using any type of sounding board. Thus, by pressing the bottom of the tuning fork against a soundboard, such as a wooden box, a tabletop, or the bridge of a musical instrument, this small movement, but which is at high sound pressure (and therefore very high acoustic impedance), is partly converted into audible sound in the air, involving greater motion (particle velocity) at relatively low pressure (and therefore low acoustic impedance). The pitch of a tuning fork can also be heard directly through bone conduction by pressing the fork against the bone behind the ear, or even by clenching the handle of the fork with the teeth and conveniently freeing the hands. Bone conduction using tuning forks was used specifically for Weber and Rinne hearing tests to bypass the middle ear. If just placed in the open air, the sound of the tuning fork is very weak due to the acoustic impedance mismatch between steel and air. In addition, since the weak sound waves emitted from each fork have a phase difference of 180°, these two opposite waves interfere and cancel each other out to a large extent. Therefore, when sliding a solid plate between the fork tines of a vibrating tuning fork, the apparent volume actually increases because this cancellation is reduced, just as a speaker needs a baffle for effective radiation.

Commercial tuning forks are factory tuned to the correct pitch, with pitch and frequency (in Hertz) stamped on them. They can be returned by filing the material of the pins. Filing the ends of the tines will raise the pitch while filing the inside of the bottom of the tines will lower the pitch.

A. Physical

In physics teaching, tuning forks can be used to demonstrate the nature of mechanical waves. Tapping the tuning fork to collect the wave spectrum. The test found that: lightly tapping the tuning fork, the amplitude of the tuning fork is small, the amplitude of the wave spectrum is small, and the sound from the tuning fork is also small; heavily tapping the tuning fork, the amplitude of the tuning fork is large, the amplitude of the wave spectrum is large, the sound from the tuning fork is also large. Note: The loudness of the mechanical wave is related to the amplitude of the tuning fork mechanical wave. The greater the amplitude, the greater the loudness; the smaller the amplitude, the less the loudness.

B. Electro-mechanical watch

The electro-mechanical watch was developed by Max Ezell for Bulova as the "Accutron". The watch used a 360Hz tuning fork and a battery, which provided a high degree of accuracy. In 1977, the production of this watch was discontinued.
The quartz oscillator contains a tiny quartz "tuning fork", which is most often used in modern quartz digital watches. The piezoelectric nature of the quartz crystal allows the quartz tuning fork to produce electrical pulses when it resonates and is therefore also used in computer chips for timekeeping. In today's watches, the resonance frequency of quartz is usually 32768Hz.

C. Medicine

In medicine, tuning forks for healing are also used to test a patient's hearing, the most common ones being C-256 and C-512. Longer wave tuning forks (e.g. C-64 and C-128) are used not only to test a patient's hearing but also as a sensory test of the peripheral nervous system. Tuning forks are also used as a therapeutic tool in some specific therapies such as sonopuncture.

D. Radar gun calibration

Radar guns are mainly used to measure the speed of a car or the speed of a ball in a sports competition, and are often calibrated using a mechanical wave fork as the mechanical wave source. These mechanical tuning forks have a fixed calibration speed rather than a wavelength. In addition, these mechanical tuning forks also have specific wavelengths (e.g., X-band or Y-band) that are used to calibrate a particular radar gun. Calibration mechanical tuning forks are calculated as Radar display speed = Radar wave frequency * Radar wave wavelength / 2 The above applies to all frequency band speed radar systems.

E. Industrial

Tuning fork level meter is a switch that controls the level. When working, the tuning fork is constantly in mechanical fluctuation, when an object touches the tuning fork, it will destroy the mechanical wave resonance, there is a current output inside the circuit, the output excitation current, then there is feedback when the destruction of the mechanical fluctuation, the circuit will identify, and then it can output a switch signal, which is a relay signal. The mechanical wave band of the tuning fork is in a band of 300Hz±50Hz.

How to buy tuning fork?

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