tuning fork
A tuning fork (outdated Diapason ) is a metal fork , the prongs of which produce a clear, overtone- poor sound when struck . The tuning fork was invented in 1711 by the trumpeter and lutenist John Shore .
principle
Sound generation
From a physical point of view, the tuning fork is a flexural oscillator . The tines swing in opposite directions when striking. As soon as the tines move outward, the air in front of them is compressed while it is diluted between them. When swinging back, the density distribution is reversed. We perceive the pressure differences that spread out in waves as sound .
The generated sinusoidal oscillation can be made visible in various ways, for example with the help of a stroboscope or a microphone and oscilloscope . If you attach a needle to one of the prongs and quickly pull it over a soot-blackened glass plate after striking it, the waveform of the oscillation is drawn into the soot - provided that suitable alignments are made.
Reinforcement
If the foot (handle) of a struck tuning fork is pressed axially sufficiently firmly onto a large-area body that can be stimulated to oscillate, such as a table top (in its center), the (transverse) oscillation of the tuning fork via the extremely small stroke oscillation of the foot via the large area of the plate converted into airborne sound more efficiently . Higher volume becomes audible, but the higher energy dissipation from the fork means that it fades away much faster .
If you press the fork foot on the top of the skull, the ear is also efficiently addressed via the transmission of structure-borne sound .
As a teaching aid , tuning forks are often built on a small rectangular wooden box with rubber feet at the lower corners. This means that the fork is both elevated and a standardized implementation in airborne sound is offered. The somewhat elongated, rather flat (L: W: H = approx. 4: 2: 1) wooden box is typically open on both small ends. This results - depending on the pitch - in a somewhat more forward and backward direction of sound propagation. If the audience looks into the sound opening, they should also see the "U" on the tuning fork.
Suggestion
A frequently performed experiment on resonance in physics is based on two tuning forks attached to decoupled resonance bodies and calibrated to the same frequency : If a tuning fork is struck and stopped a few seconds later, the tone will still sound; the second tuning fork was stimulated to vibrate at its natural frequency by the sound wave emitted by the first .
use
In music
Tuning forks tuned to a concert pitch are used to tune musical instruments and when making music. In male choirs , tuning forks in F ' tuning are also occasionally used.
In the medicine
Tuning forks are also used in medicine in several areas.
In neurology , tuning forks are used to test the vibration sensation , the pallesthesia , by setting them in low vibrations (64 Hz) and placing them on places where a protruding bone is quite superficial, for example the big toe joint or the ankle . If the vibration is absent, neuropathy is suspected .
Due to the very simple examination and the inexpensive instrument, it is a good examination method for diabetic polyneuropathy as part of the disease management program in general medicine . The variant according to Rydel-Seiffer is used here , in which one can objectively measure the vibration sensation by means of scaled weights.
In audiology , simple, orienting hearing tests can be carried out using tuning forks . The best known are certainly the Weber experiment and the Rinne experiment , which can be used to make rough statements about the localization of the fault.
In mechanics
The governor for setting the engine speed of a teleprinter was adjusted with the help of a tuning fork. In addition, the controller was painted alternately with black and white fields. At each end of the tuning fork there was a plate with a small slot. If you looked through these slots with the tuning fork struck, the stroboscopic effect resulted in a stationary image of the white areas of the rotating controller at the correct speed .
Electronic tuning forks in clocks
Electronic tuners do not necessarily generate tones, but they can always measure the tones generated by the instrument. In quartz watches one's clock crystal for 32,768 Hz built, from which by simple frequency division by 2 15 can be derived second pulses. Since quartz is very hard, the resonance frequency of a crystal block a few millimeters in size is much too high in the megahertz range.
Thanks to the tuning fork shape, a quartz rod that is twice as long can be accommodated with the same length, and the size is so small that the quartz fits into a watch case despite the low resonance frequency. In addition, rods with bending vibrations that are attached to one of their ends or in their middle would transfer a relatively large amount of vibration energy to their attachment due to their shifting of mass when they swing, and therefore vibrate strongly, while with the tuning fork shape the shifting of mass due to the mutual oscillation of the two halves the tuning fork is largely compensated.
Before wristwatches became more precise by counting quartz oscillations , Bulova brought a watch with a visible and audible tuning fork called Accutron to the market for greater accuracy .
Vibration probe
The vibration probe is used to measure fill levels in containers . It works on the principle of the tuning fork.
See also
