Tuning Forks
A medical tuning fork is a two-pronged metal instrument that produces a tone at a defined frequency when struck. In clinical examination it is used in audiology, for tests comparing air and bone conduction, and in neurology, to assess vibration sense.
Quick summary: medical tuning forks are identified by their frequency, stamped on the stem. The three in routine use are 128 Hz, which is the neurological fork for vibration sense and is usually weighted; and 256 Hz and 512 Hz, which are the audiological forks used in bedside hearing tests, normally unweighted. Weights on the tines lower the frequency and lengthen the decay, which is why the neurological fork sustains longer. The practical point that affects both the result and the instrument is how it is struck: against a soft surface such as the heel of the hand or a rubber block, never against a hard edge, which introduces overtones and can distort the tines.
The three frequencies and what each is for
| Frequency | Usually | Field |
|---|---|---|
| 128 Hz | Weighted | Neurological examination, vibration sense |
| 256 Hz | Unweighted | Bedside hearing examination |
| 512 Hz | Unweighted | Bedside hearing examination |
The frequency is stamped on the stem of the fork, and it is the only way to identify one reliably: two forks of different frequency can look almost identical, and the difference in tine length is not obvious by eye.
Where an examination set is being assembled rather than a single fork replaced, sets are supplied covering several frequencies together, which is the usual arrangement for teaching and for a consulting room that carries out both types of examination.
Weighted and unweighted forks
This is the distinction that most often causes the wrong fork to be ordered, because it is not always stated in a product name.
A weighted fork carries mass at the tips of the tines. That lowers the frequency and, more importantly, lengthens the decay: the fork continues vibrating for longer after being struck. It is what the neurological fork needs, because the assessment involves the vibration being felt over a period rather than heard as a tone.
An unweighted fork produces a cleaner tone with a shorter decay, which suits the audiological tests where what matters is a clear pitch rather than sustained vibration.
Some neurological forks carry graduated weights that allow the intensity of the vibration to be read on a scale as it decays, rather than only recorded as present or absent.
How the fork is struck
It is the part of the technique that affects both the measurement and the life of the instrument, and it is almost never written down.
A fork is struck against a soft, yielding surface — the heel of the hand, a rubber block, the knee. Striking it against a hard edge such as a table, a door frame or a metal trolley does two things: it introduces overtones, so the fork is no longer producing a single clean frequency, and over time it deforms the tines, at which point the fork no longer sounds at its stamped frequency.
A fork that has been repeatedly struck against hard surfaces looks intact. Nothing on it indicates the problem, which is why a fork of uncertain history is worth replacing rather than trusting.
The second point of technique is that the fork is held by the stem. A hand touching the tines damps the vibration immediately and shortens the decay, which in a vibration-sense assessment changes what is being measured.
Aluminium and steel
Both materials are used and the difference shows over time rather than at first use.
Aluminium is lighter and the more common choice for sets, which matters when several forks travel in a case. Steel is denser, holds its pitch more reliably through years of use and resists deformation better.
In either case the fork is a solid instrument with no moving parts and no coating on the working surfaces, which is what allows it to be cleaned and processed between patients according to the setting's protocol.
Where the fork sits in the examination
Tuning forks belong to the bedside examination set rather than to instrumented measurement.
Where hearing thresholds need to be established rather than compared, that is done with an audiometer, and where assessment is regular, inside an audiometric booth. The fork does not replace either: it is the instrument available at the bedside, in a home visit or wherever an examination happens without a controlled environment.
Alongside it, otoscopes cover the examination of the ear canal and eardrum that normally precedes any hearing assessment. The rest of the examination set is in diagnostic material.
Which tests are performed, how and what the findings mean are matters for the clinician carrying out the examination.
What to check before buying
- The frequency, stamped on the stem, and whether a set or a single fork is needed
- Weighted or unweighted, according to whether the use is neurological or audiological
- Graduated weights, if the vibration intensity is to be read on a scale
- Material, aluminium for a portable set, steel for durability in fixed use
- Case or holder, since forks in a bag knock against each other
Frequently asked questions
Which tuning fork frequencies are used in clinical examination?
Three are in routine use: 128 Hz, which is the neurological fork for assessing vibration sense and is usually weighted, and 256 Hz and 512 Hz, which are the audiological forks used in bedside hearing examination and are normally unweighted. The frequency is stamped on the stem of the fork.
What is the difference between a weighted and an unweighted fork?
A weighted fork carries mass at the tips of the tines, which lowers the frequency and lengthens the decay so the fork keeps vibrating for longer after being struck. That is what the neurological fork needs, because the vibration is felt over a period rather than heard as a tone. An unweighted fork produces a cleaner tone with a shorter decay, which suits the audiological tests.
How should a tuning fork be struck?
Against a soft, yielding surface such as the heel of the hand, a rubber block or the knee. Striking it against a hard edge — a table, a door frame, a metal trolley — introduces overtones, so the fork no longer produces a single clean frequency, and over time deforms the tines, at which point it no longer sounds at its stamped frequency. A fork damaged this way looks entirely intact.
Why does it matter how the fork is held?
Because a hand touching the tines damps the vibration immediately and shortens the decay. The fork is held by the stem, and in a vibration-sense assessment, where the decay is part of what is being observed, damping it changes the observation.
Aluminium or steel tuning forks?
Aluminium is lighter and the more common choice for sets, which matters when several forks travel in a case. Steel is denser, holds its pitch more reliably through years of use and resists deformation better. The difference shows over time rather than at first use.
What are graduated weights on a tuning fork for?
They allow the intensity of the vibration to be read on a scale as it decays, rather than being recorded only as present or absent. They appear on neurological forks intended for that type of assessment.
Do tuning forks replace an audiometer?
No. A tuning fork is part of the bedside examination set: it allows air and bone conduction to be compared without instrumentation. Establishing hearing thresholds is done with an audiometer, and where assessment is regular, inside an audiometric booth. The fork is what is available at the bedside, on a home visit or wherever an examination takes place without a controlled environment.
How are tuning forks cleaned?
They are solid instruments with no moving parts and no coating on the working surfaces, which allows them to be cleaned and processed between patients according to the protocol of the setting and the manufacturer's instructions.