Audiometers
An audiometer generates calibrated tones at defined frequencies and intensities to establish hearing thresholds. This section covers the instrument together with its transducers — air conduction headphones, bone conductor, noise-attenuating cups and the operator intercom — which are part of the measuring system rather than optional extras.
Quick summary: pure-tone audiometry is performed across the range from 125 Hz to 8 kHz, and an audiometer is specified by the frequencies it generates, the intensity range at each one, whether it supports bone conduction as well as air conduction, and whether it can apply masking to the non-test ear. The point that most affects a purchase is that the transducers are calibrated together with the audiometer as one system: headphones cannot be swapped between units, or replaced individually, without recalibrating. And an audiometer out of calibration produces results that look entirely normal, which is why the calibration schedule is part of owning one rather than an afterthought.
Screening and diagnostic audiometers
Instruments in this field fall into two classes, and the difference is what they can measure rather than how well.
| Criterion | Screening | Diagnostic |
|---|---|---|
| Purpose | Detect whether thresholds fall outside expected levels | Establish thresholds precisely |
| Air conduction | Yes | Yes |
| Bone conduction | Usually not | Yes |
| Masking | Usually not | Yes |
| Speech audiometry | No | On models that support it |
| Typical setting | Occupational health, school screening | Audiology and ENT |
The dividing line is bone conduction and masking. Without them an instrument establishes that hearing differs from expected levels; with them it can separate where in the auditory pathway that difference arises. Which class a setting needs follows from the assessments it carries out.
Why masking exists
It is the function that most distinguishes a diagnostic instrument, and the reason is physical rather than clinical.
When a tone is presented loudly enough to one ear, it can be perceived by the other — sound crosses the head. Without controlling for that, a threshold recorded for one ear may in fact have been heard by the other. Masking presents a controlled noise to the non-test ear so the measurement isolates the ear under test.
An instrument without masking cannot resolve that situation, which is why it belongs to the screening class regardless of how many frequencies it generates.
The transducers are part of the calibrated system
This is the point that changes how the equipment is bought and maintained, and it is rarely stated on a product page.
An audiometer is calibrated with the specific transducers it will be used with. The calibration establishes what output the instrument must produce, through that particular headset, to deliver a given level at the ear. Different headphones have different acoustic characteristics, so the calibration belongs to the combination, not to the instrument alone.
Three practical consequences follow. Headphones cannot be swapped between audiometers. A damaged headset cannot simply be replaced with an equivalent one and put back into service. And when transducers are replaced, the system is recalibrated as a unit.
It is also why the transducers in this section are listed against the instrument they belong to rather than as generic accessories.
Air conduction, bone conduction and attenuating cups
Each transducer serves a distinct measurement.
Air conduction headphones deliver the tone through the ear canal and are the standard route for threshold testing. Bone conduction headphones place a vibrator against the mastoid, bypassing the outer and middle ear, which is what allows the two pathways to be compared.
Noise-attenuating cups — audiocups — enclose the air conduction headphones in an outer shell that reduces ambient noise reaching the ear. They are the alternative where testing takes place outside a booth, or the supplement where the room is borderline, and they attenuate rather than replace the environment.
The intercom or monitor completes the setup where the patient is inside an enclosure and the operator outside: it carries instructions in and the patient's responses out.
Calibration
An audiometer is a measuring instrument, and it drifts.
The characteristic that makes this consequential is that drift produces no symptom: the instrument switches on, generates tones and records thresholds exactly as before, and only the values are wrong. There is no fault to notice.
Calibration is therefore periodic rather than reactive, and the interval, the procedure and who may carry it out are set by the requirements applicable to the setting and the activity, together with the manufacturer's instructions. It is worth establishing the arrangement before purchase rather than after, because it recurs for the life of the instrument.
Two related checks: whether calibration data can be stored in the instrument, and whether the manufacturer or supplier provides a service route in the UK, since the instrument leaves the clinic while it is being done.
The test environment
The measurement is only as good as the environment allows, because ambient noise sets a floor below which thresholds cannot be established.
Where assessment is regular, that environment is an audiometric booth, and the audiometer sits outside it with the transducers passing through the jack panel — which is why the number of connections on that panel has to cover the transducer set in use, bone conductor and patient response button included.
For bedside or basic examination outside that setting, tuning forks remain part of the standard set, and otoscopes cover the examination that normally precedes audiometry. The rest of the consulting room equipment is in diagnostic material.
What to check before buying
- Frequency range and intensity range generated at each frequency
- Bone conduction and masking, which determine screening or diagnostic class
- Which transducers are included and which are supplied separately
- Calibration route: who performs it, where, and how the instrument is handled meanwhile
- Connections required at the booth jack panel for the full transducer set
- Output and data handling: printout, storage or transfer of results
Audiometric assessment, the interpretation of results and the conditions under which testing is performed are matters for the audiology professional and for the requirements applicable to the activity and the setting.
Frequently asked questions
What is an audiometer?
An instrument that generates calibrated tones at defined frequencies and intensities in order to establish hearing thresholds. Pure-tone audiometry is performed across the range from 125 Hz to 8 kHz, and the instrument is specified by the frequencies it generates, the intensity range at each, and whether it supports bone conduction and masking in addition to air conduction.
What is the difference between a screening and a diagnostic audiometer?
The dividing line is bone conduction and masking. A screening instrument establishes that hearing differs from expected levels; a diagnostic one adds bone conduction and masking, which allow the measurement to separate where in the auditory pathway that difference arises. Speech audiometry is available on diagnostic models that support it.
Why is masking needed?
Because sound crosses the head. When a tone is presented loudly enough to one ear it can be perceived by the other, so a threshold recorded for one ear may in fact have been heard by the other. Masking presents a controlled noise to the non-test ear so the measurement isolates the ear under test. An instrument without masking cannot resolve that situation.
Can I use any headphones with an audiometer?
No. An audiometer is calibrated with the specific transducers it will be used with, because the calibration establishes what output the instrument must produce through that particular headset to deliver a given level at the ear. Different headphones have different acoustic characteristics, so the calibration belongs to the combination rather than to the instrument alone. Headphones cannot be swapped between audiometers, and a damaged headset cannot be replaced and returned to service without recalibrating the system.
What is the difference between air and bone conduction transducers?
Air conduction headphones deliver the tone through the ear canal and are the standard route for threshold testing. Bone conduction headphones place a vibrator against the mastoid, bypassing the outer and middle ear, which is what allows the two pathways to be compared. Both are part of a diagnostic setup.
What are audiocups for?
They are noise-attenuating cups that enclose the air conduction headphones in an outer shell, reducing the ambient noise reaching the ear. They are used where testing takes place outside a booth, or as a supplement where the room is borderline. They attenuate the environment rather than replace it.
How often does an audiometer need calibrating?
Calibration is periodic rather than reactive, and the interval, the procedure and who may carry it out are set by the requirements applicable to the setting and the activity, together with the manufacturer's instructions. The reason it matters is that drift produces no symptom: the instrument switches on, generates tones and records thresholds exactly as before, and only the values are wrong. It is worth establishing the arrangement before purchase, because it recurs for the life of the instrument.
Does an audiometer need a sound booth?
The measurement is only as good as the environment allows, because ambient noise sets a floor below which thresholds cannot be established. Where assessment is regular, that environment is an audiometric booth, with the audiometer outside and the transducers passing through the jack panel. Where testing is occasional or takes place off site, attenuating cups reduce ambient noise reaching the ear without replacing a controlled environment.