Audiometry and hearing tests — how you measure hearing
Pure tone audiometry dB HL and WHO classification of hearing loss
As an audiology assistant the hearing test is your most important tool. Pure tone audiometry is the most common method for measuring a person's hearing quantitatively and the result is plotted in an audiogram which shows the hearing threshold at different frequencies, cf. The Doctor's Manual on health.dk.
§Air line and ground line
With audiometry you play pure tones at different frequencies (typically from about 125 Hz to 8000 Hz) through headphones (air conduction) and find the weakest sound the patient can just hear at each frequency — the hearing threshold. By repeating the measurement with a bone vibrator behind the ear (bone conduction) which sends the sound directly to the inner ear bypassing the middle ear you and the doctor can see if hearing loss is caused by the middle ear (conductive hearing loss) or the inner ear/hearing nerve (sensorineural hearing loss).
§dB HL and WHO's classification of hearing loss
The hearing threshold is measured in decibel hearing level (dB HL) where 0 dB HL is the average normal hearing threshold for a young healthy ear at the given frequency — not a measure of the physical strength of the sound itself. Normal hearing is defined in WHO's 2021 classification as a threshold below 20 dB HL. The classification is based on the average of the thresholds at 0.5 1 2 and 4 kHz (PTA4) on the better-hearing ear and divides hearing loss into degrees with 15 dB increments.
| Grad (WHO 2021) | Average threshold (PTA4) |
|---|---|
| Degree 0 — normal hearing | under 20 dB HL. |
| Degree 1 — mild hearing loss | 20–34 dB HL |
| Degree 2 — moderate hearing loss | 35–49 dB HL |
| Degree 3 — moderate-severe hearing loss | 50–64 dB HL |
| Degree 4 — severe hearing loss | 65–79 dB HL |
| Degree 5 — very severe hearing loss | 80–94 dB HL |
| Degree 6 — deafness | 95 dB HL and above |
§Other central examinations
- 01Speech audiometry: the patient repeats words at different volumes so speech understanding can be assessed — not just tone hearing.
- 02Tympanometry: measures middle ear pressure and eardrum mobility and can reveal fluid in the middle ear or a perforated eardrum.
- 03Otoscopy: visual inspection of ear canal and eardrum with an otoscope before the actual hearing test is performed.
§Requirements for the test environment
Pure tone audiometry requires sound-isolated room or sound booth because even faint background noise can mask weak tones patient should respond to. You instruct patient to press button or raise hand as soon as tone is heard — even if very faint — and watch that patient understands and can complete test consistently
“An audiogram is not just a curve — it is the patient's experience of sound made measurable.”