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Pure-tone audiometry: procedure, transducers, bone conduction and pitfalls
Pure-tone audiometry finds, for each frequency, the threshold — the lowest level at which the listener responds to at least half of the presentations — by air and by bone conduction; a correct result depends on the right transducer, on calibration, and on spotting pitfalls such as the occlusion effect, vibrotactile responses, collapsing ear canals and acoustic radiation.
Why it matters in the exam
Questions on this topic are technical and precise: which transducer is calibrated with a 2-cc coupler (insert earphones) and which with a 6-cc coupler (supra-aural earphones), what a bone vibrator is calibrated with (an artificial mastoid), which transducer reaches above 8 kHz (circumaural earphones, for ototoxicity monitoring), and the advantage of mastoid over forehead placement (less energy is needed, so thresholds are lower). How long to present a tone — one to two seconds — and what counts as a significant change between two tests — 10 dB or more at the same frequency — are asked too.
A large part deals with pitfalls: the occlusion effect improves low-frequency bone-conduction thresholds when the canal is closed, and does not affect air conduction or an ear with a conductive loss; a response at low frequencies and high levels may be felt rather than heard, mainly in bone conduction; a canal that collapses under a supra-aural earphone in older adults creates a false air-bone gap, and the solution is insert earphones; and high-frequency, high-level bone conduction may "leak" into the air. Insert earphones are not recommended when the eardrum is perforated.
Key points
- Threshold = the lowest level with responses to at least half the presentations.
- 6-cc coupler for supra-aural, 2-cc for inserts, artificial mastoid for bone.
- Occlusion effect: bone, low frequencies, not with a conductive loss.
- Touch, radiation and collapsing canals create a false gap.
- A change of 10 dB or more at a frequency — significant.
Summary table
| Topic | What is true | Exam point |
|---|---|---|
| Threshold definition | The lowest level with responses to at least half of ascending presentations; down 10, up 5 | A tone of one to two seconds; a change of 10 dB or more is significant |
| Transducers and calibration | Supra-aural — 6-cc coupler; inserts — 2-cc; bone vibrator — artificial mastoid | Circumaural — above 8 kHz, for ototoxicity monitoring |
| Insert earphones | High interaural attenuation, prevent canal collapse, reduce the masking dilemma | Not recommended with a perforated eardrum |
| Bone conduction | Mastoid: lower thresholds than the forehead; crossover to the other ear cannot be prevented | Interaural attenuation for bone conduction is about zero |
| Occlusion effect | Closing the canal improves low-frequency bone thresholds | Does not affect air conduction or an ear with a conductive loss |
| Touch and radiation | Vibrotactile response at low frequencies and high levels (bone, or air at 250 Hz and 100 dB); acoustic radiation in bone conduction at high frequencies | Both create a false air-bone gap |
| Collapsing canal | In older adults, under a supra-aural earphone | A false high-frequency gap; retest with insert earphones |
A free exam question
A patient with a bilateral conductive loss has acoustic reflexes present in both ears. What is the next step?
- A. Refer to an ENT doctor
- B. Repeat the test with insert earphones
- C. The test is unreliable
In the full version for subscribers
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Sources
- Katz (ed.), Handbook of Clinical Audiology, 7th edition (2015) — Pure-tone air-conduction and bone-conduction testing
- ASHA Guidelines, 2005 — Guidelines for Manual Pure-Tone Threshold Audiometry
- ANSI S3.6, 2018 — Specification for Audiometers (calibration of transducers)
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.