Chapter 2 — The audiogram

Pure-tone audiometry: dB HL, air and bone, masking, configurations.

The audiogram is the central tool of clinical audiology. Almost every other test in this book — speech audiometry, tympanometry, OAEs, hearing-aid fitting, cochlear-implant candidacy — is read in the context of the audiogram. This chapter develops it carefully across four lessons.

We start with the test itself — pure-tone audiometry in 2.1 — and the chart that results. We then unpack the units on the y-axis (2.2): dB SPL, dB HL, dB SL, dB(A), and why audiometry chose the one it did. We examine air conduction vs. bone conduction and what the gap between them reveals (2.3). And we close with the procedural problem the audiometer faces — cross-hearing — and the masking procedure that corrects for it, plus the standard taxonomy of audiogram configurations (2.4).

• 2.1 Pure-tone audiometry — what the test is, what the chart looks like, how thresholds are recorded.
• 2.2 Decibels: SPL, HL, SL — four decibel scales an audiologist uses, the RETSPL table that links them, why the audiogram uses dB HL.
• 2.3 Air and bone conduction — what BC measures, the air-bone gap, conductive vs. sensorineural vs. mixed loss.
• 2.4 Masking and audiogram configurations — the cross-hearing problem, the plateau method, and the standard taxonomy (sloping, notched, flat, cookie-bite).