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IEC 60318-2: Acoustic Couplers — The “Artificial Ear” Calibrating Hearing Aids and Headphones
Why Headphone Reviews Disagree: The Answer Lies in the Artificial Ear Coupler Design
IEC 60318-2:1998 specifies acoustic couplers — the “artificial ears” used to calibrate supra-aural headphones and hearing aids. The ±5 dB discrepancy between headphone frequency response measurements from different labs fundamentally traces back to whether the coupler accurately replicates human ear canal acoustic impedance.
| Coupler Type | Headphone Type | Simulated Volume | Frequency Range |
|---|---|---|---|
| IEC 60318-1 (Ear Simulator) | Insert earphones (IEM), hearing aids | 1.26 cm³ (closed canal) | 100Hz–10kHz |
| IEC 60318-2 (Coupler) | Supra-aural (On-Ear) | 6 cm³ | 100Hz–8kHz |
| IEC 60318-3 (Artificial Ear) | Circumaural (Over-Ear) | Includes pinna + canal | 20Hz–20kHz |
Using the wrong coupler — e.g., a 2 cm³ cavity for supra-aural headphones — artificially boosts low-frequency response by 10–15 dB, producing a completely erroneous frequency response curve. The coupler choice is the single most consequential decision in headphone measurement.
TNLab — Headphone measurement is not just “plug in a microphone.” Choose the wrong artificial ear type, and the entire frequency response is distorted.