Overview
IEC 61669:2015 (Edition 2) + AMD1:2025 - published by the International Electrotechnical Commission - is the international standard for measuring the real‑ear acoustical performance characteristics of air‑conduction hearing aids. It provides recommendations and requirements for test setups, signals, equipment, procedures and uncertainty assessment so that measurements made on a given hearing aid and human ear can be reliably reproduced across locations and test systems. This edition supersedes IEC 61669:2001 and ISO 12124:2001 and introduces technical updates such as the International Speech Test Signal and methods for real‑ear to coupler/dial differences.
Key topics and technical requirements
- Scope and reproducibility: Ensures repeatable real‑ear measurements and specifies limitations for devices using non‑linear or analytical processing (measurements are valid only for the specific test signals and conditions used).
- Real‑ear metrics defined: Procedures for measuring REAR (real‑ear aided response), REIG (real‑ear insertion gain), REUR/REUG (real‑ear unaided response/gain), REOR/REOG (occluded response/gain), RECD (real‑ear to coupler difference) and REDD (real‑ear to dial difference).
- Test equipment and setup: Requirements for probe‑microphone measurement systems, sound sources, equalization methods (substitution, modified pressure), signal levels, frequency and distortion limits, and ambient/test space acoustical properties.
- Probe microphone positioning: Guidance and informative Annex A on visual, acoustically‑assisted and geometrical positioning of the probe inlet at the measurement point.
- Measurement uncertainty and tolerances: Clause on estimating uncertainty and informative Annex C relating tolerance and acceptance intervals to permitted measurement uncertainty.
- Annex on RECD: Annex B discusses practical issues when measuring and applying RECD (important for coupling to coupler measurements and prescribing for infants/children).
Practical applications and users
Who uses IEC 61669:
- Audiologists and clinicians - validating hearing‑aid fittings and verifying aided sound levels in the ear.
- Hearing aid manufacturers and R&D labs - product development, QA, and performance verification under standardized conditions.
- Test laboratories and certification bodies - ensuring measurement traceability and conformity.
- Researchers and regulatory agencies - comparing device performance and establishing clinical best practices.
Typical applications:
- Verifying aided sound pressure levels for speech and test signals (REAR).
- Calculating insertion gain (REIG) to assess benefit over unaided condition.
- Using RECD to translate coupler measurements to real‑ear predictions - critical for pediatric fittings and for when real‑ear measurement is not feasible.
Related standards
Keywords: IEC 61669, real‑ear measurement, REAR, REIG, RECD, probe microphone, hearing aid testing, real‑ear acoustical performance.