ISO 389-1:2017

Overview

ISO 389-1:2017 - Acoustics - Reference zero for the calibration of audiometric equipment (Part 1) defines the reference equivalent threshold sound pressure levels (RETSPLs) used to calibrate pure‑tone air‑conduction audiometers with supra‑aural earphones. The standard provides internationally agreed reference zero values and model‑specific data to ensure uniform expression of hearing threshold levels across laboratories, clinics and manufacturers.

Key topics and technical requirements

• Scope: RETSPLs for pure tones measured with supra‑aural earphones; intended for direct application in audiometer calibration.
• Normative references: IEC 60318‑1 (ear simulator for supra‑aural/circumaural earphones) and IEC 60318‑3 (acoustic coupler).
• Generic vs model‑specific data:
  • Use model‑specific RETSPLs when available (reduces uncertainty). Examples included: Sennheiser HDA 280, Telephonics TDH 39, Beyer DT 48, RadioEar DD 45.
  • If unavailable, apply the generic RETSPL table for supra‑aural earphones measured on an IEC 60318‑1 ear simulator.
• Design and coupling requirements for earphones to qualify for the generic dataset: axial symmetry, specific cushion/contact geometry, effective contact diameter (25 mm), acceptable cushion deformation under load, and a headband static force (generic: 4.5 N ± 0.5 N).
• Measurement conditions: coaxial coupling, vertical axis, no acoustic leakage, specified static force. Values are rounded to the nearest 0.5 dB.
• Example RETSPLs (generic, reference 20 µPa): 1 kHz = 7.5 dB, 125 Hz = 45 dB, 8 kHz = 15.5 dB.

Applications and who uses this standard

ISO 389-1:2017 is essential for:

• Audiology clinics and hearing test centers - to calibrate audiometers for accurate hearing threshold measurement.
• Calibration laboratories - to certify audiometric equipment against internationally recognized RETSPLs.
• Audiometer and earphone manufacturers - to design and validate equipment compatibility with ear simulators and couplers.
• Occupational health and regulatory bodies - to ensure consistent reporting of hearing thresholds for compliance and epidemiology.
• Research institutions performing controlled audiometric studies requiring standardized reference levels.

Related standards

• IEC 60318‑1: Ear simulator for supra‑aural/circumaural earphones (used for RETSPL measurement)
• IEC 60318‑3: Acoustic coupler for supra‑aural earphone calibration
• ISO 389 series (other parts define RETSPLs for different transducers and conditions)

Notes: Annex A in the standard gives guidance on applying RETSPLs; Annex B explains derivation and data sources. Use model‑specific RETSPL tables where available to minimise calibration uncertainty.