ISO 389-2:1994

Overview

ISO 389-2:1994 defines the reference equivalent threshold sound pressure levels (RETSPL) for pure-tone audiometry when using insert earphones. It supplements the RETSPLs in ISO 389:1991 (to be re-issued as ISO 389-1) by providing calibrated reference levels specifically applicable to the Etymotic Research ER-3A insert earphone coupled with ER-3-14 ear inserts. The standard establishes a traceable reference zero for the calibration of audiometric equipment using acoustic couplers (IEC 126) and occluded-ear simulators (IEC 711).

Key topics and technical requirements

• Defines RETSPL values (dB re 20 μPa) for pure tones up to 8 kHz for:
  • Acoustic coupler conforming to IEC 126
  • Occluded-ear simulator conforming to IEC 711
• Applies to ER-3A insert earphones coupled by ER-3-14 ear inserts; includes physical coupling details:
  • Foam eartip nominal diameter 13 mm, length 12 mm
  • Internal plastic tube nominal internal diameter 1.9 mm, effective length specified
  • Outer eartip positioned 2–3 mm inside ear canal entrance
  • Total effective tube length (earphone output to ear insert simulator) determined as 251 mm
• Measurement and data notes:
  • RETSPL values rounded to the nearest 0.5 dB; some frequencies derived by interpolation
  • Values derived from three independent experimental investigations (see annex A); averaged without subject-number weighting
  • Data are for calibration of pure-tone audiometers and the production of consistent, reproducible audiometric thresholds
• Includes definitions for ear insert, insert earphone, ear simulator, occluded-ear simulator and acoustic coupler

Practical applications

• Calibration and verification of audiometric equipment that use insert earphones to ensure accurate hearing thresholds
• Laboratory calibration procedures for manufacturers of audiometers, hearing aids, and insert earphone devices
• Hearing conservation and occupational audiometry programs that require consistent, standardized reference levels
• Clinical audiology where insert earphones are preferred (to reduce occlusion and interaural effects) and traceable calibration is required

Who uses this standard

• Audiologists and clinical hearing professionals
• Acoustic and test engineers in audiometry equipment manufacturing
• Calibration laboratories and conformity assessment bodies
• Regulatory agencies and occupational health programs

Related standards

• ISO 389-1 (re-issue of ISO 389:1991) - RETSPL for supra-aural earphones
• ISO 389 parts 3–7 (bone vibrators, masking noise, high-frequency RETSPLs, short-duration signals, free-field thresholds)
• IEC 126 (acoustic coupler for insert earphones), IEC 711 (occluded-ear simulator), IEC 318, IEC 303

Keywords: acoustics, audiometry, audiometric equipment, calibration, RETSPL, insert earphones, ER-3A, ER-3-14, IEC 126, IEC 711, reference zero.