ISO 389-8:2004

Overview - ISO 389-8:2004 (Acoustics, RETSPL for circumaural earphones)

ISO 389-8:2004 specifies reference equivalent threshold sound pressure levels (RETSPLs) for pure tones from 125 Hz to 8 kHz for use in the calibration of air-conduction audiometers fitted with a specific circumaural earphone model - the SENNHEISER HDA 200. The standard provides the reference values (Table 1), notes on derivation (Annex A), measured sound attenuation of the HDA 200 (Annex B) and correction figures to obtain free-field equivalent outputs for speech audiometers (Annex C). Values are derived from multi-laboratory studies and are intended to standardize audiometric calibration and reporting.

Key topics and technical requirements

• Scope: RETSPLs for pure tones 125 Hz–8 kHz specifically for the HDA 200 circumaural earphone.
• Calibration setup: Use the ear simulator and adapter specified in IEC 60318-1 and IEC 60318-2 as indicated in the standard.
• Reference values: Table 1 gives RETSPLs (values rounded to 0.5 dB). Example values from the standard: 125 Hz ≈ 30.5 dB, 1 kHz ≈ 5.5 dB. Some frequencies are interpolated.
• Environmental and mechanical conditions: Calibrate near 21 °C to 25 °C; maintain headband force of 10.0 N ± 1.0 N with earphone placement dimensions as specified.
• Annex B (attenuation): Provides measured sound attenuation of HDA 200 across octave bands (example: 1 kHz ≈ 28.5 dB).
• Annex C (free-field corrections): Correction figures to convert coupler measurements to free-field equivalent levels - useful for speech audiometry (IEC 60645-2 types A–E and B–E).

Applications and who uses ISO 389-8

• Audiology clinics and hearing-care professionals: ensures consistent audiometer calibration for reliable pure-tone threshold testing.
• Calibration laboratories and metrology institutes: use RETSPLs and prescribed coupler/adapter setup to verify and certify audiometric equipment.
• Manufacturers of audiometers and earphones: validate design and provide conformity data for device calibration.
• Occupational health and hearing conservation programs: maintain standardized test conditions and measurement traceability.

Practical value: follow the standard to reduce inter-laboratory variability, ensure accurate threshold measurements, and apply Annex C corrections when converting to free-field speech levels.

Related standards

• ISO 389 series (Parts 1–9), especially ISO 389-1 and ISO/TR 389-5 (extended high frequency).
• ISO 4869-1 (hearing protector attenuation measurement).
• IEC 60318-1 / IEC 60318-2 (ear simulators and couplers).
• IEC 60645-2 (speech audiometers).

Keywords: ISO 389-8:2004, RETSPL, audiometer calibration, circumaural earphone, SENNHEISER HDA 200, acoustics standard, audiology calibration.