ISO 389-7:2019

Overview

ISO 389-7:2019 - "Acoustics - Reference zero for the calibration of audiometric equipment - Part 7" - defines the reference threshold of hearing for calibrating audiometric equipment used in sound-field audiometry. It covers two listening environments: free-field (frontal incidence, free progressive plane wave) and diffuse-field (one-third-octave noise bands). The standard provides numerical threshold data for binaural listening across preferred one‑third‑octave frequencies from 20 Hz to 16 000 Hz, with additional intermediate audiometric frequencies up to 18 000 Hz.

Key Topics

• Scope of calibration: Applies when the sound field in the absence of the listener is either a free progressive plane wave or a diffuse sound field (as per ISO 8253‑2).
• Signal types:
  • Free-field: pure (sinusoidal) tones.
  • Diffuse-field: one‑third‑octave bands of white or pink noise.
• Measurement location: Sound pressure levels are measured at the position where the centre of the listener’s head would be, with the listener absent.
• Listening mode: Binaural only (median thresholds for otologically normal persons aged 18–25).
• Frequency coverage: Preferred one‑third‑octave series from 20 Hz to 16 000 Hz, plus some frequencies up to 18 000 Hz.
• Data derivation: Thresholds and diffuse/free-field differences are based on aggregated experimental data; Annex A documents the derivation and sources.
• Non‑comparability note: Thresholds differ from earphone/coupler‑based audiometric zero values in ISO 389‑1, ‑2, ‑5 and ‑8 (those are monaural, earphone‑based references).

Applications

ISO 389-7 is used to ensure accurate calibration of sound‑field audiometers and loudspeaker‑based audiometric setups in:

• Clinical audiology and diagnostic hearing clinics using speaker presentation.
• Occupational hearing conservation programs performing field or booth‑based sound‑field testing.
• Calibration laboratories and manufacturers of audiometric equipment and loudspeakers.
• Hearing research where standardized reference thresholds under free‑field or diffuse‑field conditions are required.
• Acoustic consultants setting up test rooms (free vs diffuse field) and verifying measurement positions.

Using ISO 389-7 helps maintain consistent, traceable audiometric calibration, improves comparability of sound-field test results, and supports regulatory and clinical quality assurance.

Related Standards

• ISO 8253‑1, ISO 8253‑2 - audiometric test methods and sound‑field specifications.
• ISO 226 - equal‑loudness and related free-field data (used in derivation).
• Other parts of ISO 389 (e.g., ISO 389‑1, ‑2, ‑5, ‑8) - earphone/coupler based audiometric zero references (monaural).

Keywords: ISO 389-7, reference threshold of hearing, audiometric equipment calibration, free-field, diffuse-field, sound field audiometry, binaural calibration, audiometric standards.