ISO 28961:2012

Overview

ISO 28961:2012 specifies the statistical distribution (percentiles) of hearing thresholds for otologically normal persons aged 18–25 years measured under defined free‑field listening conditions. The standard provides descriptive statistics that reference the median thresholds given in ISO 226 and ISO 389‑7, and supplies methods and tabulated percentiles for one‑third‑octave and selected audiometric frequencies from 20 Hz to 16 000 Hz.

Key topics and requirements

• Defined measurement conditions:
  • Free progressive plane wave (free field)
  • Sound source directly in front (frontal incidence)
  • Pure (sinusoidal) tones, binaural listening
  • Sound pressure measured at the centre of the listener’s head (absence of listener)
  • Listeners otologically normal, ages 18–25 inclusive
• Statistical approach:
  • For frequencies < 10 000 Hz: threshold distributions are approximated by a Gaussian distribution; percentiles are computed from the mean (set equal to ISO 226 / ISO 389‑7 reference thresholds) and frequency‑dependent standard deviations (Table 1).
  • For frequencies ≥ 10 000 Hz: thresholds are power‑transformed to achieve approximate normality, then percentiles are calculated in the transformed domain and inverse‑transformed back to dB (parameters provided in Table 2).
  • Standard z‑scores for percentiles are provided (Annex C) and numerical examples are included (Annex A).
• Output:
  • Numeric percentiles (e.g., 1, 5, 10, 25, 50, 75, 90, 95, 99) for preferred one‑third‑octave band center frequencies per ISO 266, and some intermediate audiometric frequencies (Annex B).

Practical applications and users

ISO 28961:2012 is used to:

• Assess an individual’s hearing relative to a well‑defined young‑adult population (clinical audiology, occupational health).
• Evaluate audibility of low‑level noise and estimate the proportion of young people likely to detect a sound source (environmental and product noise assessment).
• Support noise emission and acoustic product testing, and complement standards such as ISO 7779 for noise measurement and evaluation. Typical users:
• Audiologists and hearing clinicians
• Acoustic and noise consultants
• Product designers and manufacturers concerned with sound emissions
• Occupational health and safety professionals
• Researchers in psychoacoustics and hearing science

Related standards

• ISO 226:2003 - Normal equal‑loudness‑level contours (reference thresholds)
• ISO 389‑7:2005 - Reference zero for audiometric calibration (free‑ and diffuse‑field thresholds)
• ISO 266 - Preferred frequencies (one‑third‑octave series)
• ISO 7779 - Measurement of airborne noise emitted by information technology and telecommunications equipment (referenced application)

ISO 28961:2012 provides the statistical framework needed to interpret young‑adult hearing thresholds, supporting clinical assessment, noise audibility studies, and standardized acoustic evaluations.