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ISO 28961:2012 — Acoustics — Statistical distribution of hearing thresholds
Reference hearing threshold distributions for otologically normal persons aged 18-25 under free-field conditions | Audiological engineering guide
Introduction to ISO 28961
ISO 28961:2012 specifies the statistical distribution of hearing thresholds of otologically normal persons in the age range from 18 years to 25 years under free-field listening conditions. Developed by ISO/TC 43 (Acoustics), this standard provides essential reference data for audiology, hearing aid design, and audio equipment calibration.
The standard provides percentile distributions of hearing thresholds at various frequencies, enabling engineers to determine what proportion of the young normal-hearing population can hear sounds at specific levels.
Key Technical Requirements
Threshold Distribution Calculation
The standard defines separate calculation methods for frequencies below 10,000 Hz and at 10,000 Hz and above. The threshold distribution is expressed as percentiles representing the statistical distribution across the population.
| Frequency (Hz) | Median P50 (dB) | P10 (dB) | P90 (dB) |
|---|---|---|---|
| 125 | 0.0 | -4.0 | 5.0 |
| 250 | 0.0 | -3.5 | 4.5 |
| 500 | 0.0 | -3.0 | 4.0 |
| 1000 | 0.0 | -3.0 | 4.0 |
| 2000 | 0.0 | -3.5 | 5.0 |
| 4000 | 0.0 | -4.0 | 6.0 |
| 8000 | 0.0 | -5.0 | 8.0 |
| 10000 | 2.0 | -4.0 | 12.0 |
| 12500 | 5.0 | -2.0 | 18.0 |
| 16000 | 10.0 | 0.0 | 28.0 |
The data applies only to otologically normal persons aged 18-25 years. Hearing thresholds for other age groups or persons with hearing impairment will differ significantly.
Engineering Design Insights
The statistical distribution data in ISO 28961 is essential for designing audio equipment with appropriate output levels. For example, if a hearing aid needs to be audible to 90% of the target population, the engineer must ensure the output exceeds the P90 threshold at each frequency. Conversely, the P10 values define the lower boundary of normal hearing.
The standard provides numerical examples illustrating the percentile calculation procedure, making it practical for engineers to implement the distribution models in their design software. The free-field listening condition specification ensures the data is applicable to real-world listening scenarios without headphone or earphone transfer functions.
These hearing threshold distributions serve as the reference baseline for audiometric equipment calibration, hearing aid fitting algorithms, and audio product design.
Applications in Engineering
The data supports audiological diagnostics, hearing conservation programs, and consumer audio product development. Understanding the statistical distribution enables engineers to design products that accommodate the full range of normal hearing sensitivity.
Frequently Asked Questions
Q: What does “otologically normal” mean?
A: Individuals with no history of ear disease, no excessive noise exposure, normal otoscopic findings, and no known genetic hearing disorders.
A: Individuals with no history of ear disease, no excessive noise exposure, normal otoscopic findings, and no known genetic hearing disorders.
Q: Why is free-field listening specified?
A: Free-field conditions eliminate the individual transfer function variations introduced by headphones, providing a more fundamental measure of hearing sensitivity.
A: Free-field conditions eliminate the individual transfer function variations introduced by headphones, providing a more fundamental measure of hearing sensitivity.
Q: Can these distributions be used for hearing-impaired populations?
A: No, these are reference distributions for normal-hearing young adults. Hearing-impaired populations require different reference data.
A: No, these are reference distributions for normal-hearing young adults. Hearing-impaired populations require different reference data.
