Acoustics - Reference zero for the calibration of audiometric equipment - Part 1: Reference equivalent threshold sound pressure levels for pure tones and supra-aural earphones
1Key Takeaways
This document specifies a standard reference zero for the scale of hearing threshold level applicable to pure-tone air conduction audiometers, to promote agreement and uniformity in the expression of hearing threshold level measurements throughout the world. It states the information in a form suitable for direct appli…
2Expert Interpretation
An in-depth interpretation of the ISO 389-1:2017 international standard, covering the technical requirements for the Reference Equivalent Threshold Sound Pressure Level (RETSPL) for the calibration of pure-tone audiometry equipment, including calibration data for general-purpose and specific headphone models, and the application specifications and implementation recommendations for the IEC 60318 series of simulators.
Analysis of the core content of the standard
The ISO 389-1:2017 standard specifies the reference zero level for the calibration of pure-tone air conduction audiometers. By defining the equivalent threshold sound pressure level (RETSPL) of over-ear headphones at different frequencies, it ensures the consistency of global hearing threshold measurements. The main technical updates include:
| Key Elements | 1998 Edition | Major Changes from the 2017 Edition |
|---|---|---|
| Headphone Model Coverage | Basic Models | Added 5 new models including Sennheiser HDA 280 |
| Simulator Standards | IEC 60318-1:1998 | Synchronized Update to IEC 60318-1:2009 Requirements |
| Data Accuracy | ±1dB | ±0.5dB (Improved Static Force Control) |
Key Points of Technical Implementation
1. Equipment Coupling Specifications
The standard specifies coupling requirements for three calibration scenarios:
- General-purpose headphones: Must meet 8 geometric and acoustic characteristic requirements (Clause 4.2)
- IEC 60318-1 Ear Simulator: Axial vertical alignment, static force 4.5N±0.5N
- IEC 60318-3 Acoustic Coupler: Specific models require an adapter (such as Beyer DT 48)
2. Key Data Comparison
| Frequency (Hz) | General RETSPL (dB) | HDA 280 difference value |
|---|---|---|
| 1000 | 7.5 | -1.5 |
| 6000 | 15.5 | +3.0 |
Background of Standard Evolution
Data from a joint study conducted by five major national laboratories (PTB, NPL, etc.) from 1950 to 2010:
- Basic Data: Average of 15 sets of historical measurements of Beyer DT 48
- Interpolation Method: Cubic polynomial in the 125-1000Hz range, linear interpolation in the high frequency band
- New verification: Headphones added after 2010 must be verified under the ISO 389-9 preferred test conditions
Application Case: Hospital Audiometer Calibration
When a tertiary hospital uses Telephonics TDH 39 headphones:
- MX41/AR earpads must be used
- Couple selection has a significant impact: at 1kHz, IEC 60318-3 is 2.5dB higher than IEC 60318-1
- Headband pressure must be strictly controlled at 4.5N±0.5N
Implementation Recommendations
Priority level:
- Preferred model-specific data (clauses 4.3/4.4)
- Secondary general data (must fully comply with the 8 requirements of 4.2)
- Non-standard headphones need to be re-measured according to ISO 389-9
Quality control: Regularly verify headband pressure (4.5N for 145mm head width) and earpad sealing