ISO 11904-2:2021

Overview

ISO 11904-2:2021 - Acoustics: Determination of sound immission from sound sources placed close to the ear - Part 2: Technique using a manikin describes a standardized method to measure sound exposure from sources positioned near the ear (e.g., earphones, headsets, communication-equipped hearing protectors). Measurements use a head-and-torso manikin with integrated ear simulators and microphones, converting measured values into free-field or diffuse-field related equivalent continuous A-weighted sound pressure levels (LFF,M,Aeq / LDF,M,Aeq). The standard applies in the frequency range 20 Hz to 10 kHz; for higher frequencies ISO 11904-1 is recommended.

Key Topics and Requirements

• Measurement principle: Record one-third-octave band levels at the manikin ear simulators, apply the manikin-specific free-field (ΔLFF,M,f) or diffuse-field (ΔLDF,M,f) corrections, then apply A-weighting and combine bands to obtain equivalent continuous A-weighted levels.
• Instrumentation: Use a manikin/head-and-torso simulator meeting the acoustic and ear-simulator requirements (referenced: ITU‑T P.58:2013). Ensure correct coupling of earphones or devices to the artificial pinna-imperfect coupling or pinna stiffness differences can significantly affect results.
• Calibration: Check microphone and system calibration; for example, couple a class 1 acoustic calibrator (IEC 60942) to the occluded ear simulator and verify levels (unweighted).
• Frequency range: Valid measurements 20 Hz–10 kHz; for >10 kHz prefer ISO 11904-1.
• Uncertainty and reporting: Annex A lists common uncertainty sources; Annex B gives an example uncertainty analysis. The test report shall document measurement conditions, calibration, corrections applied, and results as free-field or diffuse-field related A-weighted levels.

Applications

• Laboratory testing of headphones, earphones, headsets and hearing protectors with audio/communication features.
• Workplace noise assessments where sources are close to the ear (e.g., handheld tools, communication headsets).
• Product compliance, acoustic design validation, and comparative performance testing of personal audio and protective equipment.
• Scenarios combining close-to-ear sources with external sound fields.

Who should use this standard

• Acoustical engineers and test laboratories
• Occupational hygienists and health & safety professionals
• Manufacturers of audio products and hearing protection
• Certification bodies and standards committees

Related Standards

• ISO 11904-1 (MIRE technique - microphones in real ears)
• ITU‑T P.58:2013 (head and torso simulator requirements)
• IEC 61260 (filters) and IEC 61672-1 (sound level meter specifications)
• IEC 60942 (acoustic calibrators)

Keywords: ISO 11904-2:2021, acoustics, manikin technique, sound immission, ear simulators, A-weighted sound pressure level, free-field related, diffuse-field related, headphone testing, workplace noise.