ISO 4869-3:2007

Overview - ISO 4869-3:2007 (Acoustics, ear-muff insertion loss)

ISO 4869-3:2007 specifies a laboratory method to measure the insertion loss of ear-muff type hearing protectors using an acoustic test fixture (ATF). The standard defines the ATF geometry, microphone requirements, test-site sound fields, measurement signals and procedures to obtain one‑third‑octave‑band insertion‑loss data (typically 63 Hz to 8 kHz). It is intended for production‑spread investigations, ageing studies and to verify that samples submitted for subjective attenuation testing (ISO 4869‑1) are representative of the type. It is explicitly not the basic test for type approval and does not replace real‑ear attenuation measurements.

Key topics and technical requirements

• Measurement principle: insertion loss = difference (dB) between ATF microphone levels with and without the ear‑muff fitted.
• Acoustic Test Fixture (ATF): cylindrical fixture, centre‑to‑centre end faces (145 ± 1) mm, diameter (135 ± 5) mm; microphone axis and diaphragm positioned at the end face; resilient mounting to reduce structure‑borne noise.
• Microphone: pressure‑operated condenser types WS1P or WS2P per IEC 61094‑4.
• Spacer and headband support: spacer length (123 ± 1) mm with rubber pad (6 ± 1 mm), pad hardness 30–85 IRHD (ISO 48).
• Acoustic isolation: minimum isolation at the test site - 50 dB (63–250 Hz), 65 dB (315 Hz–4 kHz), 55 dB (higher bands) using an isolation test cup.
• Test signals and analysis: pink noise, MLS, impulse‑response, etc.; results reported in one‑third‑octave bands per IEC 61260; required signal‑to‑noise ratio ≥ 10 dB and stable test level (±1 dB).
• Test procedure: measure without ear‑muff, fit ear‑muff per positioning rules, wait ~30 s, measure with ear‑muff; compute insertion loss per band.
• Limitations: data from ISO 4869‑3 are not direct substitutes for real‑ear attenuation or the protection provided in use.

Applications and users

Who uses ISO 4869‑3:

• Test laboratories performing production quality checks and repeatability/ageing studies of ear‑muffs.
• Manufacturers verifying representative samples for subjective testing (ISO 4869‑1).
• Certification bodies and R&D teams comparing design variants, cushions or headband effects in controlled conditions.
  Practical benefits:
• Reproducible laboratory comparison of ear‑muff performance.
• Identification of production variability and performance degradation over time.
• Support for product development and internal quality control.

Related standards

• ISO 4869‑1 - Subjective method for sound attenuation
• ISO 4869 (other parts) - Estimation and level‑dependent measurements
• IEC 61094‑4 - Measurement microphone specifications
• IEC 61260 - One‑third‑octave filters
• ISO 48 - Rubber hardness (IRHD)
• ISO/IEC Guide 98 (GUM) - Uncertainty of measurement

Keywords: ISO 4869-3, acoustic test fixture, insertion loss, ear‑muff, hearing protectors, measurement method, acoustics standard, test laboratory, one‑third‑octave.