EN ISO 26101-2:2024 PDF

Overview

EN ISO 26101-2:2024 (ISO 26101-2:2024) specifies test methods to qualify an acoustic environment that approximates a free field near one or more reflecting planes. The primary aim is to determine the environmental correction (K) used to correct for reflected sound when calculating sound power level or sound energy level of machinery or equipment from sound pressure measurements taken on a surface that envelops the noise source. The standard is part of the ISO 26101 series and has been adopted by CEN as EN ISO 26101-2:2024.

Key topics and technical requirements

• Qualification procedures for environments approximating an acoustic free field, including general rules and accepted methods.
• Absolute comparison test - comparison of measured levels with a reference condition; locations for reference sources and required reporting.
• Room-absorption-based methods:
  • Reverberation method
  • Two-surface method
  • Direct determination of equivalent absorption area using a reference source
• Inverse-square-law qualification for specific measurement surface geometries (parallelepiped and cylindrical surfaces): criteria, allowable deviations from inverse-square behaviour, and maximum qualified volume.
• Test installation and procedures: requirements for test sound sources, source placement, microphone traverse paths, generation of sound, analysis bandwidth and spatial resolution of measurement points.
• Approximate method based on an estimated equivalent absorption area for simplified assessments.
• Reporting and documentation: mandatory information to record and report for reproducibility and compliance.
• Uncertainty: informative annex discussing uncertainty of the environmental correction.

Practical applications and users

• Used by acoustical engineers, accredited test laboratories, product manufacturers, and noise consultants to:
  • Verify suitability of a test room or site before conducting sound power or emission tests.
  • Calculate the environmental correction K to remove bias from reflected sound in measurements.
  • Ensure measurement comparability and conformity with referenced test standards.
• Frequently referenced by standards and test codes for product noise assessment (e.g., ISO 3744, ISO 3746, ISO 11201 family), where accurate sound power/energy values are required for regulatory compliance, product labeling, or R&D.

Related standards

• ISO 26101 series (other parts for environmental qualification)
• Sound power and emission standards such as ISO 3744, ISO 3746, ISO 11201, ISO 11202, ISO 11204
• CEN-adopted versions: EN ISO 26101-2:2024

This standard helps ensure reliable, reproducible sound power and sound energy measurements by formally qualifying the test environment and quantifying the environmental correction used to compensate for reflected sound.