ISO 26101-2:2024

Overview - ISO 26101-2:2024 (Acoustics, Environmental Correction K2)

ISO 26101-2:2024 specifies test methods to qualify an acoustic environment that approximates a free field near one or more reflecting planes. Its primary objective is to determine the environmental correction K2, a frequency‑dependent correction applied to sound pressure measurements on a measurement surface to account for reflected sound. K2 is used when deriving sound power levels or sound energy levels of machinery and equipment from surface sound pressure measurements.

Key topics and technical requirements

• Definition and purpose of K2: Explains how K2 corrects the mean (energy average) sound pressure over microphone positions and how it depends on measurement surface shape and size.
• Four qualification procedures (Clauses 4.2–4.5):
  • Absolute comparison test using a reference sound source (preferred for band‑by‑band data; see Clause 5).
  • Room absorption methods including the reverberation method and two‑surface method (Clause 6).
  • Inverse‑square‑law qualification for parallelepiped and cylindrical measurement surfaces, including installation, microphone traverses, and qualification criteria (Clause 7).
  • Approximate method based on estimating the equivalent absorption area (Clause 8).
• Test setup and reporting: Requirements for reference sound sources, source and microphone positioning, spatial sampling, analysis bandwidth, and the information to be recorded and reported for reproducible K2 determination.
• Uncertainty considerations: Annex A gives guidance on the uncertainty of the environmental correction, and the standard states that differences due to measurement‑surface variations are to be included in stated measurement uncertainty.
• Normative references: Links and cross‑references to ISO 3744, ISO 3745, ISO 6926 and ISO 26101‑1 for related measurement and reference source requirements.

Practical applications and users

• Acoustic test laboratories qualifying test rooms or outdoor sites before sound power/energy measurements.
• Manufacturers and test engineers who perform ISO 3744/3746 or emission sound pressure tests (e.g., ISO 11201, ISO 11202, ISO 11204) and need reliable environmental corrections.
• Certification bodies and acoustic consultants ensuring compliance with international measurement methods and reporting consistent K2 values.
• R&D and product compliance teams that require validated laboratory environments or documented corrections for regulatory or contractual claims.

Related standards

• ISO 3744:2024 (sound power, engineering methods)
• ISO 3745:2012 (precision methods for anechoic rooms)
• ISO 6926 (reference sound source requirements)
• ISO 26101-1 (qualification of free‑field environments)

Keywords: ISO 26101-2:2024, environmental correction K2, acoustics, sound power level, measurement surface, free field, reverberation, inverse-square-law, equivalent absorption area.