ISO 12999-2:2020

Overview

ISO 12999-2:2020 - Acoustics: Determination and application of measurement uncertainties in building acoustics - Part 2: Sound absorption - provides a practical, standardized method to quantify and report the measurement uncertainty associated with sound absorption data. It covers uncertainties for laboratory measurements and derived single-number ratings so that designers, test labs and specifiers can present absorption data with transparent confidence intervals.

Key topics

• Scope: procedures for calculating uncertainties of:
  • Sound absorption coefficients and equivalent absorption areas measured to ISO 354.
  • Practical and weighted sound absorption coefficients per ISO 11654.
  • Object sound absorption coefficient per ISO 20189.
  • Single-number rating per EN 1793-1.
• General approach:
  • Uses reproducibility and repeatability concepts (inter‑laboratory and within‑lab variability) rather than full analytical models.
  • Recommends using available inter-laboratory data where possible.
• Technical content provided:
  • Frequency-dependent formulas and tabulated constants for calculating standard uncertainties in one‑third octave bands.
  • Rules for converting standard uncertainties to expanded uncertainty using a coverage factor k (e.g., k ≈ 2 for ~95% confidence).
  • Rounding and reporting conventions (digits and presentation examples).
• Examples: illustrative results for one‑third octave band absorption, weighted coefficients and single‑number values (e.g., αw = 0.70 ± 0.07, k = 2).

Applications and users

• Who uses it:
  • Accredited acoustic laboratories and test houses conducting ISO 354 measurements.
  • Acoustic consultants and specifiers documenting material or element absorption performance.
  • Manufacturers of acoustic materials (ceilings, insulation, sound absorbers) preparing datasheets.
  • Certification bodies and compliance assessors comparing test data and declaring ratings.
  • Researchers and inter-laboratory study organizers evaluating method repeatability/reproducibility.
• Practical benefits:
  • Enables consistent, comparable reporting of absorption data with quantified confidence.
  • Supports product selection, acoustic design, and regulatory compliance by making uncertainties explicit.
  • Facilitates interpretation of single-number ratings in noise control and road/rail applications (EN 1793-1).

Related standards

• ISO 354 - Measurement of sound absorption in a reverberation room
• ISO 11654 - Rating of sound absorption
• ISO 20189 - Object sound absorption coefficient
• EN 1793-1 - Single-number ratings for road traffic noise barriers
• ISO/IEC Guide 98-3 (GUM) and ISO 5725 - uncertainty and reproducibility/repeatability guidance

Keywords: ISO 12999-2:2020, sound absorption, measurement uncertainties, ISO 354, ISO 11654, ISO 20189, EN 1793-1, building acoustics, reproducibility, repeatability, uncertainty reporting.