ISO 13472-2:2025

Overview - ISO 13472-2:2025 (Spot method for reflective road surfaces)

ISO 13472-2:2025 specifies an in situ spot method to measure the sound absorption coefficient of road surfaces under normal incidence conditions. The standard covers one-third octave band measurements from 250 Hz to 1 600 Hz (extendable to 2 000 Hz if an 80 mm impedance tube is used instead of 100 mm). The method is designed for reflective, semi‑dense to dense road surfaces and uses an impedance tube and two‑microphone transfer‑function analysis derived from ISO 10534‑2 signal processing principles.

Key technical topics and requirements

• Frequency range and tube sizes: Valid one‑third octave bands 250 Hz–1 600 Hz (100 mm tube); upper limit 2 000 Hz if tube diameter reduced to 80 mm. Smaller tube reduces the area under test (~0.005–0.008 m²).
• Measurement principle: Impedance tube mounted on the surface; propagation from source to surface and back; transfer‑function based analysis between microphone positions.
• Signal processing & quality: Specifies FFT resolution, sampling and block length, and coherence requirements for reliable transfer‑function estimation. Alternative microphone arrangements and alternating transfer functions (Annex C) mitigate destructive interference at microphone positions.
• Calibration and references: System stabilization, calibration, and a reference measurement procedure are required. Thermometer and barometer data must be recorded for environmental correction.
• Limits and validity: Not reliable for surfaces with sound absorption > 0.15 (air leakage effects). Surfaces with α ≤ 0.10 are considered reflective.
• Reporting and uncertainty: Measurement uncertainty assessment, conformity checks, and a standardized test report format (Annex E) are required.

Practical applications and users

ISO 13472-2 is intended for practitioners who need precise, in situ normal‑incidence absorption data for low‑absorbing road surfaces:

• Acoustic consultants and researchers performing pavement acoustic characterization.
• Road authorities and pavement engineers verifying compliance with design specifications.
• Test track operators and vehicle/tyre approval bodies assessing surface properties per ISO 10844 and national type‑approval regulations.
• Laboratories comparing in situ results with impedance‑tube core measurements (ISO 10534 series) for quality control and material development.

Benefits include non‑destructive testing, suitability for small spot measurements, and compatibility with impedance‑tube laboratory methods for comparative assessment.

Related standards

• ISO 13472‑1 (extended surface method)
• ISO 10534‑1 / ISO 10534‑2 (impedance tube techniques)
• ISO 10844 (test tracks)
• ISO 354 (reverberation room; different measurement field)
• ISO/IEC Guide 98‑3 (uncertainty of measurement)
• ASTM E1050 (comparable impedance tube method)

Keywords: ISO 13472-2, sound absorption, road surfaces, in situ measurement, impedance tube, spot method, reflective surfaces, one-third octave.