ISO 13472-2:2010

Overview

ISO 13472-2:2010 - "Acoustics - Measurement of sound absorption properties of road surfaces in situ - Part 2: Spot method for reflective surfaces" - specifies a portable in‑situ test method for determining the normal-incidence sound absorption coefficient of road surfaces. The method adapts the two‑microphone impedance tube (transfer‑function) technique to a small, fieldable apparatus to measure one‑third‑octave bands from 250 Hz to 1 600 Hz (modifiable for special purposes). It is optimized for reflective, low‑absorption road surfaces such as those used on test tracks and in vehicle/tyre type‑approval tests.

Key Topics and Technical Requirements

• Frequency range: One‑third‑octave bands with centre frequencies from 250 Hz to 1 600 Hz (narrowband equivalent ~220 Hz–1 800 Hz).
• Measurement principle: Two‑microphone impedance tube (transfer‑function method) following ISO 10534-2 / ASTM E1050 signal-processing to compute the complex reflection factor and absorption coefficient under normal incidence.
• Apparatus components: Signal generator, loudspeaker, impedance tube (~0.008 m2 opening), two flush‑mounted microphones, in‑situ test fixture with airtight seal (deformable ring/O‑ring), analyzer/processing unit, thermometer and pressure measurement.
• Calibration & verification: Verification of microphone amplitude/phase relationship and determination of internal energy loss using a totally reflecting reference measurement. Routine checks include reference and background noise measurements.
• Limitations: Designed for semi‑dense to dense (low‑absorption) surfaces; method is not reliable if absorption coefficient exceeds 0.15 (values >0.10 indicate non‑reflective behavior).
• Data quality: Guidance on measurement uncertainty, positioning, environmental conditions (temperature, surface condition), and detailed test reporting requirements are included.

Practical Applications and Users

ISO 13472-2 is intended for:

• Acoustic engineers and test laboratories performing in‑situ sound absorption measurements.
• Vehicle and tyre manufacturers and certification bodies verifying test tracks and surfaces to standards such as ISO 10844.
• Road authorities, pavement designers, and contractors for quality control, design verification, and maintenance monitoring of road surfacings.
• Researchers and consultants conducting traffic‑noise studies where normal‑incidence absorption data are required.

Benefits include non‑destructive, rapid field measurement that produces results comparable to lab impedance‑tube tests on bore cores (within the method’s valid range).

Related Standards

• ISO 10534-2: Transfer‑function impedance tube method (signal processing basis)
• ISO 13472-1: Extended surface method (complementary, larger area, wider frequency range)
• ISO 10844: Test track specification for vehicle/tyre noise testing
• ASTM E1050, ISO 354, IEC 61260, ISO/IEC Guide 98-3 (uncertainty guidance)

Keywords: ISO 13472-2, acoustics, sound absorption, road surfaces, in situ measurement, spot method, reflective surfaces, impedance tube, normal incidence, ISO 10844, vehicle noise testing, tyre test tracks.