Overview
ISO 20908:2023 - Tyre sound emission test - Methods of drum specifies standardized methods for measuring tyre-to-road sound emissions using an indoor drum rig. The standard covers testing of passenger car and light commercial vehicle tyres under coast‑by (free‑rolling) conditions in a semi‑anechoic environment. Its objective is to deliver indoor measurements that correlate closely with outdoor exterior-noise type‑approval tests (see ISO 13325), enabling year‑round, weather‑independent tyre noise evaluation. This standard is not for tyres under applied torque or for locating traffic noise nuisance.
Key technical topics and requirements
ISO 20908 defines comprehensive technical and procedural requirements, including:
- Instrumentation and calibration
- Acoustical measurement instruments, microphone specifications and calibration, temperature measurement and conformity checks.
- Test room and acoustic environment
- Semi‑anechoic room criteria, background noise limits, far‑field validation and acoustical qualification to ensure sound behavior suitable for drum testing.
- Microphone array configurations
- Multiple setups (linear array, circular array, single‑microphone options) and validation of inverse‑square propagation conditions for simulated vehicle trajectories.
- Drum and tyre interface
- Requirements for the drum, drum surface, loading devices, tyre condition and tyre pressure measurement to emulate road contact comparable to ISO 10844 surfaces.
- Test procedures and data processing
- Tyre preparation (load, pressure, thermal conditioning), speed ranges, pre‑treatment of signals, normalization (distance, number of tyres, masking effects, speed), emulation of fast time weighting and reporting formats.
- Correlation, validation and uncertainty
- Procedures for correlation with outdoor ISO 13325 measurements, alignment coefficients, correction factors, stability checks and a framework for measurement uncertainty (referencing ISO/IEC Guide 98‑3).
Practical applications and users
ISO 20908 is practical for:
- Tyre manufacturers - design validation, noise reduction development and production verification.
- Independent test laboratories and certification bodies - repeatable indoor testing aligned with type‑approval benchmarks.
- Regulatory agencies and R&D organizations - method for comparing tyre acoustic performance without outdoor track constraints.
- OEMs and acoustic consultants - integration of tyre noise data into vehicle noise assessments and NVH programs.
Benefits include reproducible, weather‑independent data, reduced test variability across sites, and a standardized path to correlate indoor bench results with outdoor type‑approval outcomes.
Related standards
- ISO 13325 - Exterior noise measurement on test tracks (outdoor reference method).
- ISO 10844 - Road surface characteristics for tyre tests (surface emulation).
- ISO/IEC Guide 98‑3 - Guide to measurement uncertainty (referenced in Annex A).
Keywords: tyre sound emission, tyre noise testing, drum rig, semi‑anechoic chamber, microphone array, ISO 20908, ISO 13325, measurement uncertainty, tyre acoustic testing.