ISO 9645:1990

Overview

ISO 9645:1990 provides an engineering method for measuring noise emitted by two-wheeled mopeds in motion. The standard is intended to deliver objective, reproducible acoustic results suitable for type approval, production checks and official test stations. It defines site conditions, instrumentation, operating conditions and reporting requirements to ensure consistent measurement of moped noise.

Key takeaways: A‑weighted sound levels, Class 1 instrumentation, calibrated equipment, controlled test site and repeatable vehicle operating procedures.

Key Topics

• Instrumentation and calibration

  • Use a Class 1 sound level meter (per IEC 651) or equivalent.
  • Measurements with frequency weighting A and time weighting F.
  • Instrument calibration must be checked before and after tests; record deviations. If the calibration shift exceeds 1 dB during a series, the series is invalid.

• Test site and environmental limits

  • Test site must be essentially horizontal and dry, with the test track and the 10 m radius around the centre formed of hard surface (concrete, asphalt or equivalent).
  • Within a 50 m radius of the track centre there should be no large reflective objects (buildings, bridges, rocks, fences).
  • Wind: measurements with mean wind speed at the microphone exceeding 5 m/s are invalid.
  • Background noise (including wind noise) must be at least 10 dB below the noise produced by the moped under test.

• Microphone position and geometry

  • Microphone height: 1.2 m ± 0.1 m above ground.
  • Distance from microphone to the reference line on the track: 7.5 m ± 0.2 m.
  • Microphone axis should be horizontal and perpendicular to the moped path.

• Measurement procedure and validity

  • At least three valid passes on each side of the moped are required.
  • Record the maximum A‑weighted sound pressure level (with F weighting) during each pass between defined track lines.
  • Results for a side are valid if the difference between extreme values of three consecutive valid measurements does not exceed 2 dB.
  • The test result is the higher of the two arithmetic means (one per side), rounded to the nearest 0.5 dB.

• Vehicle preparation and operating conditions

  • Moped must be in running order with recommended fuel, spark plug(s) and carburetor settings.
  • Total test mass (rider, test equipment and ballast) is specified in the standard (example range given in the text: 70–80 kg).
  • Tyres must be of the type normally fitted and inflated to the manufacturer’s recommended pressure.

Applications

• Type approval testing for manufacturers and regulatory bodies
• Production-line verification and factory conformance checks
• Accredited laboratory or official station acoustic evaluations

Related Standards

• ISO 4164 (vehicle engine power test code) - referenced for engine power-related data
• ISO 6726 (vocabulary for mopeds and motorcycles)
• IEC 651 (sound level meters) - instrument class and performance

Reporting and Practical Value

The test report must document site and weather conditions, equipment identification and calibration values, background noise level, vehicle and transmission identification, engine speed data, number and values of A‑weighted readings, and the declared test result. Following ISO 9645:1990 helps ensure repeatable, comparable moped noise data for compliance, development and research purposes.