When a car drives past you on the street and you hear the engine roar, the turbo whirring, or the rolling of the wheels on the road – all of those sounds emanating from the vehicle must be controlled through a rigorous measurement process before the car is legally allowed to circulate. This is the scope of ISO 362 – the international standard for measuring vehicle noise during acceleration, also known as pass-by noise testing.
What is ISO 362?
ISO 362, whose full name is Acoustics - Measurement of noise emitted by accelerating road vehicles - Engineering method, is an international standard issued by ISO that specifies a method for measuring the noise level emitted by a vehicle under typical urban operating conditions (acceleration, steady speed). It serves the purpose of traffic noise control and vehicle type approval certification.
This set of standards comprises several parts applicable to different vehicle categories:
- ISO 362-1: Applies to vehicles of types M and N (passenger and cargo vehicles), measured outdoors on a test track. Two-wheeled and three-wheeled vehicles of types L1 and L2 are specified separately in ISO 9645, while L3, L4, and L5 are covered by ISO 362-2.
- ISO 362-3: Specifies an equivalent measurement method performed in a semi-anechoic chamber equipped with a dynamometer, replacing the outdoor measurement method - allowing for indoor testing, independent of weather conditions.
Why is standardization of vehicle noise measurement necessary?
Urban traffic noise is one of the biggest sources of noise pollution in cities, directly affecting the health and quality of life of residents. Without a standardized measurement method, each vehicle manufacturer or each country may apply different measurement techniques, leading to incomparable results and making it impossible to establish legal noise limits.
ISO 362 addresses this issue by precisely specifying: test track conditions, microphone placement, vehicle speed and operating procedures during measurement, and the formula for calculating the final noise level (Lurban). This allows measurement results from a lab in Asia to be directly compared with results from Europe or North America, forming the basis for global regulations limiting vehicle noise levels – for example, Canada directly applies ISO 362-1:2015 with limits of 78 dBA for passenger cars and 80 dBA for light trucks in its motor vehicle safety regulations.
The main technical requirements of ISO 362-1
Standard test track
The test track must be level, the surface must comply with the requirements of ISO 10844 (standardized road surface type for noise measurement), and the space within a 50 m radius around the center of the measurement area must be free of large sound-reflecting objects such as walls, rocks, bridges, or construction works.
Arrange measurement points AA', BB', PP'
The standard defines the reference points on the test track as follows: point AA' is the position where the vehicle begins to accelerate to its maximum speed, point BB' is the position where the vehicle finishes accelerating and returns to the normal throttle position, and point PP' is located between AA' and BB' - this is the position of the measuring microphone, 7.5 m from the center of the test track. The lengths of the test track l10 = 10 m and l20 = 20 m are used to calculate the actual acceleration of the vehicle during the measurement process.
Vehicle speed and operating conditions during measurement.
The vehicle approaches the measurement area at a constant speed (typically 50 km/h for vehicles with a power-to-weight ratio (PMR) above 50, or 40 km/h for vehicles with a lower PMR), then accelerates to full speed upon reaching point AA' and maintains this speed until point BB'. The measurement is repeated several times in different gear ratios (e.g., gears 2 and 3), and the peak value of the A-weighted negative pressure level is recorded.
Lurban urban noise level calculation formula
The final result is calculated using a formula that combines noise levels measured at maximum acceleration and noise levels measured at steady speed, most accurately reflecting the actual noise emitted by the vehicle in everyday urban traffic conditions – this is the value Lurban uses to compare against legal limits.
The significance of ISO 362 in NVH testing.
Legal basis for vehicle type approval
ISO 362 measurement results are a mandatory requirement for a vehicle to be licensed for circulation in many countries and regions. With a phased approach to tightening noise limits (for example, applying in 2016, 2020, and 2024 for newly launched vehicles, and 2018, 2022, and 2026 for vehicles currently in production), manufacturers must integrate ISO 362 testing into their product development processes very early on to ensure compliance with increasingly stringent limits – potentially reducing noise levels by up to 6 dBA compared to previous levels for passenger cars.
Noise reduction design guidelines from the development stage.
Because Lurban measurements reflect the combined noise from the engine, exhaust system, tires, and aerodynamics, the ISO 362 test forces manufacturers to optimize multiple NVH sources simultaneously, not just interior cabin noise but also noise emanating from outside the vehicle.
Connecting outdoor and indoor testing.
The existence of ISO 362-3, with its semi-sonic chamber measurement method combined with a dynamic test bench, allows NVH laboratories to perform measurements equivalent to ISO 362-1 regardless of weather conditions or the history of outdoor test track use. This is one of the reasons many manufacturers choose to invest in semi-sonic chamber systems integrated with dynamic test benches right at their R&D facilities, to be more proactive in the testing and development process.
Comparison of ISO 362-1 and ISO 362-3
|
Criteria |
ISO 362-1 (outdoor) |
ISO 362-3 (indoor) |
|
Measurement environment |
Outdoor test track according to ISO 10844 |
The semi-non-sonic chamber has a dynamic test bench. |
|
Weather dependent |
Yes - suitable wind, temperature, and humidity conditions are required. |
No - complete indoor control |
|
Main equipment |
Outdoor measuring microphone, vehicle speed/acceleration measurement system. |
Dynamic test bench, in-chamber microphone, synchronized data acquisition system. |
|
Application |
Official type approval |
Repeated R&D testing, rapid testing in product development. |
|
Repeatability |
Affected by environmental conditions each time a measurement is taken. |
Higher due to a stable, controlled environment. |
GPower Vietnam - a vehicle noise measurement solution compliant with ISO 362.
GPower Vietnam provides consulting and integration services for vehicle noise measurement system components tailored to testing requirements, from measuring equipment to data acquisition and processing systems.
Items may include:
- Laboratory construction consultancy: Design of a semi-attenuated chamber with integrated dynamic testing platform , meeting indoor measurement method requirements according to ISO 362-3.
- Supplier consultation: Connect with reputable measurement equipment brands such as Kistler, GRAS, HEAD acoustics, and select a dynamic test bench suitable for your testing requirements.
- Integrated solution consulting: Ensuring that the vehicle speed and acceleration measurement system and measuring microphones operate synchronously according to the technical procedures of the standard.
- Calibration, warranty, and maintenance: Maintaining the accuracy of the entire measurement system over time, ensuring the repeatability of test results.
Contact GPower Vietnam today for advice on the most suitable ISO 362 vehicle noise measurement solution for your project - Hotline: 0936093289 | Email: info@gpower.com.vn.
Refer to the articles on standards used in NVH testing:
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