automotive_passbynoise.jpg

Pass-by noise

The environmental noise pollution must be minimized to ensure people’s health and comfort. Traffic noise is for this reason regulated and without fulfilling the regional targets for pass-by noise, a vehicle model cannot get a type approval and be put on the market. The international test methods have been developed to capture realistic driving conditions even better and the noise level limits are reduced. This puts obviously a lot of focus on vehicle development and also robustness in production. The methods for measuring pass-by requires a lot of dedicated facilities like specialized test tracks, large indoor NVH chassis dyno test cells and high performance test equipment to produce comparable measurement results. Before running verification tests, thorough investigations of the most contributing sources (engine and intake/exhaust system, tyre noise) are done to predict the total noise level.

Electrical vehicles on the other hand may be too silent in city driving. This may be a risk for pedestrians used to be able to hear an approaching vehicle or for persons with impaired vision. New regulations are under introduction for AVAS, Acoustic Vehicle Alert Systems and these must also be verified.

Challenges:
Indoor tests and predictions are getting more and more important to be able to fulfil legislation within tight planned vehicle development projects. Indoor testing methods requires a microphone array on each side of the vehicle in a NVH semi-anechoic chassis dyno test cell to simulate the pass-by noise driving Tyre noise will also be more important for future vehicles and especially for electrical vehicles.

Other testing concerns the AVAS systems in electrical vehicles which must not only be fulfilling target sound levels but needs also sound quality design. Branding and a new type of noise pollution in cities must be considered.
Finally, all outdoor equipment must be either weather proof or easy to install/remove and also fulfil the testing standards.

Example:
Pass-by testing includes acceleration tests, constant speed tests and static tests for a stand still vehicle on a dedicated test track. Systems for logging vehicle speed and weather conditions during the measurement are compulsory.
The tests can also be performed indoor by the use of microphone arrays on each side of the vehicle simulating the pass-by driving. This is effective for running tests without being dependent of the weather and also for advanced development testing. The microphones and measurement equipment must be calibrated according to regulations.

The microphones must fulfil the test procedures, typically a class 1 free-field microphone. Outdoor microphones with weather protection and internal heating are preferred for permanent installations.