This presentation is intended to illustrate the differences between both the proposed VOLPE/NHTSA test method and the current ISO 16254/SAE J2889-1 in terms of vehicle test conditions, measurements and information metrics, indoor and component testing and pitch shifting. For this purpose, 4 work packages for data collection were developed:

1: Measurement of vehicles at the conditions outlined by NHTSA/Volpe in the published research report. Measurements include both Indoor and Outdoor evaluations. Data collected to date: Background noise evaluations, vehicle measurements

2: Measurement of interior sound (recordings and analysis), Evaluation of transmission loss. Data collected to date: Recordings available, Transmission Loss evaluated.

3: Correlation of detection and recognition to proposed levels. Data collected to date: Jury evaluations of detection and recognition.

4: Measurement of frequency shifting at conditions outlined in NHTSA/VOLPE research report. Data collected to date: Indoor and outdoor evaluations.

The use of 1/3 octaves for the sole performance specification as proposed in the NHTSA/VOLPE research paper will require changes to the ISO/SAE test procedures to provide for the sound being measured to be available for a time of approximately 30 seconds. Correction of 1/3 octaves with background noise levels is not possible due to variation.

The test methods proved to be sensible against background noise so that indoor testing appears more promising in view of repeatable and reproducible results. This avoids the necessity for outdoor test facilities in extremely low noise areas as ‘2m’ indoor-facilities with cut off frequencies below 200Hz are widely available.

Canada was not aware of any indoor facilities available, Spain mentioned that there is no standard available for the certification of indoor labs, OICA replied that indoor facilities are used today for horn (ECE R28) certification and that many anechoic test benches exist that would satisfy the necessary cut-off frequency for testing. In addition ISO is working on a standard for indoor type approval for the purpose of pass-by noise certification. Japan knows about suitable test facilities, which however are barely available for governments. ISO informed that most OEMs had indoor facilities available and that the ISO/SAE procedure was written so to be applied in- and outdoor.

Measurement of pitch shift will need to be accomplished at a component level, or on a vehicle in such a manner as to simulate a component test, and utilizing narrowband analysis for technically correct measurements. Knowledge of the signal used is required for correct testing.