Noise pollution from category L vehicles is a major challenge in both urban and rural areas. High sound pressure levels negatively influence human health and the environment. To address these concerns, the current type-approval tests for category L vehicles are being revised. However, in order to analyse the effectiveness of the type-approval tests and make recommendations, the LENS project is developing a prototype sensor system to record noise emissions and GPS data under real driving conditions. The aim is to identify critical driving patterns that lead to particularly high noise emissions. For the planned test campaign, 14 different L-category vehicles will be equipped with the sensor system.

The on-board system developed consists mainly of a microcontroller, a dedicated electromechanical microphone capturing the noise emission, and a GPS module that simultaneously records the position and speed of the vehicle. Both sets of data are stored on a microSD card for later analysis and evaluation. For ease of use, the on-board system simply needs to be switched on and starts recording data immediately. A specially designed housing protects the components from the environment and allows easy installation on different vehicle types.    

The sensor system has been verified by comparative measurements with a conventional measuring microphone of the highest accuracy class in a suitable acoustic measuring room, a semi-anechoic chamber. Any discrepancies that occur can be corrected using appropriate signal processing methods, so that the sensor system allows a qualitative comparison of different vehicles with regard to critical driving patterns under real driving conditions. In addition, preliminary tests with different microphone positions were carried out to determine the appropriate positioning of the sensor system. Several of the above-mentioned conventional microphones were mounted on the vehicle, at the front, rear, centre and side. Different driving manoeuvres were used to investigate the effects of asymmetric sound radiation.