Optimization of engine noise reduction measurement procedure

Abstract

A comfortable and quiet environment in the car cabin is a key component for the driving experience and safety. The noise generated in the cabin, from the engine compartment, can be transmitted both via air-borne or structure-borne paths. The engine noise reduction measurement technique (ENR), takes into consideration only the airborne sound. The measurement technique is used before and after placing absorbers in the engine compartment to compare the different transmitted levels. Therefore, it is fundamental to understand if the difference in the two results is due to the actual absorbers or because of the uncertainties in the measurement procedure. This Master thesis focuses on the robustness and precision of the method within the frequency range for internal combustion engines and Electric battery vehicles. The available equipment and a new prototype of rugged pressure microphones from G.R.A.S Sound and Vibration have been used. The smallest possible error within the method has been found to be equal to 1 dB and therefore also the precision of the method. The robustness of the method for Combustion engine vehicle and Electric vehicle has been investigated and a safe frequency range has been found to be from 400 Hz to 8 kHz. In addition, an optimized number of microphones and their optimal location has been recommended. According to the data and the analysis, the method can be considered robust within the safe frequency range. The procedure has also been improved, weighting less the positions of the volume source, close to the windows, in the car compartment.