Improved measurement procedures for engine noise reduction with advanced microphones 2019-01-1463

Introducing a new transducer concept has resulted in considerable reduction in setup time and at the same time improved accuracy and repeatability for engine bay noise transfer studies. The acoustic environment inside cars are one of the primary comfort parameters. This is made up of a number of contributions from drivetrain, auxiliary equipment, wind noise and tire noise, and all are influenced by the transfer from the source to the receiver. With the change from purely internal combustion engines to electrical or electrical assisted propulsion systems, a new set of noise sources are introduced in the engine compartment and this requires renewed focus on the transmission paths to the receivers inside the car cabin. Typically, one of the tools to study these mechanisms is by using a reverse transmission technique, placing a well-defined sound source in the receiver position inside the car and measure the resulting sound pressure levels in the engine compartment. Assuming reciprocity, these measurements can be used to estimate the attenuation of transmission from sound sources in the engine compartment to the receiver inside the car. These measurements are time consuming and cumbersome as they involve the placement of up to 20 or more microphones in the engine bay. This has traditionally been performed using of-the-shelf measurement microphones. In order to optimize this procedure a new pressure field microphone has been introduced and tested by Volvo Car. The result has been a dramatic reduction in setup time, thereby enabling more configurations to be tested within the available time. At the same time a new mounting method has increased the accuracy repeatability and made it possible to maintain the same baseline throughout a complete project cycle.