The acoustic environment inside the car is a primary comfort parameter. With the change from internal combustion engines (ICE) to electrical (BEV) or electrically assisted (HEV) propulsion systems, a renewed focus on old and new noise sources in the engine bay and the transmission paths to the cabin is required.
A way to study this is by using a reverse transmission technique, placing a sound source in the receiver position in the cabin and measure the resulting sound pressure levels in the engine bay. Assuming reciprocity, the attenuation of transmission from sound sources in the engine bay to the cabin can be estimated. These measurements are cumbersome as they involve the placement of 20 or more microphones in the engine bay. This has traditionally been performed using off-the-shelf free-field measurement microphones.
To optimize this procedure a new pressure-field microphone has been tested by Volvo Cars. The result has been a dramatic reduction in setup time; also, a new mounting method has increased accuracy and repeatability and made it possible to maintain the same baseline throughout a complete project cycle. In addition to this, hot engine and track testing is now possible using the same measurement setup.