THE BACK PAGE


Acoustic Sensors Toughen Up


Car makers step in to help develop NVH assessment equipment that’s tough enough for the job.


N


oise, Vibration and Harshness (NVH) represents such a key issue for the new wave of passenger cars that are being developed, that Volvo and Volkswagen have become involved in the development of test equipment that can stand up to the harsh environments in which it’s expected to operate.


The noise profile of hybrid and fully electric vehicles is entirely different to vehicles of old and the sources of NVH have changed so manufacturers have to dig deeper and listen more carefully. To do this, the two automotive giants have been working with GRAS Sound and


Vibration on equipment development, the results of which are the 147AX CCP Rugged Pressure Microphone for engine noise testing and the 147EB CCP Extra- rugged Microphone for brake noise testing.


ENGINE NOISE REDUCTION


According to GRAS, engine noise reduction incudes Acoustic Transfer Function (ATF) determination. The reciprocity method is used for this with a high number of free-field microphones but it is cumbersome and very time consuming. Because set up is difficult to reproduce, the accuracy of the results is limited. To overcome this, the 147AX CCP Rugged Pressure Microphone was developed in conjunction with Volvo Cars in Sweden. It is a surface microphone optimised for highly efficient cold and hot engine noise testing and repeatable measurements. Plus, it introduces a revolutionary form factor, which together with a unique mounting system and new measurement methods, ensures accurate and reliable data.


BRAKE NOISE REDUCTION Due to the rough environment, recording of brake noise in the wheelhouse during road testing is very demanding. This generally leads to the use of sub-standard microphones with limited or even unknown acoustic performance. As a result, it often requires custom-made and troublesome protection of the microphone The new 147EB CCP Extra-Rugged Microphone Set is an extremely robust microphone which has been specially designed and optimised for on-road brake noise testing. The microphone has three-layer protection of the diaphragm and has been tested with Volkswagen in Germany where it has undergone more than 10,000 miles of on-road testing on all surfaces and in all weather conditions. GRAS Product Manager Jan Hansen comments: “GRAS has developed new products targeted at specific applications that revolutionise existing test methods and significantly reduce rigging up time. We have tried to address the most common challenges as experienced by industry professionals within each application area by way of mapping these from start to finish.”


❱ ❱ A new generation of automotive NVH assessment microphones is providing high accuracy measurements in harsh environments


20 /// Climatic & Vibration Testing Vol 2 No. 2


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