Case Study: NVH: Road Noise Development

Excessive levels of road related noise in a European specification C/D class saloon vehicle.  The brief for MIRA was to improve to road noise without compromising the handling performance of the vehicle.

A comprehensive benchmarking exercise included:

• Body sensitivity at the suspension-to-body connection points
• Vehicle configuration and acoustic treatment analysis
• K&C test rig data

The road noise issue was found to be in the 100 to 400 Hz band.  The second phase of the project was aimed at locating the source of the problem in terms of:

• Balance of front/rear axle contributions
• Balance of structure borne/airborne contributions

Through the use of road noise simulators, the significant contribution was found to be structure borne through paths associated with the rear axle.

Transfer path analysis was used to determine the source of the structural input from the rear suspension.  It was determined that the key inputs were through the solidly mounted rear subframe.

A combination of ADAMS modelling, subjective appraisals and objective measurements were used to design and fabricate an existing subframe to incorporate the appropriate isolation and body modifications for improved NVH performance.

Data showed a significant reduction in the road noise was achieved.  Handling subjective appraisals and K&C data from the modified vehicle proved that the handling performance was not compromised.

The project concluded with a demonstrator vehicle being presented to the customer at a drive appraisal.  The objectives in terms of noise reduction and handling performance were met to the satisfaction of the customer.