Road test to analyze real life NVH

When a car is in use, there can be noise and vibrations that enter the cabin from the car engines/moving parts, road and the environment around the car. While too much noise can be distracting, too little removes a critical piece of feedback for the driver and occupants. Hence, road tests for each type of vehicle is critical to determine cabin noise and vibration levels inside the car.

I performed a road test in a Mazda CX-7 to understand the techniques used to measure and analyze vehicle noise and vibration from on-road excitation. I then analyzed the characteristics of noise and vibration signals obtained from different types of road surfaces, and the differences in the spectral content at different locations on the vehicle due to isolation and resonances. 

Method:

The Mazda CX-7 was instrumented to measure interior sound pressure (using microphones) as well as vibrations (using single axis accelerometer) on the spindles, seat track, and steering column. The vehicle was driven on a variety of road surfaces such as smooth road, brick road and rumble strips. Data was recorded for a period of several seconds at a time using the Mueller-BBM data acquisition system.

Siemens Testlab was used to post process the data to find the source of sound and vibrations from different parts of the vehicle. (We also ended up identifying the distance between each rumble strip in the road using data – This was just a side exercise) 

Result:

I understood the concept of acoustic cavity boom, analyzing third octave spectrum plots of different road surfaces and how different road surfaces can affect the frequency content of the interior sound.