A drive-by exterior noise program was conducted to determine the contribution of each car noise source-engine/exhaust, fan, and tire/roadway-to the total exterior drive-by noise of a passenger vehicle. A 1970 high- and low-power sedan and a 1970 high- and low-power sporty compact were utilized in the test sequence.
Octave-band and dBA sound levels were recorded with the microphone positioned 25 ft away for various modes of vehicle operation at cruise and wide-open-throttle conditions.
Results indicate for cruise (road-load) conditions that:
Except for high-performance vehicles, the predominant source of exterior vehicle noise above 500 Hz is tire/roadway noise.
The major sources of exterior noise below 500 Hz are both engine/exhaust noise and tire/roadway noise.
Fan noise is an insignificant contributor to passenger vehicle exterior noise at present noise levels.