Characteristics and sources of noise and vibration and their control in motor cars

A detailed study of the characteristics of noise and vibration in a motor car is described. The predominant frequency regions in which noise levels are high are established. It is shown that the major part of the sound energy lies within the frequency region below 20 Hz and is caused mainly by road excitation being transmitted through the wheel and suspension system. The predominant noise in the audible range lies within 30–300 Hz frequency band and is produced primarily by body resonances excited by various engine harmonics. The vibrational and acoustical behaviour of the car body at some of these critical frequencies is also discussed. Finally it is shown that by structural modification a substantial noise reduction can be obtained.