Coordinated Treatment of Automobile Noise and Vibration

Abstract

The object of this paper is, first, to consider the various sources of mechanical vibration and noise in the automobile together with their respective characteristics and treatment; and, second, to attempt by analysis of available data to show a fundamental coordination in human reaction to noise and vibration. For the most part, noise and vibration have always been treated as independent problems both as to their origin and effect. Actually, they are so closely related in both respects that intelligent approach to the job of promoting passenger comfort in automobiles requires broad visualization of noise and vibration as coordinated phenomena. In outlining the various sources of mechanical vibration and noise, they are to be treated both in their independent and interrelated aspects. The vibration sources are subdivided into external disturbance to vehicle, engine dynamics and unbalance in drive members: independent noise sources to be considered are road surface factors, tire characteristics and those directly excited by engine operation. In each case, the method of treatment will be discussed from the standpoint of practical necessity for obtaining maximum results at minimum cost. The available data with regard to human annoyance factors, while meagre, are sufficient for developing an analytical method of coordinating noise and vibration reactions. Using Professor Jocklin's data on human vibration tolerance, and Hale Sabine's data on equal annoyance noise levels, it will be shown that when both types of disturbance are expressed in the same dimensional units, a similar characteristic variation of tolerance with frequency is indicated. The hypothesis is advanced that noise, having been generated by mechanical vibration, is reconverted by the mechanism of hearing into analogous disturbance of the human organism to that set-up by directly transmitted vibration. Much further research is essential to establish a definite quantitative relation between the two types of excitation. Eventually, it should be possible to integrate both the noise and vibration present in a given environment to obtain a single resultant human discomfort factor.