Variability in the noise testing of light motor vehicles

Abstract

There have been complaints about the variation from day to day and site to site in the noise levels of light motor vehicles when measured with standard test procedures. A study aimed at the resolution of the sources of this variation is described. A light‐, a heavy‐, and a medium‐weight automobile were each tested (repeatedly) on three different paved sites under a variety of atmospheric conditions. The levels from a calibrated point source simulating the noise from an exhaust pipe was measured under the same conditions with the source stationary, and also with the source carried through the standard pass by procedure on a coasting vehicle. Vertical gradients of ambient wind and temperature were monitored. Preliminary analysis of the results indicates that the major source of the variation is refraction in the wake of the moving vehicle.