Model Studies of Effects on Motor Vehicle Noise of Shapes and Arrangements of Buildings along Urban Streets. II. Experimental Findings

Descriptions are given of the various models investigated and the acoustical characteristics of the noise sources simulating motor vehicle noise. The models tested correspond to streets of typical widths, faced with buildings of typical heights, having various shapes and orientations (conventional and modified), with and without spacings (alleys), and with the facing surfaces either reflective or absorptive. One series of curves, using the gasoline engine as the noise source (operating at low and also at high speed), shows sound-pressure levels versus the horizontal transverse distance across the model for five wall separations ranging from 10 to 30 ft. The levels agree with predictions. Similar curves show dBA and octave-band levels versus the longitudinal distance along the base of one wall, for both continuous and spaced walls. The curves reveal the anticipated effects of diffraction. Noise reductions of as much as 12 dB were obtained by the use of oblique, flat surfaces at the wall bases. This encouraging result is being followed with tests on models for buildings having appropriate parabolic facings. The findings have predictive value for full-scale constructions.