Effects of Windshield Thickness and Construction on Passenger Vehicle Interior Noise

The purpose of this work was to measure on-road the objective and subjective changes in vehicle interior noise due both to changing from the current 3-ply windshield construction to an experimental 2-ply windshield and to changing the thickness of the single glass ply in the 2-ply construction. Measurements and subjective ratings of interior noise were made under a variety of test conditions in two nominally identical vehicles. One vehicle served as the “baseline” vehicle, while the other vehicle contained the particular windshield under test. Test conditions were chosen to study how the interior noise due to the intrusion of traffic noise, engine noise, road noise, windrush noise, raindrop noise, and wiper blade-on-windshield noise was changed by the various windshields. A jury of test subjects rated the interior noise on a 10-point scale in both front and rear seat positions in back-to-back rides in the two vehicles. In addition, overall sound pressure levels were recorded and spectral measurements were made. In general, it was found that a switch from a 3-ply to a 2-ply construction increases only those contributions to interior noise due to windrush and impact type events such as rainfall. Reducing the glass thickness in the 2-ply construction from 4 to 3 mm was found to increase the interior noise of impact type events only. While the effect of windrush noise could be minimized by careful attention to flush mounting the windshield and the use of recessed wipers, an increase in impact type noise levels is an unavoidable problem for thinner windshield constructions. The only way to overcome annoyance due to the latter is to increase glass thickness until the proper “balance” of interior noise is achieved.