Impact of low frequency road traffic noise on indoor environments for different facade structures

Abstract

Road traffic noise is a major environmental problem in Europe where at least 20 percent of the EU population live in areas where traffic noise levels are harmful to health. Recent changes and regulations in Swedish law enables a higher sound pressure level at facade, making it easier to build closer to roads. Typical noise reduction measures improve sound insulation at mid and high frequencies well, while not being as effective at lower frequencies of 20–200 Hz. As a consequence, more low frequency traffic noise indoors can be expected as we build closer to trafficked streets. This thesis aims to investigate the effect of low frequency traffic noise inside dwellings where (1) a study of traffic modelling and field measurements on a selection of different facade structures is made to determine the indoor low frequency traffic noise and (2) a psychoacoustic study is carried out where the annoyance level from low frequency traffic noise is investigated through listening tests. The measurements suggest that none of the studied apartments have good insulation for low frequency noise. For all of the studied facades, peak pass by sound levels due to heavy vehicles are above our audible threshold and also at certain frequencies above the recommended Swedish guidelines for indoor low frequency equivalent levels. The listening test suggests that the largest annoyance for inhabitants inside dwellings comes from heavy vehicles while light vehicles pose no greater annoyance even if the peaks of the low frequency sound levels inside the dwelling are above the equivalent level guideline values. Furthermore, the listening test results suggest that the annoyance that inhabitants experience is not only from low frequency components from vehicles passing by at a constant speed with no significant tonal changes. Instead they suggest that the low frequency components constitute the annoying part when there are clear tonal changes such as in situations with accelerating vehicles.