Microphone position and noise exposure assessment of building façades

Abstract

The prevention or reduction of the exposure of the population to environmental noise is the fundamental objective of the European Noise Directive (END). To this end, strategic noise maps are considered as the basic tool and on-site measurements play an important role in its successful implementation. In this regard, the ISO 1996 standards are the reference for the measurement and assessment of environmental noise, but their application may be complex in many cases. It is therefore necessary to find urban scenarios in which the effects of the placement of the measuring equipment with respect to the façade on noise exposure levels can be analysed.In this study, an educational building was selected for an analysis of the differences in the weekly sound level from road traffic between a microphone flush-mounted on a plate at the façade and another placed between 0.5 and 2.0 m from it. The recommendations in Annex B of ISO 1996-2 were followed in the placement of the microphones. A broadband analysis shows that similar results were found for the four distances analysed, but that variations of up to 0.6 dBA above the reference value arose. An analogous study using frequency octave bands shows differences higher than 2 dB between the measured configurations for bands under 250 Hz. Based on the distance range given in ISO 1996-2 for the position of a microphone in front of a reflecting surface, the results suggest that the most appropriate option for accurately assessing the sound level incident on the façade of buildings is to place the microphone at a distance of 2 m if the guidelines of the ISO 1996-2 standard can be met.