Acoustic behaviour of plates made of different materials for measurements with the microphone flush mounted

摘要

Different possibilities for the location of the microphone are provided when it is desired to determine the sound levels outdoors. With regard to this topic, the ISO 1996-2 standard proposes a series of corrections depending on the distance to the facade of the buildings to evaluate the incident sound field, thus correcting the effect of reflections. In this regard, in the case of the microphone located on a reflecting surface, the standard establishes two options: on the one hand, to place the microphone directly on the facade, and on the other hand, to use a plate on the surface. This work shows a comparative study of the acoustic behaviour of two plates with identical geometries through in situ measurements, both in broadband and frequency bands. One of them is made of aluminium, following the explicit recommendation of the ISO 1996-2 standard. The other plate is made of methacrylate to look for a less dense material and, consequently, to obtain a plate that is more easily transportable. Different measurement conditions have been considered to evaluate the differences and similarities between the two plates. The results obtained in different measurement configurations show an equivalent acoustic behaviour of both plates. Consequently, the alternative use of a methacrylate plate instead of an aluminium plate could be considered adequate according to the indications of the ISO 1996-2 standard.