Measuring sound insulation of building facades: interference effects and reproducibility

Sound insulation in buildings is getting increased importance both in national regulations and in international standards. Consequently, accurate and reliable measurements are of the greatest importance in order to compare and discuss building performances. The determination of sound insulation of building façades requires the measure of both outdoor and indoor sound pressure levels. Unfortunately, the standard measuring procedure for façade insulation has shown several limits, especially with reference to outdoor pressure level. The placement of source and receiver, which is kept flexible to adapt to building characteristics, opens the way to possible interference effects which may affect different frequencies according to the given position. Comparisons between different source-receiver combinations are hence investigated theoretically and then compared with laboratory and onsite measures. The paper investigates possible destructive interference of sound waves and their influence on final results, after having described the elements that can influence the measure. Finally, the recent attention for reproducibility of acoustics measures implies the capacity to understand reasons for unexpected measures in order to be able to avoid them. The grade of reproducibility is investigated, and the variance of sound insulation of building façade is given.