Comparative laboratory analysis of window sound insulation across glazing types in the 50–5000 Hz range: evaluation of different low-frequency methods

This study investigates the sound insulation performance of windows by presenting laboratory measurements from 50 to 5000 Hz on two window types, with and without an integrated shutter box, each tested across five glazing configurations. While all measurements were conducted under controlled laboratory conditions, particular attention was given to the low-frequency range (50–100 Hz), where every measurement method available in the standard was applied. These included procedures based on the laboratory standard (ISO 10,140), the in situ standard (ISO 16,283), and a hybrid approach, all implemented within the laboratory setting. The results reveal that below 100 Hz, sound insulation values and differences between window types vary significantly depending on the measurement method. The in situ procedure, when applied only to the receiving room—as is common in façade assessments—yields the lowest insulation values and minimizes differentiation between window types, likely due to room modal effects. In contrast, applying the same procedure to both the source and receiving rooms produces results that more closely align with those obtained using laboratory standards. Furthermore, while the window without a shutter box generally provided higher insulation above 100 Hz, it exhibited a more pronounced reduction in insulation below 100 Hz under laboratory conditions, highlighting a potential source of low-frequency discomfort not reflected in standard manufacturer ratings. These findings underscore that low-frequency sound insulation ratings are highly dependent on the measurement approach, emphasizing the need to refine standardized protocols and enhance the reliability and perceptual relevance of acoustic descriptors in this frequency range.