Abstract
Ventilation ducts can have a negative effect on the sound reduction index between two rooms if they pass through the dividing structure without treatments. The overall sound reduction of a ventilation duct is dependent on several factors including the transmission loss when sound is breaking in and out from the duct. This study aims to model the sound reduction of a combined system with a separating wall and a ventilation duct through it. Three walls, characterized according to ISO 717-1, are combined with three different ventilation ducts, two circular and one rectangular with different dimensions. Laboratory measurement data are used to determine the sound reduction of the different configurations and the type of treatments needed for each configuration. A proposed model with existing theory for describing sound transmission losses of circular and rectangular ventilation ducts predicts the shape of the measurement data for many frequency bands. A new theory part is developed through an iterative process for circular ducts, which is based on measurements with previous methods and studies as a guide because the existing prediction scheme is somewhat perplexing. For rectangular ducts, the existing theory has been updated to better match measurement data. The application of the proposed theory and model in this article shows similar results when compared to measurements. The difference in weighted sound reduction index between developed theories and measurement data is 0–1 dB for every configuration.
Highlights
The sound that is produced in one room can propagate to adjacent rooms by several paths
Larger ventilation ducts are mostly used in offices, schools and hospitals whereas smaller ducts are used in dwellings
Cases 3–5 were used to investigate which treatments are required for the ventilation duct to not reduce the sound reduction index of the separated wall compared to the reference wall
Summary
The sound that is produced in one room can propagate to adjacent rooms by several paths. The indirect construction paths are not considered in this article Another complexed path is via the ventilation duct when, for example, the duct goes from one room to another through a separating wall [2,3]. With this configuration, sound can propagate via the material of the ventilation duct and via the air inside. For pipes and smaller ventilation ducts, it is often sufficient to apply a sealant as a treatment between the tube and the wall for the pipe (or duct) to not affect the sound reduction of the separated wall [4]. There are some theories to calculate how much the ventilation duct will affect the sound reduction of the separated wall, which depends on if the sound breaks in or out from the duct [5]
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