Experimental Comparison of Sound Transmission via Ventilation Ducts: Sheet Metal vs. Glass Wool Systems

The increasing use of mechanical ventilation systems in energy efficient buildings introduces a significant pathway for acoustic crosstalk between rooms via air ducts. Air ducts connecting rooms can reduce airborne sound insulation, and therefore such systems can affect acoustic comfort not only through the noise they generate. This article focuses on a common situation where air ductwork located outside of ventilated rooms has branches leading into rooms (e.g., ventilation system in ceiling plenum in corridor connected to habitable rooms in apartment). The study provides new experimental data on sound transmission through ventilation ducts. Various materials (steel and glass wool pre-insulated ducts) and duct configurations were investigated. The results are presented by means of normalized level differences specific to the ventilation system, Dn,s, to facilitate their further use, e.g., for predictions of total airborne sound insulation between rooms according to ISO 12354-1:2017, which contains a prediction model enabling the combination of Dn,s,w of the system with Rw of the wall. The results show a significant variation in sound insulation (Dn,s,w) from 37 dB (for sheet metal system) to 73 dB (for glass wool system), which implies that sound-absorbing ductwork provides considerably higher acoustic comfort. The acoustic performance of traditional sheet metal ductwork was highly dependent on terminal elements and was often insufficient to meet common sound insulation requirements, whereas ductwork made of sound-absorbing materials provided consistently high insulation.