The acoustic performance of circular openings and wall-mounted vents

Abstract

Outdoor air intakes (vents) adversely affect the sound insulation of a building envelope. The purpose of the research was to investigate how different components of the wall-mounted vent and the vent-wall geometry influence its acoustic performance, and to provide practical guidelines that can be used in the design and testing of such devices. The study is based on laboratory measurements. Three basic questions are discussed: the test facility, the effect of a circular opening in a wall and the performance of a vent installed in the opening. A double partition wall should be used in the laboratory to suppress flanking transmission and provide reliable results. Low frequency modal effects related to a sample position in the wall did not influence the single number quantities. Circular openings exhibited fundamental resonance depending on the wall thickness, the diameter of the opening and the end reflection conditions. These effects contributed to the sound transmission loss of a complete vent. The vent components are effective mostly at high frequencies, as low frequency bands are controlled by the wall, while the improvement of middle frequencies is still a challenge. Aside from resonance, the combined sound insulation of particular vent components was approximately the same as that of the complete integrated unit.