Duct units for delivery of air to an air supply fan and for connecting this fan to an air heater unit are disclosed. The duct unit for delivering air in one version has a narrow first section, a second, transition-type section and a wide sound attenuating, third section with these three sections extending generally vertically. Spaced apart splitters containing sound attenuating material and having side walls of perforated metal are mounted in the third section. The splitters include a central splitter and outer splitters with the latter converging inwardly towards a central axis of the third section. This duct unit also has an elbow-shaped duct section connected to the third section at its upstream end and connectible to the fan at its downstream end. In another version, the duct unit has a single, elongate splitter that extends longitudinally along at least a major portion of a second duct section and that bends through a smooth curve. The outlet duct apparatus has an elbow section of duct that bends through a smooth curve and an elongate second section connected to the elbow section. An elongate turning vane is mounted in the outlet duct and has a substantially curved first vane section and a second vane section that extends substantially upwardly.

A sound attenuating apparatus for mounting on a heat exchanging apparatus such as a cooling tower, this apparatus having an attenuator housing with vertically extending sides, a top cover and a bottom adapted for mounting on the tower. There is an annular air inlet in the bottom and an air outlet is formed in at least one of the sidewalls. Perforated interior walls are mounted in the housing and define an /airflow passageway that extends from the air inlet to the air outlet. These walls include a first annular wall section extending about and defining an outer circumferential portion of the airflow passageway and a second wall section with that is annular and extends about a substantially vertical central axis. The latter wall section defines an inner circumferential portion of the passageway. The second wall section extends generally upwardly and outwardly from the air inlet. Sound absorbing material is arranged behind the perforated walls.