A filter assembly for a data storage device. The filter assembly includes a flow passage having an inlet and outlet to provide a recirculating filter. The filter assembly is positioned to provide a pressure differential between the inlet and outlet of the flow passage. A breather filter includes an opening for ambient air exchange through a second flow passage which is opened to the pressure differential of the flow passage of the recirculating filter to enhance ambient air exchange. An air dam assembly interposed in an air flow path provides a high pressure region and low pressure region. An assembly structure includes an air dam and a filter flow passage to enhance the pressure differential across the flow passage. Flow turbulence through the flow passage is reduced via flow plates supported between raised edge portions of the flow passage.