A compact respiratory therapy device suitable for use by a patient during sleep to provide respiratory pressure therapy, the device comprising: a housing; an inlet; an outlet; a motor including a rotor; an impeller configured to be rotated by the rotor to deliver a flow of air from the inlet toward the outlet, the impeller comprising: a first moulded part comprising a plurality of impeller blades, each impeller blade comprising a leading edge and a trailing edge; and a first shroud comprising a wall defining a periphery of a center opening of the impeller, the center opening providing an impeller inlet of a flow passage through the impeller; and a second moulded part comprising a hub structured for coupling to the rotor and a second shroud, wherein the compact respiratory therapy device is configured to deliver the flow of air from the outlet for delivery to the patient at a pressure between 4-30 cmH2O at an overall sound power level of less than 50 dB thereby reducing any disturbance to a quality of sleep for the patient, and wherein: a diameter of the impeller is less than about 50 mm, each shroud (520, 525) at least partly defines a flow passage through the impeller, and the first moulded part and the second moulded part are separately moulded and assembled together, or the second moulded part comprises a different material than the first moulded part and is overmoulded to the first moulded part. a housing; an inlet; an outlet; a motor including a rotor; an impeller configured to be rotated by the rotor to deliver a flow of air from the inlet toward the outlet, the impeller comprising: a first moulded part comprising a plurality of impeller blades, each impeller blade comprising a leading edge and a trailing edge; and a first shroud comprising a wall defining a periphery of a center opening of the impeller, the center opening providing an impeller inlet of a flow passage through the impeller; and a second moulded part comprising a hub structured for coupling to the rotor and a second shroud, a first moulded part comprising a plurality of impeller blades, each impeller blade comprising a leading edge and a trailing edge; and a first shroud comprising a wall defining a periphery of a center opening of the impeller, the center opening providing an impeller inlet of a flow passage through the impeller; and a plurality of impeller blades, each impeller blade comprising a leading edge and a trailing edge; and a first shroud comprising a wall defining a periphery of a center opening of the impeller, the center opening providing an impeller inlet of a flow passage through the impeller; and a second moulded part comprising a hub structured for coupling to the rotor and a second shroud, wherein the compact respiratory therapy device is configured to deliver the flow of air from the outlet for delivery to the patient at a pressure between 4-30 cmH2O at an overall sound power level of less than 50 dB thereby reducing any disturbance to a quality of sleep for the patient, and wherein: a diameter of the impeller is less than about 50 mm, each shroud (520, 525) at least partly defines a flow passage through the impeller, and the first moulded part and the second moulded part are separately moulded and assembled together, or the second moulded part comprises a different material than the first moulded part and is overmoulded to the first moulded part. a diameter of the impeller is less than about 50 mm, each shroud (520, 525) at least partly defines a flow passage through the impeller, and the first moulded part and the second moulded part are separately moulded and assembled together, or the second moulded part comprises a different material than the first moulded part and is overmoulded to the first moulded part.