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 (500-1) 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 (500-2) 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 (A) 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 at least partly defines a flow passage through the impeller , and the first moulded part (500-1) and the second moulded part (500-2) are separately moulded and assembled together, or the second moulded part (500-2) comprises a different material than the first moulded part (500-1) and is overmoulded to the first moulded part (500-1). 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 (500-1) 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 (500-2) comprising a hub structured for coupling to the rotor and a second shroud , a first moulded part (500-1) 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 (500-2) 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 (A) 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 at least partly defines a flow passage through the impeller , and the first moulded part (500-1) and the second moulded part (500-2) are separately moulded and assembled together, or the second moulded part (500-2) comprises a different material than the first moulded part (500-1) and is overmoulded to the first moulded part (500-1). a diameter of the impeller is less than about 50 mm, each shroud at least partly defines a flow passage through the impeller , and the first moulded part (500-1) and the second moulded part (500-2) are separately moulded and assembled together, or the second moulded part (500-2) comprises a different material than the first moulded part (500-1) and is overmoulded to the first moulded part (500-1). <EOS>