The systems, apparatus and methods described herein provide a quiet, light-weight, and portable system and apparatus for providing positive air pressure to a patient. The application discloses a CPAP apparatus (100, 300, 400, 500, 600, 700, 900) comprising: a housing (180, 380, 381, 780, 784, 980) defining a first acoustic chamber (402, 502, 602, 930) with a first inlet port (412, 512, 612, 613, 910), and a second acoustic chamber (414, 514, 614, 934) with a blower unit (140, 416, 516, 616, 740, 940) and a second inlet port (422, 507, 622, 917) extending from the first to the second chamber. The CPAP apparatus can be portable. A system can comprise the apparatus comprising an adapter (160, 360, 760, 960) in communication with the blower unit and extending outward from the apparatus, and a detachable patient interface system (165, 365, 965). The apparatus can include alternatively a single acoustic chamber (130, 230, 730) with an inlet port (110, 710) most of whose length is within the acoustic chamber, and an outlet port (139, 739). The blower unit can be vibrationally isolated. The dimensions of inlet ports and acoustic chambers may be proportionally related, in particular defining an acoustic low-pass filter. The application discloses a method for reducing noise in a portable CPAP device with first and second acoustic chambers, including routing the flow of air through the device, wherein the first inlet is sealed from and passes through the second chamber into the first acoustic chamber, and the flow of air is routed through an outlet port sealed from and passing through the first chamber.
