A positive airway pressure device (2, 602, 802, 902, 4002) comprises: a casing (5, 605, 805, 2905, 4005)； and a blower (10, 610, 4010) provided within the casing, the casing including at least first (6(2), 606(1), 806(1), 4006(1)) and second (6(3), 606(2), 806(2), 4006(2)) chambers and a plurality of conduits (105, 607, 807, 907, 1605, 1705, 4007-1) that allow air to pass from the first chamber to the second chamber, the plurality of conduits arranged to provide acoustic impedance and flow measurement by providing a defined pressure drop.
