A respiratory therapy (RT) system including one or more acoustic generators (8500) to produce an inaudible acoustic signal. The acoustic generator(s), such as when coupled to a patient interface or air circuit of a respiratory therapy device, may provide inaudible acoustic signals indicative of one or more parameters, such as a flow rate or a pressure of the flow of air, or a type of or useable life of a component (e.g. patient interface). The system may have an acoustic receiver that may detect one or more acoustic signals from the acoustic generator, the RT system, the patient or the environment.