Abstract: A sound source located inside a tube having one end inside the mouth or nose of a subject provides an acoustic transient signal that propagates into the respiratory system of the subject to provide reflections sensed by a single mircophone inside the tube between the sound source and the mouth of the subject for recording on a transient recorder or computer and display on an oscilloscope after passing through a low pass filter to provide an output signal representative of the acoustical properties of the airways of the subject. This output signal may be processed in accordance with the deconvolution integral and other algorithms to determine essentially the acoustic impulse response, impedance or effective cross-sectional area of the airways, typically as a function of the distance from a reference point, such as the end of the tube.