Airway area by acoustic reflection: A corrected derivation for the two-microphone method

A corrected derivation is provided for the relationship between the impulse response of a wave tube termination and pressure signals measured at two d ifferent locations within the tube. This derivation yields exactly the same final result as was reported previously by LOLII'S et al. (1993), despite the omission of the active source term in that earlier derivation. This tec hnique has become the basis of an important medical diagnostic technology. This report revises and corrects the earlier theory upon which that technol ogy rests.