Impedance measurement techniques for one-port and two-port networks

A microphone array impedance matrix measurement technique is presented for linear and passive acoustic two-port networks. Two impedance tubes fitted with three non-uniformly spaced microphones are required in the measurement. The non-uniform spacing is intended to avoid ill-posedness problems in calculating two plane-wave components traveling in opposite directions. Based on the one-port measurement, acoustic two-port networks modeled with the source and the load connected are examined. Three experimental procedures, the two-load measurement method (TLMM), the reciprocal-constrained method (RCM), and the reciprocity-symmetry-constrained method (RSCM), are developed to measure the acoustic impedance matrix. Experiments are conducted for several acoustic two-port systems to verify the proposed techniques. The results demonstrate the efficacy of the three experimental procedures when applied to symmetrical and reciprocal systems. For asymmetrical systems, the TLMM and RCM are preferred over the RSCM for measuring the impedance matrix. On top of that, the non-uniform array in conjunction with TLMM is extended to a general electroacoustic two-port system, which can be regarded as a unique contribution of the present work.