This paper presents the results of a theoretical and experimental investigation into the acoustic scattering matrix for a centrifugal pump. Background is provided which examines past research into acoustic two-port models, illustrating the benefits and laying the groundwork for the current incarnation of the scattering matrix. The results reveal that the traditional form of the transmission matrix is not adequate for predicting the parameters of the scattering matrix and a new form is suggested. With a simple modification, the predicted values successfully capture the trend in the experimental data. The presented research is still ongoing, looking to improve the model by including the compliance of the pump housing and inertial effects at the pump ports.