While most people keep a high attention to the significance of the binaural recording method, whether it is e.g. individual or non-individual (as e.g. artificial head recording), many pay less attention to the type of earphone used to reproduce the binaural signals, and to the accurate control of the ideal 1:1 reproduction of the signals at the eardrum. This paper identifies and discusses two special cases of earphone reproduction. Further work on the analysis and quantification of calibration errors is planned.