The research of a trade-off between loudness and sustain (duration) is a major issue for piano designers and manufacturers. The way the energy of vibration is transferred from the piano string to the soundboard depends on the end conditions of the strings at the bridge: these conditions can be approximated by the input admittance at the connecting point between the string and the resonator. Therefore, proper measurements of this value are needed. Given this, we propose here a method of validation of admittance measurements on simple structures. Parameters such as frequencies and damping factors of the string partials depend directly on the end conditions. The analysis of the vibratory signal of the string, based on high resolution estimation methods (ESPRIT algorithm), allows us to evaluate efficiently those parameters and leads to the calculation of the input admittance. This method is implemented on a simplified device composed of a piano string coupled to a thin steel beam. The comparative study of two experimental cases (isolated string and string coupled) leads us to the input admittance. This value, deducted from vibratory measurements of the string is eventually compared to direct admittance measurements effected on the beam, in order to validate the method. The poster in pdf can be downloaded here: http://kerem.nathan.ege.free.fr/ISMA2007_Ege_Chaigne_poster.pdf