Sound production in recorder-like instruments occurs near an open end of the resonator. The impedance of this opening, specific to flute-like instruments, acts both on the passive resonances and on the active behaviour. The geometry of this active-end is characterized by the presence of an edge needed for the sound source. This edge induces a significant enlargement of the section of the chimney associated with this opening. This study proposes a model of the frequency response of the active-end of recorder-like instruments inspired by previous works on open side holes. Predictions from this model are compared with measurements of a hand made recorder and to finite element simulations. Multiple geometrical conditions are simulated via finite elements and compared with the proposed model.