The application of active control to brass instruments brings many benefits to composers and performers, by expanding its sound possibilities. In this paper, we propose to simulate the connection of a static human vocal tract, downstream of the bell, so that the instrument radiates a vowel. To this end, we modulate the spectral envelope of the radiated sound by a series of formants, namely the vocal tract resonances. Using source-filter modeling and the laws of linear acous- tics, this amounts to introducing the transfer function of the vocal tract between the resonator and the natural radi- ation impedance of the instrument. The vocal tract model is a succession of straight tubes of constant cross-sectional areas, cascaded using the transfer matrix method. For this purpose, a controller is introduced in a feedback loop. It takes as input the acoustic pressure measured by a microphone at the bell and calculates the contribution to be added to the natural flow rate out of the bell to obtain the target flow. The actuator consists of several loudspeak- ers co-located with the microphone. The control is validated by successively simulating several target vocal tracts and by quantifying the variations of the spectral envelope of the radiated sound.