This study has been motivated by the problem of the suppression of the acoustical feedback in audioconference rooms. The echo cancellation algorithms are based on a finite impulse response of the room involving a very large number of coefficients. In order to reduce the complexity of the algorithm simpler models similar to those used in digital reverberators have been used. They did not yield significant gains in the adjustment of the model. Another approach is introduced to simplify the computation; it is based on the non stationary behaviour of the acoustical impulse response.