The objective of this study is to determine the impact of a time-varying room impulse response on the rate of adaptation and accuracy of monaural and stereo echo cancellers. The variation in the impulse response results from secondary echoes generated by moving objects in a room. The time- invariant portion of the response is modeled using the method of images. The time-varying component will be modeled using a Pade approximant- based solution of the Kirchhoff integral equation. Simulation results are given for a room having a volume on the order of 2744 cubic feet. It is shown that for strong acoustic scatterers located closer than the critical distance to the receiver can induce up to a 15-dB residual error for monaural cancellers. Adaptation time requirements for acoustic echo cancellers will also be discussed.