In this paper we apply a new method to obtain the dynamical characteristics of premixed flames in acoustically complex systems like an annular combustor. For this a novel model based reduction method was applied which describes the acoustic field as a superposition of a discrete number of eigenmodes. The measured dynamic signals are decomposed into modal components which are then used to fit the model parameters. With this approach the complete characterisation of the annular test rig requires significantly less experimental effort, i.e. simultaneous pressure measurements, than before. After describing the new procedure, we show the validation of the acoustical model. Using this model, we were able to obtain the characteristics of the flame in the annular combustor with a much smaller number of pressure sensors as the model provides physical constraints that would otherwise have to be measured. The comparison of the characteristic flame parameters between the single burner and the annular combustor configurations for the same operating conditions shows that in the annular combustor slightly longer convective time delays are found which are consistent with the static flame characterisation showing longer flames in the annular combustor than in the single burner test rig.Copyright © 2008 by ALSTOM