This article presents an experimental study of self-sustained instabilities of an ensemble of premixed flames anchored on perforated plates. A theoretical analysis based on experimental results is developed in order to model the acoustic-flame coupling. In the unconfined configuration envisaged in this study, the coupling occurs with the upstream cavity. Experiments carried out on this multipoint injection configuration concern the acoustic response of the system and the influence of the perforated plate impedance, the emission of sound by the flames and the combustion transfer function. The thickness of the perforated plate is an important parameter that modifies the resonant frequencies and the ranges of instability. Instability bands determined by the model are in good agreement with experimental data, providing a suitable explanation of the mode hopping process characterizing such configurations. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.