Acoustic energy measurements were carried out in a coal-burning Rijke combustor using a hot-wire anemometer probe and a furnace microphone probe. The acoustic power output of the combustion region was found to increase with the coal-bed thickness. A minimum coal-bed thickness was found to be necessary for sustaining the acoustic oscillations, and it was found that stable operation was not possible for large coal-bed thicknesses. Substantial acoustic power was found to be lost from the tube ends. Measured tube-end impedances were found to be dependent on the coal-bed thickness, and were of a magnitude consistent with the authors' expectations in earlier work. A phase difference was found to exist between the unsteady heat release and the pressure oscillation in the combustion zone. This result is also consistent with criteria derived in the authors' earlier theoretical work. The amplitude of the unsteady heat release as a fraction of the steady heat release was obtained as a function of the bed thickness.