Measurements have been made on the performance of an anechoic chamber built for the National Research Council of Canada, adopting the inverse square law as the criterion of performance. Some deviations from the inverse square law were observed, and these were correlated with vibrational modes in the wedge bearing inner walls. It was shown that maximum amplitudes of vibration occur in certain regions of the walls and occupy frequency ranges which coincide with frequency ranges for maximum deviations from the inverse square law. The phase of the vibrations along the walls varies in the same manner as the phase of the incident sound wave in the room. Blocking all experimental points in one of the walls improved room response by a small but consistent amount. Treating regions of maximum vibration in the walls as extended sources and combining contributions from these with the sound field of the source in the room, it was possible to construct room characteristics similar to those observed.