Interaction of sound waves with glow discharge plasma was studied experimentally, as a continuation of the work reported earlier [1,2]. The main thrust of this investigation was to determine the effectiveness of using glow discharge plasma as a sound barrier in aerospace applications. The present study focused on the determination of the mechanism for attenuation of sound passing through a glow discharge. Experiments were conducted in an anechoic chamber where the attenuation of a single frequency (12.5 kHz) sound propagating through a plasma sheet formed between two electrodes was studied. The attenuation was measured at different locations inside the chamber with the discharge plane normal to the direction of sound wave propagation and at a 45-degree angle to that where attenuation in the axial direction by 23.5 dB was obtained. The experiments established strong reflection of the acoustic wave from the glow discharge region. Evidence that the dominant mechanism responsible for the observed phenomenon is the change of the index of refraction due to gas temperature gradient in the boundary regions of the plasma was obtained.