Sound absorption can be used to control noise by reducing the reflected energy of an incident sound wave striking a surface. In this work, the behaviour of a sound absorbing unit composed of two tensioned impermeable membranes and two air cavities is discussed. Analysis is performed for normal-incidence sound pressure waves. The sound absorption coefficient is determined from the average input impedance of the unit. The total impedance of the system is calculated from the solution for the axi-symmetric vibration of a forced clamped membrane and using the translation impedance method. It is shown that the sound absorbing properties of the unit can be adjusted by modifying the values of tension, density, and separation distance between the membranes.