INTRODUCTION This Item provides a computerized means of estimating the sound power attenuation due to the introduction of acoustically absorbent linings in circular ducts from a knowledge of the normalized acoustic impedance of the linings at each frequency. The computed result may also be interpreted as the liner insertion loss@ defined as the reduction in sound power following the introduction of the duct liner. The prediction method used is based on a theoretical model which allows a selection of typical velocity profiles across the duct. The program has the capability to consider up to ten different liner sections in series in a circular duct of constant cross-sectional area. The Item addresses the total power reduction within the duct and does not consider subsequent radiation to the far-field.