text: Nuclear Regulatory Comission... no\nNational Research Coucil... no\n\nNoise Reduction Coefficient (NRC) is all about sound absorption. \nNRC is the fraction of sound energy, averaged over all angles of direction and from low to high sound frequencies that is absorbed and not reflected.\nIt's a measure, or average, of the sound (acoustical) absorption coefficient measured at four frequencies: 250, 500, 1,000 and 2,000 Hz expressed to the nearest integral multiple of 0.05\n\nVery important measure for determination of materials and clarity of sound.