Definition of Terms

CAC (Ceiling Attenuation Class)
A measure of reduction in sound transmission via plenum path between two rooms determined in accordance with ASTM E 1414, and plotting decibel reduction (transmission loss) obtained at 16 frequencies against a standard reference curve, in accordance with ASTM E 413. This measurement is used for rating the performance of a ceiling system as a barrier to airborne sound transmission through a common plenum between adjacent closed spaces such as offices.

A ceiling system with a CAC < 26 is considered low performance,
whereas one with CAC >34 is high performance.

NRC (Noise Reduction Coefficient)
A measure of sound absorbed by a material. The single number designation represents the average of the sound absorption coefficients of a material at 250Hz, 500Hz, 1000Hz, 2000Hz rounded to the nearest 0.05 when tested in accordance with ASTM C 423. NRC rates the overall sound absorption of a material when used in an enclosed architectural space such as an office, where sound is reflected at many angles of incidence.

Light Reflectance (LR)
Acoustical ceilings are often used for the entire ceiling of a room, and, therefore, can be an important component of the lighting system. Acoustical materials usually have a non-glossy finish in white or near-white. The light reflectance of interior finish components must be known to predict the level of illumination that will be obtained in the finished space. The light reflectance of a surface is a function of the characteristics of the illuminant light source and the receptor, and the geometry of illuminating and viewing. The test method used to measure these parameters is ASTM E 1477, which utilizes an integrating sphere reflectometer as the measuring instrument and an absolute white standard against which samples are measured.

The resultant value is rated against the white standard and assigned a minimum Light Reflectance Coefficient expressed in increments of 0.01 and ranging from 0 to 1.00. These Light Reflectance Coefficients are sometimes compared to the following LR Designations:
>.75…………..LR 1