did not include the value at 125Hz (128Hz at the time). Factors affecting noise reduction coefficient Mounting type The NRC is highly dependent on the type of mounting, which, if not specified, is usually a Type A mounting (ABPMA mounting #4) where the material is placed directly on the floor, wall, or ceiling. Acoustical ceiling tiles are often tested in Type E400 mounting, which simulates a 16 inch-deep plenum. This deeper airspace typically boosts the low frequency performance of the tile, but may not impact the NRC rating (since the NRC does not include the 125Hz octave band). Sample size There's potential for greater error or overemphasizing the acoustic efficacy of a material if tested sample sizes are smaller than the standardized 8ft x 9ft modules. The perimeter-to-area ratio has a significant effect on the overall sound absorption of a material, and may effect the NRC. Thickness Thicker samples of the same material often absorb more sound and are better at absorbing lower in frequency. Thicker materials also have larger surface area at the sides, resulting in increased sound absorption due to edge effects. Applications NRC is most commonly used to rate general acoustical properties of acoustic ceiling tiles, baffles, banners, office screens, and acoustic wall panels. It is occasionally used to rate floor coverings. NRC is intended to be a simplified acoustical rating of room construction and finish materials when the acoustical objectives of the space are less than sensitive. The NRC average is rounded to the nearest 0.05 due to a typical lab repeatability of ±0.05 for 2 standard deviations. Reproducibility between different labs is roughly three times higher at ±0.15 for 2 standard deviations. NRC is a useful rating for general purpose rooms where speech noise build-up is the major concern: lobbies, open offices, reception areas, etc. In certain applications, such as designs of music rehearsal rooms, performance spaces, and rooms employed for critical speech, it is usually more appropriate to consider the sound absorption coefficients at the individual one-third octave band frequencies, including those above and below the bands used to compute NRC. When evaluating the NRC of similar materials, the following table can be used to approximate whether there's an aural difference: New standards NRC is being replaced by the Sound Absorption Average (SAA), which is described in the 1999 and newer versions of the ASTM C423 standard. The SAA is a single-number rating of