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Acoustical Materials
Published in Lewis H. Bell, Douglas H. Bell, Industrial Noise Control, 2017
Lewis H. Bell, Douglas H. Bell
Frequently, the performance of absorbing materials is given as a single number rating called the noise reduction coefficient (NRC). The NRC is just the mean or arithmetic average of the absorption coefficients at 250, 500, 1000, and 2000 Hz. For example, if we take the absorption coefficients of 1-in.-thick fibrous glass at 250, 500, 1000, and 2000 Hz (from Table 6.1) and compute the mean, we get 0.23+0.48+0.83+0.884=0.60
Applied Acoustics
Published in W. P. Jones, Air Conditioning Applications and Design, 2012
The term noise reduction coefficient (NRC) is sometimes used, being the average of αsab over 250, 500, 1000 and 2000 Hz. More often, the average absorption coefficient, α¯sab, must be calculated as follows, to establish the acoustic quality of the room α¯sab=(S1αsab1+S1αsab2+Snαsabn)/S
Architectural Acoustics
Published in Malcolm J. Crocker, A. John Price, Noise and Noise Control, 2018
Malcolm J. Crocker, A. John Price
Another parameter often of interest in assessing the usefulness of an acoustic absorber is the Noise Reduction Coefficient (NRC). As discussed in Section 1.6.1, this is simply the average of the measured absorption coefficients for the 250-, 500-, 1,000-, and 2,000-Hz octave bands expressed to the nearest 0.05. This NRC value is often useful in the determination of the applicability of a material to a particular situation.
Acoustic properties of sound-absorbing polyester fabrics woven with thick staple and thin draw textured yarn for use in interior decoration
Published in The Journal of The Textile Institute, 2019
YoungA Kang, EunNyeong Lee, KwanChul Lee, SoonMo Choi, EunJoo Shin
Sound absorption properties were evaluated from the sound absorption coefficient (Bell, 1994; Horoshenkov & Swift, 2001) measured using both impedance tube and reverberant field methods. The sound absorption coefficient is defined as a measure of the incident acoustical energy absorbed by a material over a number of specific frequencies and is usually expressed as a decimal between 0 and 1. For example, an absorption coefficient of 0.55 indicates that 55% of the incident sound energy is absorbed by the material, whereas a material that absorbs all the incident sound waves has an absorption coefficient of 1. Moreover, as a single number index of the sound-absorbing capacity of a material, the noise reduction coefficient (NRC) is calculated by averaging the sound absorption coefficient at frequencies of 250, 500, 1000, and 2000 Hz. The NRC is the percentage of sound that a surface absorbs, i.e., the percentage of sound that hits a surface and is not reflected back into the room. NRC values provide a clear and simple quantification of how well a particular surface absorbs sound in the frequency range of 250–2000 Hz (Harris, 1979).
Sound absorbing porous concretes composed of different solid wastes
Published in European Journal of Environmental and Civil Engineering, 2020
Celia Arenas, José D. Ríos, Héctor Cifuentes, Luis F. Vilches, Carlos Leiva
We measured the sound absorption coefficient of the manufactured materials with the impedance tube method (CEN (European Committee for Standardization), 2011b) in a frequency range from 100 to 5000 Hz. The thickness of the samples for the sound absorption coefficient was 40 mm. We used the ACUPRO system with two Spectronics microphones. In this study, the absorption coefficient, α, showed an average value of three samples tested. In order to represent the sound absorption coefficient as a single numerical value and make comparisons easier, the Noise Reduction Coefficient (NRC) was calculated as the average of the sound absorption coefficients at 250, 500, 1000 and 2000 Hz. Each result was obtained by testing three samples.