Question

wha is NRC ? Explain it.

Answer 1

The first NRC was prepared in 1951,[1][2] 1951 Census of India.[3]


The NRC Update of 2014–2016 across Assam includes the names of those people (or of their descendants) who appear in the NRC 1951, or in any of the Electoral Rolls[4] up to the midnight of 24 March 1971[5] or in any one of the other admissible documents issued up to the midnight of 24 March 1971, which would prove their presence in Assam on or before 24 March 1971.

Answer 2

'NRC '(Noise Reduction Coefficient) is a number that rates the capability of a material at absorbing sound (absorbing energy). Why would you want to absorb energy?

In an environment where you have reflective surfaces (hard floors, bare walls, long desks, bare ceilings) the sound emitting from a source can reflect and grow in size causing reverberations.

I am not saying that all reverb is bad. For example, a choir singing hymns within a large church takes advantage of this natural reverb and they really complement each other. However, you would not want the same reflections or reverb times in a lecture hall or large office space. It can disrupt conversations between colleagues, lower productivity and learning. This is why we need to place materials around the environment to help absorb some of this energy.

The Noise Reduction Coefficient is calculated by averaging how absorptive a material is at four different frequencies: 250hz, 500hz, 1000hz, and 2000hz. (The lower frequencies are harder to absorb because the wavelengths are so long). The 250 to 2000hz is an average mid-range speech frequency. This implicates that using the NRC value for a product to absorb music (full frequency range) is pointless.

After each material is tested, it is given an NRC rating. This can range from 0 to 1.00. Ratings are rounded to the nearest .05 These values can exceed 1.00 when thick materials or materials with large air spaces are being tested. Also, a test material’s area does not include the sides of the panel, which are exposed to the test chamber. Depending on the thickness of this, NRC results can vary.

However, because the official NRC is an average, two materials with the exact same NRC can perform differently in different circumstances - E.g. Each may absorb better at different frequency levels, but may work differently in alternate environments.