Noise Rating (NR) Curves
Noise rating curves are used to ‘rate’ a noise source, the rating will derive in a single figure noise rating level that is generated from a review of the associated octave band levels. Noise rating curves, or NR curves, are often used to assess internal noise levels due to building service. They can also be used to set criteria when considering potentially tonal noise sources.
How do Noise Rating Curves Work?
NR curves are used to ‘rate’ a source of noise in to a single figure that considers the frequency content. A noise rating curve give a set of single octave bands levels. These octave band levels are compared against the source noise octave band levels. The NR level will be derived from finding lowest noise rating curve where the source noise does not exceed the level of the NR curve in any octave band. An example is given below.
In this instance, the source noise would be NR 52. The red figures in the 1000 Hz column indicates the level that is closest but does not exceed the NR 52 curve. All other octave bands from the source noise are lower below the associated NR curve. This is represented visually in the graph below.
Alternative Rating Systems
NR curves are most commonly used in the Europe. America has a similar rating system called Noise Criterion (NC) Curves. NC Curves function in the same way but the curves penalise low frequency more significantly than NR Curves. The Engineering Tool Box offers an in-depth description of NC curves.
NR Curve Table
| Noise Rating (NR) |
Maximum Octave Band Frequency Level (Hz), dB | |||||||
|---|---|---|---|---|---|---|---|---|
| 63 | 125 | 250 | 500 | 1000 | 2000 | 4000 | 8000 | |
| 5 | 39.4 | 26.4 | 16.7 | 9.5 | 5.0 | 1.6 | -1.0 | -2.9 |
| 6 | 40.2 | 27.2 | 17.6 | 10.5 | 6.0 | 2.6 | 0.1 | -1.8 |
| 7 | 41.0 | 28.1 | 18.5 | 11.5 | 7.0 | 3.6 | 1.1 | -0.8 |
| 8 | 41.8 | 29.0 | 19.4 | 12.5 | 8.0 | 4.6 | 2.1 | 0.2 |
| 9 | 42.6 | 29.8 | 20.4 | 13.5 | 9.0 | 5.6 | 3.2 | 1.3 |
| 10 | 43.4 | 30.7 | 21.3 | 14.5 | 10.0 | 6.6 | 4.2 | 2.3 |
| 11 | 44.2 | 31.6 | 22.2 | 15.5 | 11.0 | 7.6 | 5.2 | 3.3 |
| 12 | 45.0 | 32.4 | 23.1 | 16.5 | 12.0 | 8.6 | 6.2 | 4.3 |
| 13 | 45.7 | 33.3 | 24.1 | 17.4 | 13.0 | 9.7 | 7.3 | 5.4 |
| 14 | 46.5 | 34.1 | 25.0 | 18.4 | 14.0 | 10.7 | 8.3 | 6.4 |
| 15 | 47.3 | 35.0 | 25.9 | 19.4 | 15.0 | 11.7 | 9.3 | 7.4 |
| 16 | 48.1 | 35.9 | 26.8 | 20.4 | 16.0 | 12.7 | 10.3 | 8.4 |
| 17 | 48.9 | 36.8 | 27.8 | 21.4 | 17.0 | 13.7 | 11.3 | 9.5 |
| 18 | 49.7 | 37.6 | 28.7 | 22.3 | 18.0 | 14.8 | 12.4 | 10.5 |
| 19 | 50.5 | 38.5 | 29.7 | 23.3 | 19.0 | 15.8 | 13.4 | 11.6 |
| 20 | 51.3 | 39.4 | 30.6 | 24.3 | 20.0 | 16.8 | 14.4 | 12.6 |
| 21 | 52.1 | 40.3 | 31.5 | 25.3 | 21.0 | 17.8 | 15.4 | 13.6 |
| 22 | 52.9 | 41.1 | 32.4 | 26.3 | 22.0 | 18.8 | 16.4 | 14.6 |
| 23 | 53.6 | 42.0 | 33.4 | 27.2 | 23.0 | 19.9 | 17.5 | 15.7 |
| 24 | 54.4 | 42.8 | 34.3 | 28.2 | 24.0 | 20.9 | 18.5 | 16.7 |
| 25 | 55.2 | 43.7 | 35.2 | 29.2 | 25.0 | 21.9 | 19.5 | 17.7 |
| 26 | 56.0 | 44.6 | 36.1 | 30.2 | 26.0 | 22.9 | 20.5 | 18.7 |
| 27 | 56.8 | 45.5 | 37.1 | 31.1 | 27.0 | 23.9 | 21.6 | 19.8 |
| 28 | 57.6 | 46.3 | 38.0 | 32.1 | 28.0 | 24.9 | 22.6 | 20.8 |
| 29 | 58.4 | 47.2 | 39.0 | 33.0 | 29.0 | 25.9 | 23.7 | 21.9 |
| 30 | 59.2 | 48.1 | 39.9 | 34.0 | 30.0 | 26.9 | 24.7 | 22.9 |
| 31 | 60.0 | 49.0 | 40.8 | 35.0 | 31.0 | 27.9 | 25.7 | 23.9 |
| 32 | 60.8 | 49.8 | 41.7 | 36.0 | 32.0 | 28.9 | 26.7 | 24.9 |
| 33 | 61.5 | 50.7 | 42.7 | 36.9 | 33.0 | 30.0 | 27.8 | 26.0 |
| 34 | 62.3 | 51.5 | 43.6 | 37.9 | 34.0 | 31.0 | 28.8 | 27.0 |
| 35 | 63.1 | 52.4 | 44.5 | 38.9 | 35.0 | 32.0 | 29.8 | 28.0 |
| 36 | 63.9 | 53.3 | 45.4 | 39.9 | 36.0 | 33.0 | 30.8 | 29.0 |
| 37 | 64.7 | 54.2 | 46.4 | 40.9 | 37.0 | 34.0 | 31.8 | 30.1 |
| 38 | 65.5 | 55.0 | 47.3 | 41.8 | 38.0 | 35.1 | 32.9 | 31.1 |
| 39 | 66.3 | 55.9 | 48.3 | 42.8 | 39.0 | 36.1 | 33.9 | 32.2 |
| 40 | 67.1 | 56.8 | 49.2 | 43.8 | 40.0 | 37.1 | 34.9 | 33.2 |
| 41 | 67.9 | 57.7 | 50.1 | 44.8 | 41.0 | 38.1 | 35.9 | 34.2 |
| 42 | 68.7 | 58.5 | 51.0 | 45.7 | 42.0 | 39.1 | 36.9 | 35.2 |
| 43 | 69.4 | 59.4 | 51.8 | 46.7 | 43.0 | 40.2 | 38.0 | 36.3 |
| 44 | 70.2 | 60.2 | 52.7 | 47.6 | 44.0 | 41.2 | 39.0 | 37.3 |
| 45 | 71.0 | 61.1 | 53.6 | 48.6 | 45.0 | 42.2 | 40.0 | 38.3 |
| 46 | 71.8 | 62.0 | 54.6 | 49.6 | 46.0 | 43.2 | 41.0 | 39.3 |
| 47 | 72.6 | 62.9 | 55.6 | 50.6 | 47.0 | 44.2 | 42.1 | 40.4 |
| 48 | 73.4 | 63.7 | 56.5 | 51.5 | 48.0 | 45.2 | 43.1 | 41.4 |
| 49 | 74.2 | 64.6 | 57.5 | 52.5 | 49.0 | 46.2 | 44.2 | 42.5 |
| 50 | 75.0 | 65.5 | 58.5 | 53.5 | 50.0 | 47.2 | 45.2 | 43.5 |
| 51 | 75.8 | 66.4 | 59.4 | 54.5 | 51.0 | 48.2 | 46.2 | 44.5 |
| 52 | 76.6 | 67.2 | 60.3 | 55.5 | 52.0 | 49.2 | 47.2 | 45.5 |
| 53 | 77.3 | 68.1 | 61.3 | 56.4 | 53.0 | 50.3 | 48.3 | 46.6 |
| 54 | 78.1 | 68.9 | 62.2 | 57.4 | 54.0 | 51.3 | 49.3 | 47.6 |
| 55 | 78.9 | 69.8 | 63.1 | 58.4 | 55.0 | 52.3 | 50.3 | 48.6 |
| 56 | 79.7 | 70.7 | 64.0 | 59.4 | 56.0 | 53.3 | 51.3 | 49.6 |
| 57 | 80.5 | 71.6 | 65.0 | 60.3 | 57.0 | 54.3 | 52.3 | 50.7 |
| 58 | 81.3 | 72.4 | 65.9 | 61.3 | 58.0 | 55.4 | 53.4 | 51.7 |
| 59 | 82.1 | 73.3 | 66.9 | 62.2 | 59.0 | 56.4 | 54.4 | 52.8 |
| 60 | 82.9 | 74.2 | 67.8 | 63.2 | 60.0 | 57.4 | 55.4 | 53.8 |
| 61 | 83.7 | 75.1 | 68.7 | 64.2 | 61.0 | 58.4 | 56.4 | 54.8 |
| 62 | 84.5 | 75.9 | 69.6 | 65.2 | 62.0 | 59.4 | 57.4 | 55.8 |
| 63 | 85.2 | 76.8 | 70.6 | 66.1 | 63.0 | 60.5 | 58.5 | 56.9 |
| 64 | 86.0 | 77.6 | 71.5 | 67.1 | 64.0 | 61.5 | 59.5 | 57.9 |
| 65 | 86.8 | 78.5 | 72.4 | 68.1 | 65.0 | 62.5 | 60.5 | 58.9 |
| 66 | 87.6 | 79.4 | 73.3 | 69.1 | 66.0 | 63.5 | 61.5 | 59.9 |
| 67 | 88.4 | 80.3 | 74.3 | 70.1 | 67.0 | 64.5 | 62.6 | 61.0 |
| 68 | 89.2 | 81.1 | 75.2 | 71.0 | 68.0 | 65.5 | 63.6 | 62.0 |
| 69 | 90.0 | 82.0 | 76.2 | 72.0 | 69.0 | 66.5 | 64.7 | 63.1 |
| 70 | 90.8 | 82.9 | 77.1 | 73.0 | 70.0 | 67.5 | 65.7 | 64.1 |
| 71 | 91.6 | 83.8 | 78.0 | 74.0 | 71.0 | 68.5 | 66.7 | 65.1 |
| 72 | 92.4 | 84.6 | 78.9 | 75.0 | 72.0 | 69.5 | 67.7 | 66.1 |
| 73 | 93.1 | 85.5 | 79.9 | 75.9 | 73.0 | 70.6 | 68.8 | 67.2 |
| 74 | 93.9 | 86.3 | 80.8 | 76.9 | 74.0 | 71.6 | 69.8 | 68.2 |
| 75 | 94.7 | 87.2 | 81.7 | 77.9 | 75.0 | 72.6 | 70.8 | 69.1 |