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An introduction to Noise Rating - NR - curves - developed by the International Organization for Standardization (ISO)
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The Noise Rating - NR - curves are developed by the International Organization for Standardization (ISO) to determine the acceptable indoor environment for hearing preservation, speech communication and annoyance.
In U.S. it is common to use the Noise Criterion - NC.
The noise rating graphs for different sound pressure levels are plotted at acceptable sound pressure levels at different frequencies. What is acceptable sound pressure level varies with the room and the use of it. There are different curves obtained for each type of use. Each curve is obtained by a NR number.
Note! Noise Rating - NR - is common used in Europe. The Noise Criterion - NC - is more common in USA.
The noise level for different use should not exceed the Noise Ratings listed in the table below:
| Noise rating curve | Application |
| NR 25 | Concert halls, broadcasting and recording studios, churches |
| NR 30 | Private dwellings, hospitals, theatres, cinemas, conference rooms |
| NR 35 | Libraries, museums, court rooms, schools, hospitals operating theaters and wards, flats, hotels, executive offices |
| NR 40 | Halls, corridors, cloakrooms, restaurants, night clubs, offices, shops |
| NR 45 | Department stores, supermarkets, canteens, general offices |
| NR 50 | Typing pools, offices with business machines |
| NR 60 | Light engineering works |
| NR 70 | Foundries, heavy engineering works |
|
Noise Rating
- NR - Curve |
Octave band mid-frequency (Hz) | ||||||||
| 31.5 | 62.5 | 125 | 250 | 500 | 1000 | 2000 | 4000 | 8000 | |
| NR 0 | 55 | 36 | 22 | 12 | 5 | 0 | -4 | -6 | -8 |
| NR 10 | 62 | 43 | 31 | 21 | 15 | 10 | 7 | 4 | 2 |
| NR 20 | 69 | 51 | 39 | 31 | 24 | 20 | 17 | 14 | 13 |
| NR 30 | 76 | 59 | 48 | 40 | 34 | 30 | 27 | 25 | 23 |
| NR 40 | 83 | 67 | 57 | 49 | 44 | 40 | 37 | 35 | 33 |
| NR 50 | 89 | 75 | 66 | 59 | 54 | 50 | 47 | 45 | 44 |
| NR 60 | 96 | 83 | 74 | 68 | 63 | 60 | 57 | 55 | 54 |
| NR 70 | 103 | 91 | 83 | 77 | 73 | 70 | 68 | 66 | 64 |
| NR 80 | 110 | 99 | 92 | 86 | 83 | 80 | 78 | 76 | 74 |
| NR 90 | 117 | 107 | 100 | 96 | 93 | 90 | 88 | 86 | 85 |
| NR 100 | 124 | 115 | 109 | 105 | 102 | 100 | 98 | 96 | 95 |
| NR 110 | 130 | 122 | 118 | 114 | 112 | 110 | 108 | 107 | 105 |
| NR 120 | 137 | 130 | 126 | 124 | 122 | 120 | 118 | 117 | 116 |
| NR 130 | 144 | 138 | 135 | 133 | 131 | 130 | 128 | 127 | 126 |
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