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NR - Noise Rating Curve

An introduction to the Noise Rating - NR - Curve developed by the International Organization for Standardization (ISO)

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The Noise Rating - NR - Curve is developed by the International Organization for Standardization (ISO 1973) to determine the acceptable indoor environment for hearing preservation, speech communication and annoyance. 

The noise rating graphs for different sound pressure levels are plotted at acceptable sound pressure levels at different frequencies. Acceptable sound pressure level vary with the room and the use of it. Different curves are obtained for each type of use. Each curve is obtained by a NR number. 

Note! Noise Rating - NR - is commonly used in Europe. The Noise Criterion - NC - is more common in USA. 

Recommended Noise Rating - NR - Levels

The Noise Rating level should not exceed the values listed below:  

Maximum
Noise Rating
Level
Application
NR 25 Concert halls, broadcasting and recording studios, churches
NR 30 Private dwellings, hospitals, theaters, 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 Curves

Maximum Sound Pressure Level (dB)
Noise Rating
- NR -
Curve
Octave band mid-frequency (Hz)
31.562.51252505001000200040008000
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

NR - Noise Rating Diagram

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Example - Estimating NR - Noise Rating

The sound pressure levels for different NR frequencies are measured to

  • 31.5 Hz : 40 dB
  • 62.5 Hz : 40 dB
  • 125 Hz : 50 dB
  • 250 Hz : 55 dB
  • 500 Hz : 60 dB
  • 1000 Hz : 50 dB
  • 2000 Hz : 55 dB
  • 4000 Hz : 45 dB
  • 8000 Hz : 45 dB

The Noise Rating - NR -  can be estimated as indicated in the spreadsheet diagram below to approximately

NR = 58 dB

Open the NR - Noise Rating example in your browser!

You can save and modify your own copy of the example above if you are signed into your Google Account.

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