NR - Noise Rating Curves

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

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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. 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 common used in Europe. The Noise Criterion - NC - is more common in USA. 

Recommended Noise Rating - NR - Levels

The Noise Rating level for different uses should not exceed the Noise Ratings indicated 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 Curves

Maximum Sound Pressure Level (dB)
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

NR - Noise Rating Diagram

Noise Rating Diagram NR

Example - Estimating NR - Noise Rating

The Noise Rating - NR - of a noise spectrum like

  • 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

can be estimated to NR = 58 dB as indicated in the diagram below.

nr - noise rating diagram example

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Related Topics

  • Acoustics - Room acoustics, acoustic properties - decibel A, B and C - Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity, attenuation and more ..
  • Noise and Attenuation - Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems

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