An introduction to the Noise Rating - NR - Curve developed by the International Organization for Standardization (ISO)
The Noise Rating - NR - curves were first published in ISO Recommendation ISO/R 1996-1971 and is used to determine 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:
|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)|
- NR -
|Octave band mid-frequency (Hz)|
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
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