NC - Noise Criterion

Noise Criterion - NC - level is a standard that describes the relative loudness of a space examining a range of frequencies

Noise Criterion - NC - were established in U.S. for rating indoor noise, noise from air-conditioning equipment etc. In Europe it is common to use the Noise Rating Curve - NR.

The method consists of a set of criteria curves extending 63 to 8000 Hz and a tangency rating procedure. The criteria curves define the limits of octave band spectra that must not be exceeded to meet the occupants acceptance in certain spaces.

The NC rating can be obtained by plotting the octave band levels for a given noise spectrum - the NC curves. The noise spectrum is specified as having a NC rating same as the lowest NC curve which is not exceeded by the spectrum.

nc noise criteria diagram

Noise Criterion Octave Band Center Frequency (Hz)
63 125 250 500 1000 2000 4000 8000
Sound Pressure Levels (dB)
NC-15 47 36 29 22 17 14 12 11
NC-20 51 40 33 26 22 19 17 16
NC-25 54 44 37 31 27 24 22 21
NC-30 57 48 41 35 31 29 28 27
NC-35 60 52 45 40 36 34 33 32
NC-40 64 56 50 45 41 39 38 37
NC-45 67 60 54 49 46 44 43 42
NC-50 71 64 58 54 51 49 48 47
NC-55 74 67 62 58 56 54 53 52
NC-60 77 71 67 63 61 59 58 57
NC-65 80 75 71 68 66 64 63 62
NC-70 83 79 75 72 71 70 69 68

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Recommended Noise Criterion - NC

Noise in different types of rooms should not exceed the Noise Criterion limits as listed below:

Type of Room - Space Type Recommended NC Level
NC Curve
Equivalent Sound Level
dBA
Residences
Apartment Houses 25-35 35-45
Assembly Halls 25-30 35-40
Churches, Synagogues, Mosques 30-35 40-45
Courtrooms 30-40 40-50
Factories 40-65 50-75
Private Homes, rural and suburban 20-30 30-38
Private Homes, urban 25-30 34-42
Hotels/Motels
- Individual rooms or suites 25-35 35-45
- Meeting or banquet rooms 25-35 35-45
- Service and Support Areas 40-45 45-50
- Halls, corridors, lobbies 35-40 50-55
Offices
- Conference rooms 25-30 35-40
- Private 30-35 40-45
- Open-plan areas 35-40 45-50
- Business machines/computers 40-45 50-55
Hospitals and Clinics
- Private rooms 25-30 35-40
- Operating rooms 25-30 35-40
- Wards 30-35 40-45
- Laboratories 35-40 45-50
- Corridors 30-35 40-45
- Public areas 35-40 45-50
Schools
- Lecture and classrooms 25-30 35-40
- Open-plan classrooms 35-40 45-50
Movie motion picture theaters 30-35 40-45
Libraries 35-40 40-50
Legitimate theaters 20-25 30-65
Private Residences 25-35 35-45
Restaurants 40-45 50-55
TV Broadcast studies 15-25 25-35
Recording Studios 15-20 25-30
Concert and recital halls 15-20 25-30
Sport Coliseums 45-55 55-65
Sound broadcasting 15-20 25-30

Example - Estimating NC - Noise Criterion

The Noise Criterion - NC - of a noise spectrum like

  • 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

NC = 57 dB

as indicated in the

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

nc noise criterion exampleNCB Curves

Balanced Noise Criteria (NCB) curves are used to specify acceptable background noise levels in occupied spaces and include air-conditioning an any other ambient noise. They are intended to replace the NC curves.

Related Topics

  • Acoustics - Room acoustics and acoustic properties - decibel A, B and C - Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation

Related Documents

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