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NC - the Noise Criterion
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Noise Criterion - NC - were established in the U.S. to rate indoor noise like noise from air-
conditioning equipment and similar. In Europe it is common to use the alternative Noise
Rating Curve - NR.
The method is based on a measurement of sound pressure levels and a set of sound
pressure criteria curves ranging frequencies from 63 to 8000 Hz - and a tangent rating
procedure. The criteria curves defines the limits of the octave band spectra that must not
be exceeded to meet the occupants acceptance in the actual spaces.
The NC rating can be determined by plotting the measured sound pressure at each
octave band. The noise spectrum is specified as having a NC rating same as the lowest
NC curve which is not exceeded by the spectrum.
:
Print NC diagram
Noise Criterion - NC - Online Calculator
.
NC - the Noise Criterion
Octave Band Center Frequency (Hz)
Noise Criterion 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
Related Mobile Apps from The Engineering ToolBox
NC Noise Criterion Calculator App
- free apps for offline use on mobile devices.
Recommended Noise Criterion - NC
NC rated noise should not exceed the limits listed below:
Noise Criterion - NC - Recommended Levels
Recommended NC Level Equivalent Sound Level
Type of Room - Space Type dBA
NC Curve
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 - Estimate Rated Noise by using the Noise Criterion
Sound pressure levels are measured for different frequencies as:
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 Criterion can be estimated to
NC = 57 dB
as indicated in the spreadsheet diagram below.
NC - Noise Criterion Example
NC - Noise Criterion - Interactive Spreadsheet
You can save and modify your own copy (in Google Docs or as a Excel spreadsheet) of
the example below.
:
NCB Curves
Balanced Noise Criteria (NCB) curves are used to specify acceptable background noise
levels in occupied spaces and include noise from air-conditioning systems and any other
≡
ambient noise. They are intended to replace the NC curves.
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Related Topics
• Acoustics
Room acoustics and acoustic properties. decibel A, B and C calculations. Noise Rating
(NR) curves. Sound transmission through walls. Calculate sound pressure, sound
intensity and sound attenuation.
Related Documents
Noise - Acceptable dBA Level
Acceptable noise - dBA - level at typical common locations.
Noise Criterion (NC) - Free Online Calculator
Calculate Noise Criterion (NC) from octave band pressure levels.
Noise Criterion vs. Noise Rating and dB(A)
Comparing Noise Criterion (NC, NCB, RNC) to Noise Rating (NR) and dB(A).
Noise Rating (NR) - Free Online Calculator
An online Noise Rating (NR) calculator.
NR - the Noise Rating Curve
The Noise Rating (NR) Curve used to determine acceptable indoor environments for
hearing preservation, speech communication and annoyance.
Octave Band Frequencies
:
The octave and the 1/3 octave band frequencies.
PNC - the Preferred Noise Criterion
A noise measurement system for continuous or ambient noise in indoor environments.
Preferred Noise Criterion (PNC) - Calculator
An online Preferred Noise Criterion (PNC) calculator.
RC - the Room Criteria
The Room Criteria (RC) is used to measure background noise in buildings for frequencies
ranging 16 to 4000 Hz.
Sound - Leq - Equivalent Level
The EPA Equivalent Sound Level - Leq - quantifies the noise environment to a single
value of sound level for any desired duration.
Sound - Ls - Exposure Level
The EPA Sound Exposure Level - Ls - describes the noise from a variable source.
Sound Intensity, Power and Pressure Levels
Introduction to decibel, sound power, intensity and pressure.
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