Noise Criterion - NC - level is a standard describing relative loudness of a space with a range of frequencies
Noise Criterion - NC - were established in the U.S. for rating 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.
Octave Band Analysis (Noise A) Table III-2. Octave Band Analysis (Noise B) Table IV-1. Example Incidence Rates of Nonfatal Occupational Illness; Table IV-2. Inspection Statistics for SIC 2047 - Dog and Cat Food Manufacturing in FY 2011 (Organized by Most Frequently Cited Standard) Table IV-3. Extended Workshifts and Action Level. The sound pressure falls 1/2 times (50%) of the sound pressure of the initial value. It drops with the ratio 1/r of the distance. The sound intensity level decreases with doubling of the distance by (−)6 dB. The intensity falls 1/4 times (25%) of the sound intensity of the initial value. Itdrops with the ratio 1/r 2 of the distance. White noise machines can ease this issue. Many people are looking to find top-rated white noise machines to block out external sounds, but that’s not the only reason to try a sound generator. If that were the case, people would just sleep with earplugs or noise canceling headphones.
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.
| 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 |
Related Mobile Apps from The Engineering ToolBox
- free apps for offline use on mobile devices.
Recommended Noise Criterion - NC
NC rated noise should not exceed the limits 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 - 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
Noise Machine 1 1 76 Inch
The Noise Criterion can be estimated to
NC = 57 dB
as indicated in the spreadsheet diagram below.
Noise Machine 1 1 76 Resz
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.
Noise Machine 1 1 76 Inches
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.
Noise Machine 1 1 760
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
- Acceptable dBA Noise Levels - Acceptable noise - dBA - level at some locations
- Comparing Noise Criteria - Comparing Noise Criteria - Noise Criterion (NC, NCB, RNC), Noise Rating (NR) and dB(A)
- Leq - Equivalent Sound Level - Equivalent Sound Level - Leq - quantifies the noise environment to a single value of sound level for any desired duration
- Ls - Sound Exposure Level - Sound Exposure Level - Ls - describes the noise from a variable source
- Noise Criterion - NC - Online Calculator - An online Noise Criterion - NC - Calculator
- Noise Rating - NR - Online Calculator - An online Noise Rating - NR - Calculator
- NR - Noise Rating Curve - An introduction to the Noise Rating - NR - Curve developed by the International Organization for Standardization (ISO)
- Octave Band Frequencies - Octave and 1/3 octave band frequencies
- PNC - Preferred Noise Criterion - Noise measurement system for continuous or ambient noise in indoor environments
- Preferred Noise Criterion - PNC - Calculator - An online Preferred Noise Criterion - PNC - calculator
- RC - Room Criteria - Room Criteria - RC - measuring background noise in a building over frequencies ranging 16 Hz to 4000 Hz
- Sound Intensity, Power and Pressure Levels - Introduction to decibel, sound power, sound intensity and sound pressure
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