Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

Search is the most efficient way to navigate the Engineering ToolBox!

NC - the Noise Criterion

Sponsored Links

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.

.
NC - the Noise Criterion
Noise CriterionOctave Band Center Frequency (Hz)
631252505001000200040008000
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:

Noise Criterion - NC -  Recommended Levels
Type of Room - Space TypeRecommended 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

The Noise Criterion can be estimated to 

NC = 57 dB

as indicated in the spreadsheet diagram below.

.

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.

Sponsored Links

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.

Sponsored Links

Search Engineering ToolBox

Search is the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics on the AMP pages. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.