Resources, Tools and Basic Information for Engineering and Design of Technical Applications!
mobile - visible on handheld devices - alternatively go to www.engineeringtoolbox.com!
Engineering ToolBox > NC - Noise Criterion
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 Noise Rating Curves - NR.
The method consists of a set of criteria curves extending from 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 occupant 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.
The noise in different types of rooms should not exceed the Noise Criterion limits listed below:
| Type of Room - Space Type | Recommended NC Level NC Curve | Equivalent Sound Level dBA |
| Apartments | 25-35 | 35-45 |
| Assembly Halls | 25-30 | 35-40 |
| Churches | 30-35 | 40-45 |
| Courtrooms | 30-40 | 40-50 |
| Factories | 40-65 | 50-75 |
| 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 |
The Noise Criterion - NC - of a noise spectrum like
can be estimated to NC = 57 dB as indicated in the diagram below.
