Nc Noise Criterion
Reference data and engineering information about nc noise criterion for acoustics applications.
noisecriterion
Overview
Engineering reference data for Nc Noise Criterion in acoustics.
Key Formulas
Speed of Sound
Speed of sound in an ideal gas.
Sound Level
Decibel level.
Wavelength
Wavelength = speed / frequency.
Variables
| Symbol | Description | Unit |
|---|---|---|
| Speed of sound | m/s | |
| Sound level | dB | |
| Wavelength | m | |
| Frequency | Hz |
Data Tables
12 rows
NC Rating | 63 Hz(dB) | 125 Hz(dB) | 250 Hz(dB) | 500 Hz(dB) | 1000 Hz(dB) | 2000 Hz(dB) | 4000 Hz(dB) | 8000 Hz(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 |
Source: engineeringtoolbox.com
38 rows
Type of Room / Space | Recommended NC Level | 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 & 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 & 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 & 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 & 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 & recital halls | 15-20 | 25-30 |
| Sport Coliseums | 45-55 | 55-65 |
| Sound broadcasting | 15-20 | 25-30 |
Source: engineeringtoolbox.com
Example Calculation
The following measured sound pressure levels can be used to estimate an NC rating.
| Frequency | Measured SPL |
|---|---|
| 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 |
Plotting these values against the NC curves yields an NC rating of *NC-57.
NCB Curves
Balanced Noise Criteria (NCB) curves are an alternative to the standard NC curves. They are used to specify acceptable background noise levels in occupied spaces, encompassing noise from air-conditioning systems and other ambient sources.