What is Noise Criterion?
Noise Criterion (NC) is a standard used in measuring the relative loudness of a space. It is a set of curves primarily used to describe and rate indoor noise levels.
Buildings, especially indoor spaces, are exposed to different kinds of noise — internal noise from Heating, Ventilation, and Air-Conditioning (HVAC) systems, and external noise such as environmental and weather noise.
It's important that these unwarranted noises are isolated, keeping background noise levels inside the building within an acceptable range. The standard we use to judge whether a space has a good acoustic environment is the Noise Criterion.
Noise Criterion Calculation
Noise Criterion is calculated by measuring the background noise levels in a space and comparing them against a set of curves across 63 Hz to 8000 Hz. The noise criterion of a specific measurement is that of the lowest NC curve which was not exceeded by the actual noise measurement.
Noise Criterion Diagram
The NC curves that a measured noise level is read against are plotted across the octave-band frequency spectrum — the lower the curve a space's noise falls under, the quieter its background noise rating.
Download the NC curve reference diagram (XLSX)
Here are some common building spaces and their recommended Noise Criterion levels:
| Room / Space | Noise Criterion Level |
|---|---|
| Auditoriums | NC 40 |
| Cafeterias | NC 45 |
| Church / Worship Centers | NC 35 |
| Classrooms and Lecture Halls | NC 30 |
| Conference Rooms | NC 35 |
| Hotel Guestrooms | NC 35 |
| Meeting Rooms | NC 35 |
| Music Room, Studio Room, Recording Room | NC 25 |
| Office Spaces | NC 35 |
| Restaurants | NC 45 |
| Retail Spaces | NC 45 |
| Theater / Concert Halls | NC 30 |
TODO (client): the original Noise Criterion curve diagram was supplied as a spreadsheet, not a rendered chart — replace the download link above with a proper chart/figure image when one is available.