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Engineering ToolBox > Comparing Noise Criteria
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.
db(A) (LA) is a weighted method compensating for the human sense of sound pressure at different frequencies.
Choosing the appropriate noise criteria is important when specifying what level of noise is acceptable. Most organizations use a particular index based upon practical experience. It may be appropriate to briefly compare the indices and recommended maximum levels for different types of rooms are listed in the table below:
| Type of Room - Occupancy | Noise Criterion - NC - | Noise Rating - NR | db(A) | |
| Very quiet | Concert and opera halls, recording studios, theaters, etc. | 10 - 20 | 20 | 25 - 30 |
| Private bedrooms, live theaters, television and radio studios, conference and lecture rooms, cathedrals and large churches, libraries, etc. | 20 - 25 | 25 | 25 - 30 | |
| Private living rooms, board rooms, conference and lecture rooms, hotel bedrooms | 30 - 40 | 30 | 30 - 35 | |
| Quiet | Public rooms in hotels, small offices classrooms, courtrooms | 30 - 40 | 35 | 40 - 45 |
| Moderate noisy | Drawing offices, toilets, bathrooms, reception areas, lobbies, corridors, department stores, etc. | 35 - 45 | 40 | 45 - 55 |
| Noisy | Kitchens in hospitals and hotels, laundry rooms, computer rooms, canteens, supermarkets, office landscape, etc. | 40 - 50 | 45 | 45 - 55 |