Low Speed
Medium Speed
High Speed
Boost
7. Sound Curve
Octave Sound Pressure Level (dB: Overall
A
Scale )
Central Frequency (Cycle per Second)
Hz
dB(A)
63 125 250 500 1000 2000 4000 8000
NR0
NR10
NR20
NR40
NR50
NR60
NR30
60
50
40
30
20
10
The graph below shows Octave Sound Pressure Level for different fan speeds and Frequency
bands. It also shows the NR curves, which specify Maximum Noise Rating Level for various
applications according to the table below.
Noise Rating
C
urve
Maximum Noise
Rating Level
Application
NR 25
Concert halls, broadcasting and recording studios, churches
NR 30
Private dwellings, hospitals, theaters, cinemas, conference rooms
NR 35
Libraries, museums, court rooms, schools, hospitals operating theaters
and wards, flats, hotels, executive offices
NR 40
Halls, corridors, cloakrooms, restaurants, night clubs, offices, shops
NR 45
Department stores, supermarkets, canteens, general offices
NR 50
Typing pools, offices with business machines
NR 60
Light engineering works
NR 70
Foundries, heavy engineering works
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