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# What are NR Levels?

## What are NR Levels?

(OP)
I have been offered a silencer for a very 'noisy' fresh air supply to an emergcey control room.  I have been told that "this silecer will achieve an noise criteia of NR45."

Can anyone tell me what this acutally means and how loud the noise will be with this silencer?

Thanks,

Biggy

### RE: What are NR Levels?

The NR stands for Noise Rating Curve.  Whenever a sound level limit is required for a room or indoors where people are present (usually office environment or similar) the typical criteria used are NR, NCB, NC, RC, PNC etc.

These curves represent sound level limits for the 32 Hertz to 8000 Hertz octave bands.  It means that the sound level in each of the octave bands cannot exceed the specified limit.

For your NC45 the approximate limits are:

32 Hertz Octave Band = 86 dB
63 Hertz Octave Band = 71 dB
125 Hertz Octave Band = 62 dB
250 Hertz Octave Band = 54 dB
500 Hertz Octave Band = 49 dB
1000 Hertz Octave Band = 45 dB
2000 Hertz Octave Band = 43 dB
4000 Hertz Octave Band = 42 dB
8000 Hertz Octave Band = 39 dB

Note that in recent years a the more preferred criterion is NCB which takes low frequency noise into account.  If you had a noise source producing 86 dB at 32 Hertz it would meet the NR45 rating but would sound and feel "rumbly".

C. Hugh (www.Hatch.ca)

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