Noise Rating Curves

[izax1]

I need some explanation as to what is meant by NRC (Noise Rating Curves). I have a Spec on Noise criteria, and I have two values: dB(A) and NRC. NRC is lower. How are they related?

 

[Rob45]

NRC more often means "Noise Reduction coefficient."

Is it possible that's what it means here?

Kinda hard to help you though if you don't even know what "dB(A)" means.

 

[VibeAC]

NRC and dBA are two totally different types of acoustical descriptors. Your spec may be referring to NC (Noise Criteria), which is related to dBA.

Andrew Gorton, MSc
Noise & Vibration Consultant

http://www.PapadimosGroup.com

 

[izax1]

Thanks Rob45 and VibeAC. I never said I don't know what dB(A)means. I asked what NRC means and how it is related to dB(A). In my spec. it refers to NRC (Noise Rating Curves)and a link to STANAG 4293. (STANAG=STANdarization AGreemnets)(NATO Standard)

 

[SylvestreW]

Noise Criteria (NC) is common in the US.
Noise Rating (NR) is common in Europe.
For NR curves, see

http://www.engineeringtoolbox.com/nr-noise-rating-d_60.html

Their relation will depend on the spectrum shape.


-
Syl.

 

[hydtools]

I don't find a clear relationship. The NRC or NC number is the single value dB level where the spectrum curve crosses 1kHz. The level dBA is the sum of the sound levels at the octave band center frequencies for an A-weighted spectrum. NRC or NC is a single value number and dBA is a sprectrum sum number.
One exercise I tried was correcting an NC curve to a dBA octave band spectrum and summing octave band levels. The calculated dBA was not in the range of the charted NC-dBA numbers.
One site I found indicated the relationship between NRC and dBA can vary from 0 to +11. Sounds meaningless. Having a clear relationship, that is.

Ted

 

[VibeAC]

Hydtools. I'd go look at some acoustics and noise control books, your summary is off.

Andrew Gorton, MSc
Noise & Vibration Consultant

http://www.PapadimosGroup.com

 

[hydtools]

VibeAC, thanks.
I went back to my calculations and found an error. I recalculated the equivalent dBA of the NC-70 curve to be 77dBA. Seems in line with referenced charts showing NC and equivalent dBA.
Is it fair to conclude then that there is a relationship of NC value and equivalent dBA? Correct the NC octave levels to A-weighted octave levels and sum the resulting A-weighted octave levels to calculate the equivalent dBA.

Ted

 

[SomptingGuy]

This discussion sounds a bit like the search for the Holy Grail of objective measures for subjective noise assessment (big in the late 80's & early 90's).

My favourite was the Composite Rating of Acoustic Preference. Not a good acronym though.

- Steve

 

[SylvestreW]

hyd,
I'd steer clear from trying to document and use a relationship between dBA & NC (or NR). Quite honestly, they are meant for different things, and it's possible that by stating one, you'll miss something.
You are correct that by summing the maximum NC levels you'll end up with a dBA value, but by no means does this imply that, if you are below a certain dBA level, you automatically meet a given NC value.

If the criteria requires NC levels, specify a NC value. If the criteria is a dBA level, specify a dBA level. Realize that both have limitations.

-
Syl.