How Earplugs Are Rated for Noise Reduction — Not What You Think!

How does NRR change decibels of exposure?
When hearing protection is worn, your level of exposure to noise is based on the NRR rating of the protection device being used. Keep in mind, however, that while the NRR is measured in decibels, the hearing protector being used does not reduce the surrounding decibel level by the exact number of decibels associated with that protector’s NRR. For example, if you are at a rock concert where the level of noise exposure is 100 dB and you are wearing earplugs with an NRR 33dB, your level of exposure would not be reduced to 67 dB. Instead, to determine the actual amount of decibel deduction applied (when decibels are measured dBA which is the most common), you take the NRR number (in dB), subtract seven, and then divide by two. Given the previous example, your noise reduction equation would look like the following: (33-7)/2 = 13. This means that if you are at a rock concert with a level of noise exposure at 100 dB and you are wearing a hearing protector with an NRR 33 dB, your new level of noise exposure is 87 dB. If you are wearing a product with an NRR of 27 it would deduct 10 decibels (27-7/2=10).

Pulled from this site... http://www.coopersafety.com/noisereduction.aspx

The CDC and OSHA have more complicated formulas, but was this site had the explanation I could find.

 

I've seen this as well.
But isn't there a difference between NRR and other measurements?
I've noticed that my premolds with -15 dB actually work better than some foamies with - 27 dB NRR.

 

It's more complicated than this. NRR rating is completely inaccurate for those who are wearing plugs correctly. NRR assumes people will be taking protection off and wearing it incorrectly.

http://www.dtic.mil/dtic/tr/fulltext/u2/a501586.pdf
https://pdfs.semanticscholar.org/b76c/999a844d52d02bbc1a3a0f9c4ce0a2dfa1d4.pdf

Real attenuation for plugs ranges from 20dB to about 35dB depending on frequency if worn correctly. If plugs are not inserted correctly they can offer just 0-6dB of protection and most people do not insert foam plugs correctly. With both earmuffs and earplugs in a completely optimal environment the attenuation is at the bone conduction level offering 40+dB protection for most frequencies.

 

Customs actually drop decibels as labeled in like 90 db rooms. I doubt 100 is much different

http://www.audiologyonline.com/articles/making-the-case-for-custom-12959

 

Yeah, I've noticed that I used to unplug my foamies a little to hear the music a bit better and to check the overall volume. With custom you will not do this this easily I think.