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Article # 6100

NRR & SNR Defined

What is difference between NRR and SNR?
This is the question most frequently asked when a distributor or end user is looking for technical information on hearing protectors.

NRR: The NRR (noise reduction rating) is a method which attempts to describe a hearing protector based on how much the overall noise level is reduced by the hearing protector. The NRR as a clinical evaluation theoretically provides an estimate of the protection of a given device. The reasons for rating each hearing protector involve OSHA and EPA requirements for product safety and reliability. The rating enables the end user to assess the product 's attenuation abilities for noise in their own given work environment.

SNR: The SNR (single number rating) is the system within the European Union to indicate the amount of protection offered by a correctly fitted hearing protection device.

Tests are performed with test subjects selected at random, with no direct participation from manufacturers. The SNR offers a measurement of the performance using a self-fitting technique.

The numeric results provide an average decibel reduction rating. Additionally, a decibel reduction rating is provided based on groups of related frequencies in Low, Medium and High categories.

In simplified form, an NRR or SNR rating indicates the level that a noise can be reduced by wearing a hearing protection device. Example: If you have a noise level of 110 dBA and you have a NRR or SNR of 30, then the perceived noise level would be reduced to 80 dBA.

Attenuation-USA (ANSI) N.R.R. 33dB
Tested Accordinq to ANSI $3.19-197 4 Standard
Frequency (HZ) 125 250 500 1000 2000 3150 4000 6300 8000
Mean Attenuation
db(A) 33.1 36.3 36.8 38.4 38.7 44.1 45.9 45.4 46
Standard Deviation
db(A) 2.7 1.8 2.1 1.7 2.1 2.3 2.2 2.2 2.4
Attenuation-Europe (EN) : :1-1=35 M=30 L=27 SNR=34dB
EN 352: 1993 Part 21EN 24869-1 :1992
Frequency (I-Iz) 63 125 250 500 1000 2000 4000 8000
Mean Attenuation
dB(A) 27.8 29.1 32.1 34.9 34.4 37.6 47.3 45.4
Standard Deviation
dB(A) 6.1 6.8 6.6 6.5 4.8 4 3.6 5.7
Assumed Protection
dB(A) 21.6 22.4 25.5 28.4 29.5 33.6 43.7 39.7