NRR vs SNR: What's the Difference in Ratings?
If you’re going to shoot, you need hearing protection.
Range safety officers won’t even let you on the firing line without it because gunshots can cause instant hearing damage.
But knowing which ear pro to buy can be complicated. The fact that manufacturers use two different rating systems doesn't make things any easier. If the NRR vs. SNR question has you confused, I’ve got your back.
Here’s everything you need to understand what manufacturers are telling you, and make an informed decision when you’re ready to buy.
NRR vs. SNR
Noise Reduction Rating (NRR) and Single Number Rating (SNR) are two industry standards that manufacturers use to describe how effective various forms of hearing protection are. They’re basically sets of rules that dictate how to test and evaluate hearing protection in a scientific manner.
Basically, NRR and SNR describe how much volume, measured in decibels, the product will reduce before sound waves reach your eardrums.
Neither is necessarily better or worse, but the two standards do approach the issue somewhat differently. I’ll explain what methods go into these ratings, what they mean to the average consumer, and how you can use them to make a buying decision.
What is NRR?
Most manufacturers in the U.S. use Noise Reduction Rating, or NRR, to describe the hearing protection offered by their products.
The governing body for this testing is the American National Standards Institute, or ANSI.
According to EAR Laboratory, the original testing protocol created by ANSI S3.19-1974 allowed manufacturers to use two standard deviations to determine NRR. You don’t need to understand the math that goes into this, but the implications make a difference.
“The use of the 2-SD correction in the NRR is theoretically intended to predict the protection that is achieved by 98% of wearers,” the white paper reads. “This can only be true if the test data are representative of actual use. They aren’t, and thus the 98% protection factor is misleading in the degree of safety that it implies.”
Basically, that means NRR testing assumes that you use the hearing protection exactly as intended. If you don’t, your actual level of hearing protection may be less than the actual NRR.
This changed with the revised standard, ANSI S12.6-2016. The revised protocol considers how effective hearing protection is when used by both trained users and untrained users. Bottom line? NRR is now a more realistic representation of hearing protection than it was prior to 2016.
What is SNR?
Manufacturers who do business internationally or primarily in Europe often prefer to use Single Noise Rating, or SNR, to describe how well their hearing protection works.
The governing body for this testing is the International Organization for Standardization, or ISO. The current standard is ISO 4869-1:208.
According to EAR Laboratory, the biggest advantage of using SNR originally was the ISO’s decision to limit manufacturers to use one standard deviation to determine SNR.
This method assumes greater variation in how consumers actually use their hearing protection. By doing this, SNR gives you a little bit of wiggle room and a more realistic expectation of what your true SNR will be at the shooting range.
Why NRR and SNR Matter
There are a lot of factors that we can use to decide which hearing protection to buy. Things like comfort, size, power source, Bluetooth connectivity, and style all influence our decisions. But, ultimately, we’re buying ear pro to protect our hearing from dangerous volume levels.
Safety ratings expressed as NRR and SNR give us a simple basis of comparison that’s standardized across the industry. Much like NIJ standards for body armor, NRR and SNR figures give consumers confidence that the products we buy can actually back up the manufacturer’s claims.
How to Use NRR and SNR
Both NRR and SNR describe a reduction in volume. The NRR or SNR rating of hearing protection basically tells you how much quieter noises will sound to your ears – kind of like turning down a volume knob by a certain number of settings.
The American Suppressor Association created this firearm-specific graphic which shows that sounds become painful at 120 decibels, and it can cause hearing damage starting at 130 decibels. The average gunshot measures between 130 and 140 decibels on the graphic.
When you use hearing protection, subtract its NRR or SNR from the volume of the gunshot to get a rough idea of what you’ll experience on the range.
For example, hearing protection with an SNR of 28 should reduce the sound of unsuppressed, centerfire gunshots from about 130 to 102 decibels. That puts the volume closer to what you’d hear at a concert or sporting event than at a shooting range.
Shopping for Hearing Protection with NRR vs. SNR
When you’re shopping for ear pro, NRR and SNR safety ratings are both effective tools for comparing hearing protection. As long as you make an apples-to-apples comparison – NRR vs. NRR and SNR vs. SNR – you’ll get an accurate idea of the relative protection offered by two products.
For example, Shellshock hearing protection has earned the following ratings:
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EXO PRO Electronic Earmuff: SNR 28
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EXO PRO Bluetooth Earmuff: SNR 27
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EXO Passive Earmuff: SNR 28
When you need the most hearing protection possible, I recommend using a combination of shooting earplugs and electronic earmuffs like the EXO PRO. When used together, the active hearing protection reduces spikes in volume (like gunshots) to a more hearing-safe volume, and the earplugs reduce the entire audio signal’s volume.
This method is especially helpful at indoor shooting ranges, where you experience not only the sound of gunshots but the combined echo of those sounds bouncing off concrete surfaces.
According to OSHA, “The net result is a change in the intensity of the sound. The sound pressure does not decrease as rapidly as it would in a free field. In other words, it decreases by less than 6 dB each time the distance from the sound source doubles.”
Other Factors that Affect NRR and SNR
To further complicate things, not all sounds affect human ears the same.
As DENIX explains, “The standard for the loudness of sound or noise levels is a quantity known as the ‘decibel (dB).’ The human ear is not uniformly sensitive to all frequencies of sound. Most common sound sources are measured using A-weighted decibels (dBA). The A-weighting corresponds to the ear’s sensitivity and deemphasizes very high and low sound frequencies to only reflect the frequencies that people actually hear. The military typically uses A-weighting to describe sound from generators, aircraft, and general transportation.”
According to Environmental Noise Control, dBa measurements account for the way human ears experience sound, while dBc measurements place emphasis on low-range sounds that we may not hear, but still experience as vibrations.
In addition to volume, the effect of a sound on your ear will vary depending on factors like the sound’s pitch, proximity, and duration. For example, OSHA standard 1926.52 considers a volume of 90 dBa safe for a duration of 8 hours per day; a volume of 115 dBa is only considered safe for 15 minutes per day.
Final Thoughts on NRR vs. SNR Hearing Protection Ratings
You can use both NRR and SNR to decide which hearing protection is right for you, as long as you don’t mix them up. Think of them as inches and centimeters, pounds and kilograms, or MOA and MRAD.
Keep in mind that there are other factors to consider, namely comfort, audio quality, and reaction time. For more information about that, check out our article on Finding the Perfect Fit in Shooting Ear Protection.
Sources
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Department of Defense Environment, Safety & Occupational Health Network and Information Exchange (DENIX)
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