Bobson
Member
A short while ago, something (I'm not sure what) got me thinking about my Howard Leight earmuffs I use for shooting. IIRC, they have an NRR (Noise Reduction Rating) of 30. They're the bigger, "I look like the guy at the airport" type made by HL. In comparison, the smaller, more compact version produced by Howard Leight (assuming they only make two - those are all I've ever seen at sporting good's stores I frequent) are (again, IIRC) NRR 23.
So I began wondering, what does the Noise Reduction Rating actually mean in terms of noise reduction? So I hopped on the Google machine and learned a couple things.
1. Sound is commonly measured in decibels (dB); most people know that.
2. NRR is not simply a 1:1 ratio of noise reduction.
If you're exposed to a noise measuring 100 dB, and you're wearing NRR 30 earmuffs, you might deduce that your actual exposure is to 70 dB. This is incorrect. NRR is just that - a noise reduction rating: a mathematical expression that, when evaluated for a specific NRR, provides a constant dB reduction. NRR 30 translates to a reduction of roughly 11.5 dB, meaning exposure to a 100 dB sound, with the protection of NRR 30 earmuffs, leaves the wearer exposed to about 88.5 dB. This seems somewhat insignificant. But is it really?
At least one of the sources below indicate that any sound measuring 120 dB (the level typically associated with a "close" clap of thunder) or louder has the ability to cause significant, permanent hearing loss. A gunshot is, on average, about 165 dB. Using hearing protection that rates NRR 30, the average shooter is exposed to 153.5 dB - still a rather dangerous level of noise.
So what about doubling up - using ear plugs under the muffs? That's got to help a lot, right? Not so much. OSHA says that in order to determine the actual reduction level when doubling up, the user should take the NRR of the higher-rated product (generally this will be the earmuff), and get the noise reduction level of that, by using the following formula: (NRR-7)/2. Then, you just add a constant of 5 to the value given by the first part, and you're done.
Example: NRR 30 earmuffs, NRR 18 ear plugs. (30-7)/2 = 11.5 +5 = 16.5. So the result of doubling up with these two specific pieces of hearing protection results in a reduction of 16.5 dB from a given sound. Thus, the shooter who doubles up on hearing protection, and is exposed to the average 165 dB from his firearm, is still exposed to 148.5 decibels. Remember that 120 dB or more can be significantly damaging. That's pretty concerning.
I thought I would share this information, as I've never seen anything about the actual meaning of NRR on this or any other firearm-related board. In discussing suppressors, certain people often cite hearing damage as a primary reason for the full legalization (removal from the NFA) of suppressors. This information may be a very beneficial aid toward that end.
As a brief side note, consider the following:
120 dB can be significantly damaging. The average gunshot is ~165 dB. What does that really mean? It seems like 165 dB may be just a little bit louder than 120 dB. Not so. Using some basic calculus (which you can view below the sources, if interested), we can determine that 165 dB is actually a whopping 45 times louder than 120 dB.
Sources: OSHA, Centers for Disease Control and Prevention, DangerousDecibels.org - a nonprofit funded by many state university medical centers, the CDC, and the National Institute for Occupational Safety and Health (NIOSH).
Math:
Sound intensity (I) is given by I=X(10^0.1L), where L is the loudness measured in decibels (dB), and X is the minimum intensity detectable by the human ear.
For a sound measuring 120 dB, I = X(0.1)ln10(10^0.1(120)); I = X10^120. This means a sound of 120 dB is 10^120 times louder than the minimum intensity detectable by the human ear. That’s a 1 with 120 zeroes behind it.
Likewise, a sound measuring 165 dB is equal to X10^165 (a 1 with 165 zeroes behind it) louder than the minimum intensity sound we can hear. So 165 dB is actually 45 times louder (^165 - ^120) than 120 dB – and not “just a bit louder.” Pretty intense stuff. Anyone know what a 1 with 165 zeroes after it is called? The best I can do is call it approaching infinity.
So I began wondering, what does the Noise Reduction Rating actually mean in terms of noise reduction? So I hopped on the Google machine and learned a couple things.
1. Sound is commonly measured in decibels (dB); most people know that.
2. NRR is not simply a 1:1 ratio of noise reduction.
If you're exposed to a noise measuring 100 dB, and you're wearing NRR 30 earmuffs, you might deduce that your actual exposure is to 70 dB. This is incorrect. NRR is just that - a noise reduction rating: a mathematical expression that, when evaluated for a specific NRR, provides a constant dB reduction. NRR 30 translates to a reduction of roughly 11.5 dB, meaning exposure to a 100 dB sound, with the protection of NRR 30 earmuffs, leaves the wearer exposed to about 88.5 dB. This seems somewhat insignificant. But is it really?
At least one of the sources below indicate that any sound measuring 120 dB (the level typically associated with a "close" clap of thunder) or louder has the ability to cause significant, permanent hearing loss. A gunshot is, on average, about 165 dB. Using hearing protection that rates NRR 30, the average shooter is exposed to 153.5 dB - still a rather dangerous level of noise.
So what about doubling up - using ear plugs under the muffs? That's got to help a lot, right? Not so much. OSHA says that in order to determine the actual reduction level when doubling up, the user should take the NRR of the higher-rated product (generally this will be the earmuff), and get the noise reduction level of that, by using the following formula: (NRR-7)/2. Then, you just add a constant of 5 to the value given by the first part, and you're done.
Example: NRR 30 earmuffs, NRR 18 ear plugs. (30-7)/2 = 11.5 +5 = 16.5. So the result of doubling up with these two specific pieces of hearing protection results in a reduction of 16.5 dB from a given sound. Thus, the shooter who doubles up on hearing protection, and is exposed to the average 165 dB from his firearm, is still exposed to 148.5 decibels. Remember that 120 dB or more can be significantly damaging. That's pretty concerning.
I thought I would share this information, as I've never seen anything about the actual meaning of NRR on this or any other firearm-related board. In discussing suppressors, certain people often cite hearing damage as a primary reason for the full legalization (removal from the NFA) of suppressors. This information may be a very beneficial aid toward that end.
As a brief side note, consider the following:
120 dB can be significantly damaging. The average gunshot is ~165 dB. What does that really mean? It seems like 165 dB may be just a little bit louder than 120 dB. Not so. Using some basic calculus (which you can view below the sources, if interested), we can determine that 165 dB is actually a whopping 45 times louder than 120 dB.
Sources: OSHA, Centers for Disease Control and Prevention, DangerousDecibels.org - a nonprofit funded by many state university medical centers, the CDC, and the National Institute for Occupational Safety and Health (NIOSH).
Math:
Sound intensity (I) is given by I=X(10^0.1L), where L is the loudness measured in decibels (dB), and X is the minimum intensity detectable by the human ear.
For a sound measuring 120 dB, I = X(0.1)ln10(10^0.1(120)); I = X10^120. This means a sound of 120 dB is 10^120 times louder than the minimum intensity detectable by the human ear. That’s a 1 with 120 zeroes behind it.
Likewise, a sound measuring 165 dB is equal to X10^165 (a 1 with 165 zeroes behind it) louder than the minimum intensity sound we can hear. So 165 dB is actually 45 times louder (^165 - ^120) than 120 dB – and not “just a bit louder.” Pretty intense stuff. Anyone know what a 1 with 165 zeroes after it is called? The best I can do is call it approaching infinity.
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